Dragonflies are all-terrain insects: Lifeform of the week

Dragonflies are all-terrain insects that spend more of their lives underwater than in the air. They’re also agile, fast and fierce hunters. The majority of their head is taken up by their enormous eyes, and they eat nearly any smaller insect they can see.

An insect ready for action

There are around 7,000 species of dragonflies in the world. They’re found everywhere except Antarctica. Dragonflies live where there are water sources, such as lakes, ponds, swamps and rivers.

These insects are easy to recognize. They have six legs, double transparent wings (sometimes with colored spots) and a long, tubular body. They look a bit like tiny helicopters.

Dragonflies were one of the first insects to inhabit this planet, in the Carboniferous Period (359-299 million years ago). Back then, dragonflies were much bigger. The oldest recorded fossil is around 300 million years old. Some ancient dragonflies had wingspans of up to 2 feet (0.6 meter).

These insects evolved to be smaller, but also faster, more agile and with impressive vision.

Blue and yellow insect perched backward. It has 4 wide open, transparent wings.
There are around 7,000 species of dragonflies in the world. They are fast, agile and voracious hunters. Image via Arie Versluis/ Pexels.

Dragonflies in flight

Unlike other insects, dragonflies are unable to fold their wings over their torso, so they always have them fully extended. Damselflies look very similar, but these creatures fold their wings over their bodies instead of spreading them out to the sides when at rest.

Dragonflies have two pairs of wings with muscles on the thorax (middle section) that work independently, allowing them to change the angle of each. This enables them to fly in any direction, even backward. Hummingbirds, which are the smallest birds in the world, also have this ability.

In addition, dragonflies can hover in one place for more than a minute. They are not only agile, but they’re also fast. Their elongated and thin bodies allow them to fly very quickly. Some species can reach 56 miles per hour (90 kph).

They can also travel great distances. Some species migrate in groups and cover distances of more than 9,000 miles (15,000 km). There are few species in the animal kingdom that can match the dragonfly in its spectacular flight ability.

Long and thin insect perched at the top of a small branch. It has yellowish wings with black areas.
Dragonflies have 2 pairs of wings with muscles on the thorax that work independently, allowing them to fly in any direction. Some species can reach 56 miles per hour (90 kph). Image via Mel Stratton/ Pexels.

A terrifying predator

Dragonflies are absolutely terrifying to smaller insects. They attack their prey from the air with calculated aerial ambushes. And they can measure the speed and trajectory of a target and adjust their flight to intercept it. They are so skilled that they have a success rate of up to 95%. Dragonflies are kind of like flying Rambos.

When hunting, dragonflies capture their prey with their legs and tear off their wings with their sharp jaws so they cannot escape. The anatomy of dragonflies’ legs allows them to catch prey in flight, but not walk with them. But don’t worry, humans are safe from dragonflies. Their jaws are specially designed for chewing, but not for stinging.

In fact, if you hate mosquitoes, then dragonflies will be your best friends, since they help us control these pests. In a single day, dragonflies can consume up to 14% of their body weight. They feed on anything edible that comes within their sight … There’s a reason it’s one of the deadliest predators on the planet.

Close up of the thorax, head, legs and wings of an insect. It looks orange and has enormous red and green eyes.
Dragonflies are absolutely terrifying to smaller insects. They feed on anything edible that comes within their sight and have a success rate of up to 95% when hunting. Image via Oktavianus Mulyadi/ Unsplash.

Look at those big eyes

Dragonflies have some of the largest eyes and most precise vision of all insects. The head is mainly made up of two enormous compound eyes, which meet at the back of the head. Thanks to this, the dragonfly can see 360 degrees of its surroundings without having to turn its head in the slightest.

These compound eyes contain 30,000 small hexagonal panels. Each has its own retina and lens, allowing a dragonfly to see its prey from a distance of up to 40 feet (12 m). Dragonflies also have three simple eyes with simple lenses.

Close up of a yellow insect with big eyes. They look orange at the top and yellow at the bottom. Below them, a bluish area. The eyes have thousands of tiny panels.
Dragonflies have 2 compound eyes and 3 simple eyes. They can see 360 degrees of their surroundings without having to turn their head. Image via Saradasish Pradhan/ Unsplash.

The underwater life of dragonflies

The life cycle of the dragonfly begins when its parents mate, which happens in the air or on land. The female then deposits her eggs in or very close to the water, usually on aquatic plants such as water lilies.

When the eggs hatch, they release the nymphs, which are their underwater form. In this phase, they feed mainly on the larvae of other insects or even tadpoles and fish. As you can see, the dragonfly is already voracious from a very young age.

Once ready for metamorphosis, the nymph emerges from the water clinging to stems, branches and other exposed surfaces, and begins breathing air. Then, the larva’s tough skin opens and the adult dragonfly emerges, ready for an aerial life.

The outer skin the nymph leaves behind, called exuvia, can be found attached to stems and branches for a long time after the dragonfly becomes an adult.

The curious thing is that dragonflies live much longer underwater than out of it. Normally, large nymphs live in water for about five years, and small ones from a few months to around three years. However, they only live a couple of months out of water.

A group of blue insects with transparent wings touching a water surface. The end of their body is underwater.
Before becoming the insects we all know, dragonflies live underwater and look very different from their adult form. These are damselflies laying their eggs in the water. Damselflies look very similar to dragonflies, but these creatures fold their wings over their bodies instead of spreading them out to the sides when at rest. Image via Clément Falize/ Unsplash.

How do dragonflies breathe?

Since these insects live both under and above water, their respiratory system changes. During their phase as nymphs, they breathe through gills at the end of their body, which can be internal or external.

The dragonfly nymph carries the water it takes to the end of its abdomen, where gas exchange takes place. This process allows the nymph to obtain oxygen to breathe. Furthermore, by expelling water, it is capable of propelling itself like a missile, facilitating its ability to move quickly through water.

Exposure to air leads the nymph to initiate respiration. The skin opens at a weak point behind the head and the adult dragonfly crawls out of its larval skin.

Like all insects, dragonflies don’t have lungs, but rather they breathe through tracheas, which are located in the thorax and abdomen.

Dark insect underwater. It has 6 legs, 2 small antennae and a long, thin body that ends in 3 peaks.
As nymphs, they breathe through gills. When adults, they breathe through tracheas. Image via Totodu74/ Wikipedia (public domain).

My dad found a very strange insect swimming underwater in our water lily pond, and then we received the image below at EarthSky Community Photos. All the signs were there for me to write this article …

Small, round, dark insect perched on a long leaf.
View at EarthSky Community Photos. | Our friend Randy Strauss from Walnut Creek Lake, Nebraska, captured this image of a dragonfly nymph on July 24, 2024. He wrote: “I was stumped on what this guy was until a very kind university entomologist identified it for me. It is a dragonfly completing its nymphal stage of life. It had been living in the water and had climbed up onto a vertical surface where it will emerge from its nymphal skin, unfold its wings and appear as a recognizable dragonfly in the teneral stage of its life.” Thank you!

Dragonflies in Japan

The Japanese have great appreciation for dragonflies. In the past, people created designs with this insect, which decorated armor, helmets and weaponry of samurai warriors. Dragonflies were a symbol of agility, power and victory.

Brown helmet that is longer on the sides and back of the head. It has a big butterfly on the top.
Dragonflies were a favorite emblem of the samurai. It was respected for its hunting technique: flying directly toward its prey, never wavering from its path. Image via MET museum (public domain).

Nowadays, excursions are organized to appreciate and study them in their natural environment.

Dragonflies: Head of an insect covered in tiny drops of water. The head looks brown at top, yellow at bottom and green on the sides.
What a wonderful closeup of dew on huge dragonfly eyes. Image via Egor Kamelev/ Pexels.

EarthSky Community Photos

Long and thin insect with a brown body and 4 transparent wings that have some darker spots.
View at EarthSky Community Photos. | Lorraine Boyd from Delmar, New York, photographed this dragonfly and wrote: “An interesting fact is that the dragonflies are among the world’s best hunters with a success rate of 95%.” Aren’t they amazing? Thank you, Lorraine.
A thin and long insect perched on a little branch. It has a round head. Its wings are transparent, white and brown.
View at EarthSky Community Photos. | Steve Price from Kidney Pond, South Jordan, wrote: “Dragonflies are quite territorial. As a result of that, they tend to land on the very same twig, reed or stick every time they take a break from aerial hunting. So I only had to observe a specific dragonfly and wait until it perched nearby. Then I would slowly approach hoping not to scare it away and take the pics. If they do fly off, I just stand there very still up to 5 minutes and sure enough they will land on the very same stick. Patience and a little stealth craft wins the day.” That’s very good advice. Thanks!
Blue, thin insect with transparent wings wide open.
View at EarthSky Community Photos. | Barry Medlin from Georgia wrote: “While walking along the boardwalk at Moody AFB wetlands area, I spotted this Eastern pondhawk (Erythemis simplicicollis) resting on a fence. Lots of different dragonflies in this area, but were too far away for me to get a good shot. This one was the exception!” Very nice pic! Thank you.

More EarthSky Community Photos

Insect with a big, green and black body and a long, thin, black and white tail on a rock.
View at EarthSky Community Photos. | Jane T from Hong Kong, China, wrote: “This green skimmer dragonfly (Orthetrum sabina), with a military-patterned thorax and an artillery-style abdomen or ‘tail’, could almost be a CGI creation from a science fiction movie.” Indeed! Thank you, Jane.
Brown insect with 6 long and thin legs, and a brown and red body.
View at EarthSky Community Photos. | Cecille Kennedy took this photo from Oregon on September 1, 2023, and wrote: “I read that during some events, they are seen in huge numbers in multiple places, sometimes swirling together in giant formations. Last month they were observed making their way along the north Oregon coast in a migration run which takes place when there’s a lot of east winds coming in. No one seems to know where exactly they’re coming from and certainly where they’re going. They remain a mystery on the Oregon and Washington Coast.” Thank you!
A flying insect. It has 4 wings and are positioned like an X letter.
View at EarthSky Community Photos. | Randy Strauss from Walnut Creek Lake, Nebraska, photographed this flying dragonfly and wrote: “To capture a dragonfly in flight I take around a hundred exposures and then sift through them, looking for the one or two that are in focus; these guys are amazingly fast and change direction in a fraction of a second.” They are! Very nice photo. Thank you.

Bottom line: Dragonflies are fierce hunters with a very high success rate. They are agile and fast. And they live underwater much longer than in the air.

Read more: The praying mantis is a predator: Lifeform of the week

Read more: Ants, little but tough: Lifeform of the week

The post Dragonflies are all-terrain insects: Lifeform of the week first appeared on EarthSky.



from EarthSky https://ift.tt/P1MIBsC

Dragonflies are all-terrain insects that spend more of their lives underwater than in the air. They’re also agile, fast and fierce hunters. The majority of their head is taken up by their enormous eyes, and they eat nearly any smaller insect they can see.

An insect ready for action

There are around 7,000 species of dragonflies in the world. They’re found everywhere except Antarctica. Dragonflies live where there are water sources, such as lakes, ponds, swamps and rivers.

These insects are easy to recognize. They have six legs, double transparent wings (sometimes with colored spots) and a long, tubular body. They look a bit like tiny helicopters.

Dragonflies were one of the first insects to inhabit this planet, in the Carboniferous Period (359-299 million years ago). Back then, dragonflies were much bigger. The oldest recorded fossil is around 300 million years old. Some ancient dragonflies had wingspans of up to 2 feet (0.6 meter).

These insects evolved to be smaller, but also faster, more agile and with impressive vision.

Blue and yellow insect perched backward. It has 4 wide open, transparent wings.
There are around 7,000 species of dragonflies in the world. They are fast, agile and voracious hunters. Image via Arie Versluis/ Pexels.

Dragonflies in flight

Unlike other insects, dragonflies are unable to fold their wings over their torso, so they always have them fully extended. Damselflies look very similar, but these creatures fold their wings over their bodies instead of spreading them out to the sides when at rest.

Dragonflies have two pairs of wings with muscles on the thorax (middle section) that work independently, allowing them to change the angle of each. This enables them to fly in any direction, even backward. Hummingbirds, which are the smallest birds in the world, also have this ability.

In addition, dragonflies can hover in one place for more than a minute. They are not only agile, but they’re also fast. Their elongated and thin bodies allow them to fly very quickly. Some species can reach 56 miles per hour (90 kph).

They can also travel great distances. Some species migrate in groups and cover distances of more than 9,000 miles (15,000 km). There are few species in the animal kingdom that can match the dragonfly in its spectacular flight ability.

Long and thin insect perched at the top of a small branch. It has yellowish wings with black areas.
Dragonflies have 2 pairs of wings with muscles on the thorax that work independently, allowing them to fly in any direction. Some species can reach 56 miles per hour (90 kph). Image via Mel Stratton/ Pexels.

A terrifying predator

Dragonflies are absolutely terrifying to smaller insects. They attack their prey from the air with calculated aerial ambushes. And they can measure the speed and trajectory of a target and adjust their flight to intercept it. They are so skilled that they have a success rate of up to 95%. Dragonflies are kind of like flying Rambos.

When hunting, dragonflies capture their prey with their legs and tear off their wings with their sharp jaws so they cannot escape. The anatomy of dragonflies’ legs allows them to catch prey in flight, but not walk with them. But don’t worry, humans are safe from dragonflies. Their jaws are specially designed for chewing, but not for stinging.

In fact, if you hate mosquitoes, then dragonflies will be your best friends, since they help us control these pests. In a single day, dragonflies can consume up to 14% of their body weight. They feed on anything edible that comes within their sight … There’s a reason it’s one of the deadliest predators on the planet.

Close up of the thorax, head, legs and wings of an insect. It looks orange and has enormous red and green eyes.
Dragonflies are absolutely terrifying to smaller insects. They feed on anything edible that comes within their sight and have a success rate of up to 95% when hunting. Image via Oktavianus Mulyadi/ Unsplash.

Look at those big eyes

Dragonflies have some of the largest eyes and most precise vision of all insects. The head is mainly made up of two enormous compound eyes, which meet at the back of the head. Thanks to this, the dragonfly can see 360 degrees of its surroundings without having to turn its head in the slightest.

These compound eyes contain 30,000 small hexagonal panels. Each has its own retina and lens, allowing a dragonfly to see its prey from a distance of up to 40 feet (12 m). Dragonflies also have three simple eyes with simple lenses.

Close up of a yellow insect with big eyes. They look orange at the top and yellow at the bottom. Below them, a bluish area. The eyes have thousands of tiny panels.
Dragonflies have 2 compound eyes and 3 simple eyes. They can see 360 degrees of their surroundings without having to turn their head. Image via Saradasish Pradhan/ Unsplash.

The underwater life of dragonflies

The life cycle of the dragonfly begins when its parents mate, which happens in the air or on land. The female then deposits her eggs in or very close to the water, usually on aquatic plants such as water lilies.

When the eggs hatch, they release the nymphs, which are their underwater form. In this phase, they feed mainly on the larvae of other insects or even tadpoles and fish. As you can see, the dragonfly is already voracious from a very young age.

Once ready for metamorphosis, the nymph emerges from the water clinging to stems, branches and other exposed surfaces, and begins breathing air. Then, the larva’s tough skin opens and the adult dragonfly emerges, ready for an aerial life.

The outer skin the nymph leaves behind, called exuvia, can be found attached to stems and branches for a long time after the dragonfly becomes an adult.

The curious thing is that dragonflies live much longer underwater than out of it. Normally, large nymphs live in water for about five years, and small ones from a few months to around three years. However, they only live a couple of months out of water.

A group of blue insects with transparent wings touching a water surface. The end of their body is underwater.
Before becoming the insects we all know, dragonflies live underwater and look very different from their adult form. These are damselflies laying their eggs in the water. Damselflies look very similar to dragonflies, but these creatures fold their wings over their bodies instead of spreading them out to the sides when at rest. Image via Clément Falize/ Unsplash.

How do dragonflies breathe?

Since these insects live both under and above water, their respiratory system changes. During their phase as nymphs, they breathe through gills at the end of their body, which can be internal or external.

The dragonfly nymph carries the water it takes to the end of its abdomen, where gas exchange takes place. This process allows the nymph to obtain oxygen to breathe. Furthermore, by expelling water, it is capable of propelling itself like a missile, facilitating its ability to move quickly through water.

Exposure to air leads the nymph to initiate respiration. The skin opens at a weak point behind the head and the adult dragonfly crawls out of its larval skin.

Like all insects, dragonflies don’t have lungs, but rather they breathe through tracheas, which are located in the thorax and abdomen.

Dark insect underwater. It has 6 legs, 2 small antennae and a long, thin body that ends in 3 peaks.
As nymphs, they breathe through gills. When adults, they breathe through tracheas. Image via Totodu74/ Wikipedia (public domain).

My dad found a very strange insect swimming underwater in our water lily pond, and then we received the image below at EarthSky Community Photos. All the signs were there for me to write this article …

Small, round, dark insect perched on a long leaf.
View at EarthSky Community Photos. | Our friend Randy Strauss from Walnut Creek Lake, Nebraska, captured this image of a dragonfly nymph on July 24, 2024. He wrote: “I was stumped on what this guy was until a very kind university entomologist identified it for me. It is a dragonfly completing its nymphal stage of life. It had been living in the water and had climbed up onto a vertical surface where it will emerge from its nymphal skin, unfold its wings and appear as a recognizable dragonfly in the teneral stage of its life.” Thank you!

Dragonflies in Japan

The Japanese have great appreciation for dragonflies. In the past, people created designs with this insect, which decorated armor, helmets and weaponry of samurai warriors. Dragonflies were a symbol of agility, power and victory.

Brown helmet that is longer on the sides and back of the head. It has a big butterfly on the top.
Dragonflies were a favorite emblem of the samurai. It was respected for its hunting technique: flying directly toward its prey, never wavering from its path. Image via MET museum (public domain).

Nowadays, excursions are organized to appreciate and study them in their natural environment.

Dragonflies: Head of an insect covered in tiny drops of water. The head looks brown at top, yellow at bottom and green on the sides.
What a wonderful closeup of dew on huge dragonfly eyes. Image via Egor Kamelev/ Pexels.

EarthSky Community Photos

Long and thin insect with a brown body and 4 transparent wings that have some darker spots.
View at EarthSky Community Photos. | Lorraine Boyd from Delmar, New York, photographed this dragonfly and wrote: “An interesting fact is that the dragonflies are among the world’s best hunters with a success rate of 95%.” Aren’t they amazing? Thank you, Lorraine.
A thin and long insect perched on a little branch. It has a round head. Its wings are transparent, white and brown.
View at EarthSky Community Photos. | Steve Price from Kidney Pond, South Jordan, wrote: “Dragonflies are quite territorial. As a result of that, they tend to land on the very same twig, reed or stick every time they take a break from aerial hunting. So I only had to observe a specific dragonfly and wait until it perched nearby. Then I would slowly approach hoping not to scare it away and take the pics. If they do fly off, I just stand there very still up to 5 minutes and sure enough they will land on the very same stick. Patience and a little stealth craft wins the day.” That’s very good advice. Thanks!
Blue, thin insect with transparent wings wide open.
View at EarthSky Community Photos. | Barry Medlin from Georgia wrote: “While walking along the boardwalk at Moody AFB wetlands area, I spotted this Eastern pondhawk (Erythemis simplicicollis) resting on a fence. Lots of different dragonflies in this area, but were too far away for me to get a good shot. This one was the exception!” Very nice pic! Thank you.

More EarthSky Community Photos

Insect with a big, green and black body and a long, thin, black and white tail on a rock.
View at EarthSky Community Photos. | Jane T from Hong Kong, China, wrote: “This green skimmer dragonfly (Orthetrum sabina), with a military-patterned thorax and an artillery-style abdomen or ‘tail’, could almost be a CGI creation from a science fiction movie.” Indeed! Thank you, Jane.
Brown insect with 6 long and thin legs, and a brown and red body.
View at EarthSky Community Photos. | Cecille Kennedy took this photo from Oregon on September 1, 2023, and wrote: “I read that during some events, they are seen in huge numbers in multiple places, sometimes swirling together in giant formations. Last month they were observed making their way along the north Oregon coast in a migration run which takes place when there’s a lot of east winds coming in. No one seems to know where exactly they’re coming from and certainly where they’re going. They remain a mystery on the Oregon and Washington Coast.” Thank you!
A flying insect. It has 4 wings and are positioned like an X letter.
View at EarthSky Community Photos. | Randy Strauss from Walnut Creek Lake, Nebraska, photographed this flying dragonfly and wrote: “To capture a dragonfly in flight I take around a hundred exposures and then sift through them, looking for the one or two that are in focus; these guys are amazingly fast and change direction in a fraction of a second.” They are! Very nice photo. Thank you.

Bottom line: Dragonflies are fierce hunters with a very high success rate. They are agile and fast. And they live underwater much longer than in the air.

Read more: The praying mantis is a predator: Lifeform of the week

Read more: Ants, little but tough: Lifeform of the week

The post Dragonflies are all-terrain insects: Lifeform of the week first appeared on EarthSky.



from EarthSky https://ift.tt/P1MIBsC
Aucun commentaire:
Libellés :

LIVE on Monday: Moon crazy, with Robert Reeves

The Earth and its moon are locked together in a codependent embrace. How does the moon impact our lives? Robert Reeves is a prolific astrophotographer, astronomy writer, and dedicated selenophile (person who loves the moon). His newest book, Photographic Atlas of the Moon, published on September 1 at Firefly Books. We’ll be speaking with Robert at 12:15 CDT (17:15 UTC) on Monday, September 9. Join us, moon lovers!

Robert Reeves has been exploring the cosmos since 1958, and took his first lunar photograph in 1959. Since then, he has published over 250 magazine articles, 250 newspaper columns, and several books about astronomy and astrophotography. While also an accomplished deep-sky astrophotographer, Robert’s current focus is the moon. He’s passionate about re-popularizing the moon within the amateur astronomy community by explaining its origin and the evolution of its face, and introducing its geology to stargazers everywhere.

Moon expert Robert Reeves, a white man with glasses, standing to the left of a large, complex home telescope.
Veteran astrophotographer and certified moon lover Robert Reeves.

On top of his recently published Photographic Atlas of the Moon, he released another lunar guide, Exploring the Moon with Robert Reeves, in August 2023. And for many years, Robert published a different lunar photograph in a daily posting called 365 Days of the Moon. Today, he continues this tradition with his daily Postcard from the Moon, highlighting different lunar features each day. Tune in on Monday, September 9, when Robert will be talking through some of his favorite spots on the moon, and giving more tips about to how to appreciate Earth’s own natural satellite.

Bottom line: Join us from 12:15 CDT (17:15 UTC) on Monday, September 9, 2024, as lunar astrophotographer Robert Reeves discusses ways to appreciate our moon.

The post LIVE on Monday: Moon crazy, with Robert Reeves first appeared on EarthSky.



from EarthSky https://ift.tt/wTeN8L5

The Earth and its moon are locked together in a codependent embrace. How does the moon impact our lives? Robert Reeves is a prolific astrophotographer, astronomy writer, and dedicated selenophile (person who loves the moon). His newest book, Photographic Atlas of the Moon, published on September 1 at Firefly Books. We’ll be speaking with Robert at 12:15 CDT (17:15 UTC) on Monday, September 9. Join us, moon lovers!

Robert Reeves has been exploring the cosmos since 1958, and took his first lunar photograph in 1959. Since then, he has published over 250 magazine articles, 250 newspaper columns, and several books about astronomy and astrophotography. While also an accomplished deep-sky astrophotographer, Robert’s current focus is the moon. He’s passionate about re-popularizing the moon within the amateur astronomy community by explaining its origin and the evolution of its face, and introducing its geology to stargazers everywhere.

Moon expert Robert Reeves, a white man with glasses, standing to the left of a large, complex home telescope.
Veteran astrophotographer and certified moon lover Robert Reeves.

On top of his recently published Photographic Atlas of the Moon, he released another lunar guide, Exploring the Moon with Robert Reeves, in August 2023. And for many years, Robert published a different lunar photograph in a daily posting called 365 Days of the Moon. Today, he continues this tradition with his daily Postcard from the Moon, highlighting different lunar features each day. Tune in on Monday, September 9, when Robert will be talking through some of his favorite spots on the moon, and giving more tips about to how to appreciate Earth’s own natural satellite.

Bottom line: Join us from 12:15 CDT (17:15 UTC) on Monday, September 9, 2024, as lunar astrophotographer Robert Reeves discusses ways to appreciate our moon.

The post LIVE on Monday: Moon crazy, with Robert Reeves first appeared on EarthSky.



from EarthSky https://ift.tt/wTeN8L5
Aucun commentaire:
Libellés :

What does opposition mean for an outer planet?

Diagram: the sun in the center, and Earth between Saturn and the sun. Planets' orbits shown.
Artist’s concept of Saturn in opposition to the sun. Not to scale. Image via NASA.

You might have heard that opposition is the best time of year to observe a planet. But what is opposition? And which planets have oppositions? In astronomy, opposition means a planet is opposite the sun as viewed from Earth. So, for example, the planets with orbits inside Earth’s orbit (Mercury and Venus) can’t be in opposition. But the planets orbiting outside Earth’s orbit (Mars, Jupiter, Saturn, Uranus, Neptune) all can.

Once each year, we pass between them and the sun in our smaller, faster orbit. If the sun is setting in the west, and Jupiter is rising in the east, then Jupiter is at opposition. Earth is passing between the sun and Jupiter, which will, therefore, take all night to cross our sky. At opposition, a planet is easiest to observe because it’s generally closest to Earth and visible throughout the night.

Diagram showing Earth between an outer planet and the sun. Orbits shown.
Opposition happens when Earth flies between an outer planet, like Saturn, and the sun. Illustration via Heavens-Above. Used with permission.

Look at the diagram above. The sun is in the center of the diagram. Earth is a little way out, and Saturn farther still. As seen from above our solar system, the planets are moving counterclockwise around the sun. Now, run this diagram forward in your mind. Because it’s in an inner orbit, Earth travels faster than Saturn. And Jupiter (not shown) travels faster than Saturn. Of course, the planets will be in various configurations as seen from above the solar system. But, in nearly every earthly year, Earth will pass between the outer planets and the sun. This is opposition.

An opposition as seen from Earth

At opposition, Earth is in the middle of a line between an outer planet and the sun, and we see the sun at one end of our sky and the opposition planet in the opposite direction. It’s as if you’re standing directly between two friends as you chat in the supermarket, and you need to turn your head halfway around to see one and then the other. At opposition, the sun is on the opposite side of the sky from the outer planet; when the sun sets in the west, the planet is rising in the east. As the planet drops below the horizon, the sun pops above it again: opposite.

To be technical, opposition for an outer planet happens when the sun and that planet are exactly 180 degrees apart in the sky. The word comes to English from a Latin root, meaning to set against.

Consider that Venus and Mercury can never be at opposition as seen from Earth. Their orbits are closer to the sun than Earth’s, so they can never appear opposite the sun in our sky. You will never see Venus in the east, for example, when the sun is setting in the west. These inner planets always stay near the sun from our point of view, no more than 47 degrees from the sun for Venus, or 28 degrees for Mercury.

Oppositions can only happen for objects that are farther from the sun than Earth is. We see oppositions for Jupiter, Saturn, Uranus, and Neptune about every year. They happen as Earth, in its much-faster orbit, passes between these outer worlds and the sun. We see oppositions of the planet Mars, too, but Martian oppositions happen about every 27 months, because Earth and Mars are so relatively close together in orbit around the sun. Their orbits, and speeds in orbit, are more similar.

Dates of upcoming oppositions

Since everything in space is always moving, oppositions of planets farther than us from the sun happen again and again. As far as the bright planets go, the next opposition is never too far away:

Note: Dates are based on UTC time.

Mars was at opposition on December 8, 2022, and will be again on January 16, 2025.

Jupiter was at opposition on November 2-3, 2023, and will be again on December 7, 2024.

Saturn was at opposition on August 26-27, 2023, and will be again on September 8, 2024.

Uranus will be at opposition on November 13, 2023, and next on November 17, 2024.

Neptune will be at opposition on September 19, 2023, and next on September 21, 2024.

Note that Jupiter’s oppositions come about a month later each year. Saturn’s come about two weeks later each year. Uranus and Neptune opposition dates come only a few days later, year after year.

Mars as orangish ball with dark and light markings and white at south pole.
View at EarthSky Community Photos. | Patrick Prokop in Savannah, Georgia, took this image of Mars on November 29, 2022. Patrick wrote: “The planet Mars 9 days before opposition. It was just shy of 51 million miles away at the time. I took this image when Mars was 60 degrees in elevation in my backyard. Since my location is only 3 meters (9 feet) above sea level, I was looking through a lot of atmosphere, which distorts the view.” Thank you, Patrick!
A dark twilight sky, with two trees in foreground, and many stars and two bright planets.
View at EarthSky Community Photos. | Joel Weatherly in Edmonton, Alberta, Canada, captured this wide-angle photo of the sky with Jupiter and Saturn on August 12, 2021, and wrote: “Jupiter and Saturn have been lovely this August as they both reach opposition during the month. This image was taken during a brief pause in the Perseid meteor shower when bright Jupiter caught my eye.” Thank you, Joel!

Why are planets at opposition so interesting to sky-watchers?

As mentioned, because they’re opposite the sun, planets at opposition rise when the sun sets and can be found somewhere in the sky throughout the night.

Secondly, planets at opposition tend to be near their closest point to Earth in orbit. Due to the non-circular shape of planetary orbits, the exact closest point might be different by a day or two, as will be the case for Jupiter in 2024. Jupiter’s opposition is on December 7, 2024, and its exact closest point will be on December 6. Still, for many weeks around opposition – between the time we pass between an outer planet and the sun – the outer planet is generally closest to Earth. At such a time, the planet is brightest, and more detail can be seen through telescopes.

And here’s another interesting aspect of opposition. Since the sun and outer planet are directly opposite each other in Earth’s sky, we see that far-off planet’s fully lit daytime side. Fully lit planets appear brighter to us than ones not completely lit. If you’re saying to yourself that this sounds a lot like the moon, you’re right! After all, what’s a full moon if not the moon at opposition? During the moon’s full phase, it’s directly opposite the sun in the sky, fully illuminated, and at its brightest for that orbit. As it moves through the rest of its orbit, the sun-Earth-moon line bends and gives us what we see from Earth as the moon’s phases.

Oppositions from other planets

Like so much in life, opposition is all about point of view. We’ve been talking about the view from Earth. What if we flip it around?

When an outer planet – let’s say Jupiter – is at opposition for us, Earth is at inferior conjunction as seen from that planet. In other words, at the moment of opposition for us on Earth, observers on Jupiter would see Earth passing between their world and the sun. The Earth and the sun would be in the same side of Jupiter’s sky, Earth hidden in the sun’s glare except to skilled observers using special equipment.

Consider also that the line from the sun to Jupiter passes through the Earth, which means Earth passes directly between the sun and Jupiter. Maybe one day, a visitor to Jupiter will see Earth transit the sun as seen from Jupiter. That is, they’ll see Earth’s darkened nighttime side, and all of humanity, cross the face of the sun from half a billion miles away.

A slightly fuzzy telescopic view of colorful, striped Saturn and its rings.
Patrick Prokop in Savannah, Georgia, caught this magnificent image of golden Saturn on July 3, 2019, a few days before opposition. Thank you, Patrick!

Bottom line: The ideal time to observe a planet is around opposition. During opposition, Earth passes between an outer planet and the sun, placing the planet opposite the sun in our sky. A planet at opposition is closest to Earth in its orbit and bright. It rises when the sun sets, and so is visible all night.

Read more: Saturn at opposition September 8, 2024

Read more: Jupiter at opposition December 7, 2024

The post What does opposition mean for an outer planet? first appeared on EarthSky.



from EarthSky https://ift.tt/DTneFHc
Diagram: the sun in the center, and Earth between Saturn and the sun. Planets' orbits shown.
Artist’s concept of Saturn in opposition to the sun. Not to scale. Image via NASA.

You might have heard that opposition is the best time of year to observe a planet. But what is opposition? And which planets have oppositions? In astronomy, opposition means a planet is opposite the sun as viewed from Earth. So, for example, the planets with orbits inside Earth’s orbit (Mercury and Venus) can’t be in opposition. But the planets orbiting outside Earth’s orbit (Mars, Jupiter, Saturn, Uranus, Neptune) all can.

Once each year, we pass between them and the sun in our smaller, faster orbit. If the sun is setting in the west, and Jupiter is rising in the east, then Jupiter is at opposition. Earth is passing between the sun and Jupiter, which will, therefore, take all night to cross our sky. At opposition, a planet is easiest to observe because it’s generally closest to Earth and visible throughout the night.

Diagram showing Earth between an outer planet and the sun. Orbits shown.
Opposition happens when Earth flies between an outer planet, like Saturn, and the sun. Illustration via Heavens-Above. Used with permission.

Look at the diagram above. The sun is in the center of the diagram. Earth is a little way out, and Saturn farther still. As seen from above our solar system, the planets are moving counterclockwise around the sun. Now, run this diagram forward in your mind. Because it’s in an inner orbit, Earth travels faster than Saturn. And Jupiter (not shown) travels faster than Saturn. Of course, the planets will be in various configurations as seen from above the solar system. But, in nearly every earthly year, Earth will pass between the outer planets and the sun. This is opposition.

An opposition as seen from Earth

At opposition, Earth is in the middle of a line between an outer planet and the sun, and we see the sun at one end of our sky and the opposition planet in the opposite direction. It’s as if you’re standing directly between two friends as you chat in the supermarket, and you need to turn your head halfway around to see one and then the other. At opposition, the sun is on the opposite side of the sky from the outer planet; when the sun sets in the west, the planet is rising in the east. As the planet drops below the horizon, the sun pops above it again: opposite.

To be technical, opposition for an outer planet happens when the sun and that planet are exactly 180 degrees apart in the sky. The word comes to English from a Latin root, meaning to set against.

Consider that Venus and Mercury can never be at opposition as seen from Earth. Their orbits are closer to the sun than Earth’s, so they can never appear opposite the sun in our sky. You will never see Venus in the east, for example, when the sun is setting in the west. These inner planets always stay near the sun from our point of view, no more than 47 degrees from the sun for Venus, or 28 degrees for Mercury.

Oppositions can only happen for objects that are farther from the sun than Earth is. We see oppositions for Jupiter, Saturn, Uranus, and Neptune about every year. They happen as Earth, in its much-faster orbit, passes between these outer worlds and the sun. We see oppositions of the planet Mars, too, but Martian oppositions happen about every 27 months, because Earth and Mars are so relatively close together in orbit around the sun. Their orbits, and speeds in orbit, are more similar.

Dates of upcoming oppositions

Since everything in space is always moving, oppositions of planets farther than us from the sun happen again and again. As far as the bright planets go, the next opposition is never too far away:

Note: Dates are based on UTC time.

Mars was at opposition on December 8, 2022, and will be again on January 16, 2025.

Jupiter was at opposition on November 2-3, 2023, and will be again on December 7, 2024.

Saturn was at opposition on August 26-27, 2023, and will be again on September 8, 2024.

Uranus will be at opposition on November 13, 2023, and next on November 17, 2024.

Neptune will be at opposition on September 19, 2023, and next on September 21, 2024.

Note that Jupiter’s oppositions come about a month later each year. Saturn’s come about two weeks later each year. Uranus and Neptune opposition dates come only a few days later, year after year.

Mars as orangish ball with dark and light markings and white at south pole.
View at EarthSky Community Photos. | Patrick Prokop in Savannah, Georgia, took this image of Mars on November 29, 2022. Patrick wrote: “The planet Mars 9 days before opposition. It was just shy of 51 million miles away at the time. I took this image when Mars was 60 degrees in elevation in my backyard. Since my location is only 3 meters (9 feet) above sea level, I was looking through a lot of atmosphere, which distorts the view.” Thank you, Patrick!
A dark twilight sky, with two trees in foreground, and many stars and two bright planets.
View at EarthSky Community Photos. | Joel Weatherly in Edmonton, Alberta, Canada, captured this wide-angle photo of the sky with Jupiter and Saturn on August 12, 2021, and wrote: “Jupiter and Saturn have been lovely this August as they both reach opposition during the month. This image was taken during a brief pause in the Perseid meteor shower when bright Jupiter caught my eye.” Thank you, Joel!

Why are planets at opposition so interesting to sky-watchers?

As mentioned, because they’re opposite the sun, planets at opposition rise when the sun sets and can be found somewhere in the sky throughout the night.

Secondly, planets at opposition tend to be near their closest point to Earth in orbit. Due to the non-circular shape of planetary orbits, the exact closest point might be different by a day or two, as will be the case for Jupiter in 2024. Jupiter’s opposition is on December 7, 2024, and its exact closest point will be on December 6. Still, for many weeks around opposition – between the time we pass between an outer planet and the sun – the outer planet is generally closest to Earth. At such a time, the planet is brightest, and more detail can be seen through telescopes.

And here’s another interesting aspect of opposition. Since the sun and outer planet are directly opposite each other in Earth’s sky, we see that far-off planet’s fully lit daytime side. Fully lit planets appear brighter to us than ones not completely lit. If you’re saying to yourself that this sounds a lot like the moon, you’re right! After all, what’s a full moon if not the moon at opposition? During the moon’s full phase, it’s directly opposite the sun in the sky, fully illuminated, and at its brightest for that orbit. As it moves through the rest of its orbit, the sun-Earth-moon line bends and gives us what we see from Earth as the moon’s phases.

Oppositions from other planets

Like so much in life, opposition is all about point of view. We’ve been talking about the view from Earth. What if we flip it around?

When an outer planet – let’s say Jupiter – is at opposition for us, Earth is at inferior conjunction as seen from that planet. In other words, at the moment of opposition for us on Earth, observers on Jupiter would see Earth passing between their world and the sun. The Earth and the sun would be in the same side of Jupiter’s sky, Earth hidden in the sun’s glare except to skilled observers using special equipment.

Consider also that the line from the sun to Jupiter passes through the Earth, which means Earth passes directly between the sun and Jupiter. Maybe one day, a visitor to Jupiter will see Earth transit the sun as seen from Jupiter. That is, they’ll see Earth’s darkened nighttime side, and all of humanity, cross the face of the sun from half a billion miles away.

A slightly fuzzy telescopic view of colorful, striped Saturn and its rings.
Patrick Prokop in Savannah, Georgia, caught this magnificent image of golden Saturn on July 3, 2019, a few days before opposition. Thank you, Patrick!

Bottom line: The ideal time to observe a planet is around opposition. During opposition, Earth passes between an outer planet and the sun, placing the planet opposite the sun in our sky. A planet at opposition is closest to Earth in its orbit and bright. It rises when the sun sets, and so is visible all night.

Read more: Saturn at opposition September 8, 2024

Read more: Jupiter at opposition December 7, 2024

The post What does opposition mean for an outer planet? first appeared on EarthSky.



from EarthSky https://ift.tt/DTneFHc
Aucun commentaire:
Libellés :

Orion’s Belt points to Sirius on September mornings

Sky chart showing Orion and Sirius with arrow from Orion's Belt to the star.
Look for the easy-to-see constellation Orion the Hunter in the predawn sky in September. Then draw an imaginary line between the 3 stars in Orion’s Belt. That line will point to Sirius, the sky’s brightest star.

Orion’s Belt points to Sirius

It’s one of the neatest tricks in all the heavens: Orion’s Belt points to Sirius, the sky’s brightest star. So on September mornings, you’ll find both Orion the Hunter and the very bright star Sirius in the eastern part of the sky before dawn. Before you know it, they’ll be shifting into the evening sky. Identify them now, and enjoy them for months to come.

Also, sometimes there are bright planets that might outshine even Sirius, in the same region. In fact, in September 2024, Jupiter is also in the morning sky and definitely outshines our brightest star. Mars is there too, but it’s not as bright as Jupiter or Sirius.

What’s more, sometimes there are bright planets in the evening sky during the northern winter, when Orion and Sirius shine brightly. And those planets, too, might be brighter than the sky’s brightest star. In those cases, how can you be sure the object you’re looking at is Sirius? The constellation Orion is your ticket. No matter where you are, no matter what time of the year it is, Orion’s Belt always points to Sirius.

Orion returned to the morning sky in late July

Orion returned to the sky before dawn in late July and early August. In September, you can easily find this large constellation before sunup. Just look in the eastern part of the sky. You’ll easily notice Orion’s Belt, which consists of a short, straight row of three medium-bright stars.

To find Sirius, draw a line through Orion’s Belt and extend that line toward the horizon. There, you’ll spot Sirius, the sky’s brightest star.

Sirius is in the constellation Canis Major the Greater Dog. It’s often called the Dog Star.

Wide array of bright but slightly fuzzy stars, mostly blue-white but one reddish, over dark landscape.
View at EarthSky Community Photos. | Sergei Timofeevski shared this image from November 13, 2023. Sergei wrote: “The constellation Orion the Hunter and the star Sirius rising just above the eastern horizon in the Anza-Borrego Desert State Park, California.” Thank you, Sergei! Note bright Sirius is on the bottom, and Orion’s Belt pointing to it.

Bottom line: In September 2024, you’ll find the constellation Orion, whose three Belt stars make a short, straight row, in the southeast before dawn. Orion’s Belt points to Sirius, the brightest star of the nighttime sky. Only (some) planets shine brighter.

Help support EarthSky! Check out the EarthSky store for fun astronomy gifts and tools for all ages!

The post Orion’s Belt points to Sirius on September mornings first appeared on EarthSky.



from EarthSky https://ift.tt/RPnfNMi
Sky chart showing Orion and Sirius with arrow from Orion's Belt to the star.
Look for the easy-to-see constellation Orion the Hunter in the predawn sky in September. Then draw an imaginary line between the 3 stars in Orion’s Belt. That line will point to Sirius, the sky’s brightest star.

Orion’s Belt points to Sirius

It’s one of the neatest tricks in all the heavens: Orion’s Belt points to Sirius, the sky’s brightest star. So on September mornings, you’ll find both Orion the Hunter and the very bright star Sirius in the eastern part of the sky before dawn. Before you know it, they’ll be shifting into the evening sky. Identify them now, and enjoy them for months to come.

Also, sometimes there are bright planets that might outshine even Sirius, in the same region. In fact, in September 2024, Jupiter is also in the morning sky and definitely outshines our brightest star. Mars is there too, but it’s not as bright as Jupiter or Sirius.

What’s more, sometimes there are bright planets in the evening sky during the northern winter, when Orion and Sirius shine brightly. And those planets, too, might be brighter than the sky’s brightest star. In those cases, how can you be sure the object you’re looking at is Sirius? The constellation Orion is your ticket. No matter where you are, no matter what time of the year it is, Orion’s Belt always points to Sirius.

Orion returned to the morning sky in late July

Orion returned to the sky before dawn in late July and early August. In September, you can easily find this large constellation before sunup. Just look in the eastern part of the sky. You’ll easily notice Orion’s Belt, which consists of a short, straight row of three medium-bright stars.

To find Sirius, draw a line through Orion’s Belt and extend that line toward the horizon. There, you’ll spot Sirius, the sky’s brightest star.

Sirius is in the constellation Canis Major the Greater Dog. It’s often called the Dog Star.

Wide array of bright but slightly fuzzy stars, mostly blue-white but one reddish, over dark landscape.
View at EarthSky Community Photos. | Sergei Timofeevski shared this image from November 13, 2023. Sergei wrote: “The constellation Orion the Hunter and the star Sirius rising just above the eastern horizon in the Anza-Borrego Desert State Park, California.” Thank you, Sergei! Note bright Sirius is on the bottom, and Orion’s Belt pointing to it.

Bottom line: In September 2024, you’ll find the constellation Orion, whose three Belt stars make a short, straight row, in the southeast before dawn. Orion’s Belt points to Sirius, the brightest star of the nighttime sky. Only (some) planets shine brighter.

Help support EarthSky! Check out the EarthSky store for fun astronomy gifts and tools for all ages!

The post Orion’s Belt points to Sirius on September mornings first appeared on EarthSky.



from EarthSky https://ift.tt/RPnfNMi
Aucun commentaire:
Libellés :

How asteroid Phaethon can spawn the Geminid meteors

Phaethon: Space rock venting glowing yellow streamers with bright sun in mid distance.
Artist’s concept of asteroid 3200 Phaethon – parent object of the Geminid meteor shower – near the sun. This asteroid is strange because it has a comet-like tail. But the tail is made of gas and not dust. Image via NASA/ JPL-Caltech/ IPAC.
  • Phaethon is a weird asteroid that behaves like a comet, forming a tail of gas when it passes near the sun.
  • Phaethon is the parent of the Geminid meteors, but it doesn’t seem to be releasing enough dust today to account for the number of meteors we see.
  • The heating and cooling as Phaethon rotates creates a cycle of trapped gases forming new compounds, decomposing, and then the cycle repeats.

By Martin D. Suttle, The Open University

Meet Phaethon, a weird asteroid-comet hybrid

What’s the difference between an asteroid and a comet? A comet is basically a dirty iceball composed of rock and ice. The classic image is of a bright “star” in the night sky with a long curved tail extending into space. This is what happens when they approach the sun and start emitting gases and releasing dust. It normally continues until there’s nothing left but rock or until they fragment into dust.

Asteroids, on the other hand, are primarily just rocks. They might conjure up notions of Han Solo steering the Millennium Falcon through an implausibly dense “asteroid field” to escape a swarm of TIE Fighters, but mostly they just quietly orbit the sun, minding their own business.

Yet these two space objects are not always as mutually exclusive as this would suggest. Let me introduce Phaethon, a “rock comet” that blurs the definitions between asteroid and comet. And let me tell you why it will be worth paying attention to this fascinating object in the coming years.

Phaethon and the Geminid meteor shower

Phaethon was discovered by chance in 1983 by two astronomers at the University of Leicester, Simon Green and John Davies. They came across it orbiting the sun while analyzing images collected by a space telescope called the Infrared Astronomical Satellite (Iras). Soon after, other astronomers recognized that Phaethon is the source of the annual Geminid meteor shower, one of the brightest meteor displays in Earth’s calendar.

Every December, as our planet crosses the dusty trail left behind by Phaethon, we are treated to a brilliant spectacle as its dust grains burn up in our atmosphere. Yet Phaethon’s behavior is unlike that of any other objects responsible for a meteor shower.

Strange behavior

Unlike typical comets that shed substantial amounts of dust when they heat up near the sun, Phaethon doesn’t seem to be releasing enough dust today to account for the Geminids. This absence of significant dust emissions generates an interesting problem.

Phaethon’s orbit brings it extremely close to the sun, much closer than Mercury, our innermost planet. At its closest approach (termed perihelion), its surface temperature reaches extremes of around 730 C (1350 F).

You would expect such intense heat to strip away any volatile materials that exist on Phaethon’s surface. This should either expose fresh, unheated layers and shed huge volumes of dust and gas each time it passes close to the sun, or form a barren crust that protects the volatile-rich interior from further heating, leading to an absence of gas or dust release.

Neither of these processes seem to be occurring, however. Instead, Phaethon continues to exhibit comet-like activity, emitting gas but not an accompanying dust cloud. It’s therefore not shedding layers. So the mystery is why the same crust can still emit volatile gases each time the sun heats it.

Our experiment

I led newly published research aimed at addressing this puzzle by simulating the intense solar heating that Phaethon experiences during its perihelion.

We used chips from a rare group of meteorites called the CM chondrites, which contain clays that scientists believe are similar to Phaethon’s composition. We heated these in an oxygen-free environment multiple times, simulating the hot-cold/day-night cycles that occur on Phaethon when it’s close to the sun.

The results were surprising. Unlike other volatile substances that would typically be lost after a few heating cycles, the small quantities of sulfurous gases contained in the meteorites were released slowly, over many cycles.

This suggests that even after numerous close passes by the sun, Phaethon still has enough gas to generate comet-like activity during each perihelion.

But how might this work? Our theory is that when Phaethon’s surface heats up, iron sulfide minerals held in its subsurface break down into gases, such as sulfur dioxide. However, because the surface layers of Phaethon are relatively impermeable, these gases cannot escape quickly. Instead, they accumulate beneath the surface, for example, in pore spaces and cracks.

As Phaethon rotates, which takes just under four hours, day turns to night and the subsurface cools. Some of the trapped gases are able to “back-react” to form a new generation of compounds. When night turns to day again and heating restarts, these decompose and the cycle repeats.

Why this matters

These findings are not just academic but have implications for the Japanese Space Agency (Jaxa)’s Destiny+ mission, set to launch later this decade. This space probe will fly past Phaethon and study it using two multispectral cameras and a dust analyzer. It will hopefully gather particles that will provide further clues about the composition of this enigmatic object.

How Destiny+ will visit Phaethon:

Either way, our research team’s theory of Phaethon’s gas-emission processes will be crucial for interpreting the data. If we are proven right, it will redefine how scientists think about solar heating as a geological process by making it relevant not only to comets but also to asteroids.

Crucially, Phaethon is not alone. There are about 95 asteroids that pass within 0.20 astronomical units (nearly 19 million miles, or 30 million km) of the sun. Whatever we learn from Phaethon could offer insights into their behavior and long-term stability, too.

Finally, you may be wondering how all this relates to the Geminid meteor shower. Most likely, Phaethon was emitting dust many years ago. This would have produced the debris band that creates the Geminid shower each time the particles come into contact with Earth’s atmosphere. When we talk about gifts that keep on giving, it’s hard to think of a better example.The Conversation

Martin D. Suttle, Lecturer in Planetary Science, The Open University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Phaethon is a weird asteroid that behaves like a comet. It’s also responsible for the Geminid meteor shower. A new study suggests it can supply the meteors through processes that occur during its heating and cooling.

The post How asteroid Phaethon can spawn the Geminid meteors first appeared on EarthSky.



from EarthSky https://ift.tt/HFJQ9KV
Phaethon: Space rock venting glowing yellow streamers with bright sun in mid distance.
Artist’s concept of asteroid 3200 Phaethon – parent object of the Geminid meteor shower – near the sun. This asteroid is strange because it has a comet-like tail. But the tail is made of gas and not dust. Image via NASA/ JPL-Caltech/ IPAC.
  • Phaethon is a weird asteroid that behaves like a comet, forming a tail of gas when it passes near the sun.
  • Phaethon is the parent of the Geminid meteors, but it doesn’t seem to be releasing enough dust today to account for the number of meteors we see.
  • The heating and cooling as Phaethon rotates creates a cycle of trapped gases forming new compounds, decomposing, and then the cycle repeats.

By Martin D. Suttle, The Open University

Meet Phaethon, a weird asteroid-comet hybrid

What’s the difference between an asteroid and a comet? A comet is basically a dirty iceball composed of rock and ice. The classic image is of a bright “star” in the night sky with a long curved tail extending into space. This is what happens when they approach the sun and start emitting gases and releasing dust. It normally continues until there’s nothing left but rock or until they fragment into dust.

Asteroids, on the other hand, are primarily just rocks. They might conjure up notions of Han Solo steering the Millennium Falcon through an implausibly dense “asteroid field” to escape a swarm of TIE Fighters, but mostly they just quietly orbit the sun, minding their own business.

Yet these two space objects are not always as mutually exclusive as this would suggest. Let me introduce Phaethon, a “rock comet” that blurs the definitions between asteroid and comet. And let me tell you why it will be worth paying attention to this fascinating object in the coming years.

Phaethon and the Geminid meteor shower

Phaethon was discovered by chance in 1983 by two astronomers at the University of Leicester, Simon Green and John Davies. They came across it orbiting the sun while analyzing images collected by a space telescope called the Infrared Astronomical Satellite (Iras). Soon after, other astronomers recognized that Phaethon is the source of the annual Geminid meteor shower, one of the brightest meteor displays in Earth’s calendar.

Every December, as our planet crosses the dusty trail left behind by Phaethon, we are treated to a brilliant spectacle as its dust grains burn up in our atmosphere. Yet Phaethon’s behavior is unlike that of any other objects responsible for a meteor shower.

Strange behavior

Unlike typical comets that shed substantial amounts of dust when they heat up near the sun, Phaethon doesn’t seem to be releasing enough dust today to account for the Geminids. This absence of significant dust emissions generates an interesting problem.

Phaethon’s orbit brings it extremely close to the sun, much closer than Mercury, our innermost planet. At its closest approach (termed perihelion), its surface temperature reaches extremes of around 730 C (1350 F).

You would expect such intense heat to strip away any volatile materials that exist on Phaethon’s surface. This should either expose fresh, unheated layers and shed huge volumes of dust and gas each time it passes close to the sun, or form a barren crust that protects the volatile-rich interior from further heating, leading to an absence of gas or dust release.

Neither of these processes seem to be occurring, however. Instead, Phaethon continues to exhibit comet-like activity, emitting gas but not an accompanying dust cloud. It’s therefore not shedding layers. So the mystery is why the same crust can still emit volatile gases each time the sun heats it.

Our experiment

I led newly published research aimed at addressing this puzzle by simulating the intense solar heating that Phaethon experiences during its perihelion.

We used chips from a rare group of meteorites called the CM chondrites, which contain clays that scientists believe are similar to Phaethon’s composition. We heated these in an oxygen-free environment multiple times, simulating the hot-cold/day-night cycles that occur on Phaethon when it’s close to the sun.

The results were surprising. Unlike other volatile substances that would typically be lost after a few heating cycles, the small quantities of sulfurous gases contained in the meteorites were released slowly, over many cycles.

This suggests that even after numerous close passes by the sun, Phaethon still has enough gas to generate comet-like activity during each perihelion.

But how might this work? Our theory is that when Phaethon’s surface heats up, iron sulfide minerals held in its subsurface break down into gases, such as sulfur dioxide. However, because the surface layers of Phaethon are relatively impermeable, these gases cannot escape quickly. Instead, they accumulate beneath the surface, for example, in pore spaces and cracks.

As Phaethon rotates, which takes just under four hours, day turns to night and the subsurface cools. Some of the trapped gases are able to “back-react” to form a new generation of compounds. When night turns to day again and heating restarts, these decompose and the cycle repeats.

Why this matters

These findings are not just academic but have implications for the Japanese Space Agency (Jaxa)’s Destiny+ mission, set to launch later this decade. This space probe will fly past Phaethon and study it using two multispectral cameras and a dust analyzer. It will hopefully gather particles that will provide further clues about the composition of this enigmatic object.

How Destiny+ will visit Phaethon:

Either way, our research team’s theory of Phaethon’s gas-emission processes will be crucial for interpreting the data. If we are proven right, it will redefine how scientists think about solar heating as a geological process by making it relevant not only to comets but also to asteroids.

Crucially, Phaethon is not alone. There are about 95 asteroids that pass within 0.20 astronomical units (nearly 19 million miles, or 30 million km) of the sun. Whatever we learn from Phaethon could offer insights into their behavior and long-term stability, too.

Finally, you may be wondering how all this relates to the Geminid meteor shower. Most likely, Phaethon was emitting dust many years ago. This would have produced the debris band that creates the Geminid shower each time the particles come into contact with Earth’s atmosphere. When we talk about gifts that keep on giving, it’s hard to think of a better example.The Conversation

Martin D. Suttle, Lecturer in Planetary Science, The Open University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Phaethon is a weird asteroid that behaves like a comet. It’s also responsible for the Geminid meteor shower. A new study suggests it can supply the meteors through processes that occur during its heating and cooling.

The post How asteroid Phaethon can spawn the Geminid meteors first appeared on EarthSky.



from EarthSky https://ift.tt/HFJQ9KV
Aucun commentaire:
Libellés :

Deep-sky photos for August 2024: Editor’s picks

Deep-sky photos: A bright, large and reddish heart-shaped nebulosity over a multitude of distant stars.
View at EarthSky Community Photos. | Catherine Hyde in Shandon, California, captured IC 1805, the Heart Nebula, on August 3, 2024. Catherine wrote: “This is the Heart Nebula in the constellation Cassiopeia. I took images from 9:30 at night until almost 5:00 in the morning.” An outstanding image. Thank you, Catherine! See more deep-sky photos from August below.

Stunning deep-sky photos from our community

The EarthSky community has many talented astrophotographers who capture stunning images of the deep sky. We gathered some of our favorite deep-sky photos we received in August 2024 for you to enjoy. Do you have some of your own deep-sky images to share? You can submit them to us here. We love to see them!

Deep-sky photos of diffuse nebulae

Prolific swirls of red purple nebulosity over a background of distant stars.
View at EarthSky Community Photos. | Andrea Iorio in Marino, Rome, Italy, made this mosaic of the Veil Nebula on August 10, 2024. Andrea wrote: “This is the remains of a massive star that exploded about 8,000 years ago. Called the Veil Nebula, the debris is one of the best-known supernova remnants, deriving its name from its delicate, draped, filamentary structures. The entire nebula is 110 light-years across, covering six full moons on the sky as seen from Earth. It resides about 2,100 light-years away in the constellation Cygnus the Swan.” Thank you, Andrea!
A bright white star surrounded by wisps of reddish gas and a nultitude of field stars.
View at EarthSky Community Photos. | Kris Hazelbaker in Grangeville, Idaho, captured IC 63, the Ghost of Cassiopeia, on August 29, 2024. Kris wrote: “I aimed my gear at this target over 2 nights. It’s an area that has always interested me, and I’m really happy with how this turned out.” Wonderful shot. Thank you, Kris!
A bright blue, nebulous region with dark lanes, over a rich background of stars.
View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured this view in the constellation Cepheus on August 26, 2024. It contains the Iris Nebula and nearby dark clouds. Andy wrote: “They say there are always lots of failures in astrophotography. It has been nonstop for me, but last night, like the 2 previous nights, I just went outside, set up and took pics. Getting pics like this makes it all worth it. Space is so cool!” Indeed it is! Thank you, Andy.

The Crescent Nebula

A small and bright, reddish cocoon of gas overlaid with prolific red clouds and numerous stars.
View at EarthSky Community Photos. | Isaac Cruz in Reynoldsburg, Ohio, captured the Crescent Nebula on August 21, 2024. Isaac wrote: “This is a long-exposure image of the Crescent Nebula (NGC 6888) in the constellation Cygnus,The Soap Bubble Nebula is in the lower-left quadrant.” Spectacular image. Thank you, Isaac!
A large, pink cocoon of gas overlaid with prolific red clouds and numerous stars.
View at EarthSky Community Photos. | Andrea Iorio in Marino, Rome, Italy, caught the Crescent Nebula on August 30, 2024. Andrea wrote: “The Crescent Nebula is about 25 light-years across. Visible within the nebula, the central star is a Wolf-Rayet star (WR 136). It’s shedding its outer envelope in a strong stellar wind, ejecting the equivalent of the sun’s mass every 10,000 years. The nebula’s complex structures are likely the result of this strong wind interacting with material ejected in an earlier phase. This star should ultimately go out with a bang in a spectacular supernova explosion.” Thank you, Andrea!

The Elephant’s Trunk Nebula

A bright red, nebulous region with dark lanes, over a rich background of stars.
View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured the Elephant’s Trunk Nebula in the constellation Cepheus on August 27, 2024. Andy wrote: “The Elephant’s Trunk Nebula in Cepheus. This was my second night in row of finally having less clouds and less moon. There was enough moonless time for 26 10-minute shots. What a joy to finally have my new gear working. I used 100% of the shots I took!” Thank you, Andy!
A bright red, nebulous region with dark lanes, over a rich background of stars.
View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, again went on to image the Elephant’s Trunk Nebula – this time using a larger telescope to capture deeper detail – on August 31, 2024. Andy wrote: “A few days ago I took a wide-field pic of the Elephant’s Trunk Nebula. This pic is zoomed into the trunk only. What fun it is to see the big and the small!” Thank you, Andy!

Deep-sky photos of the Dumbbell Nebula

Dumbbell-shaped cloud of reddish and green nebulosity over a background of distant stars.
View at EarthSky Community Photos. | Kris Hazelbaker in Grangeville, Idaho, captured the Dumbbell Nebula on August 1, 2024. Kris wrote: “The Dumbbell Nebula, M27, is in the constellation Vulpecula, which straddles the Milky Way. I took just over 3 hours of 3-minute exposures to make this final image.” Thank you, Kris!
Dumbbell-shaped cloud of reddish and blue nebulosity over a background of distant stars.
View at EarthSky Community Photos. | Catherine Hyde in Cambria, California, captured the Dumbbell Nebula on August 5, 2024. Catherine wrote: “This is M27, the Dumbbell Nebula in the constellation Vulpecula.” Thank you, Catherine!

A globular cluster

A large, spherical cluster containing thousands of bright stars.
View at EarthSky Community Photos. | Mario Rana in Hampton, Virginia, used an astrograph to capture this view of the globular cluster Messier 22 in the constellation Sagittarius on August 22, 2024. Thank you, Mario!

… and the Andromeda Galaxy

Large whitish nebula with a bright nucleus, dark lanes and thousands of foreground stars.
View at EarthSky Community Photos. | Russell Owens in Reno, Nevada, captured the Andromeda galaxy on August 27, 2024. Thank you, Russell!

Bottom line: Enjoy this gallery of deep-sky photos for August 2024 from our EarthSky community. If you have a great photo to share, send it in too. We love to see them!

Share your recent Earth or sky photo at EarthSky Community Photos.

The post Deep-sky photos for August 2024: Editor’s picks first appeared on EarthSky.



from EarthSky https://ift.tt/tWC3I0p
Deep-sky photos: A bright, large and reddish heart-shaped nebulosity over a multitude of distant stars.
View at EarthSky Community Photos. | Catherine Hyde in Shandon, California, captured IC 1805, the Heart Nebula, on August 3, 2024. Catherine wrote: “This is the Heart Nebula in the constellation Cassiopeia. I took images from 9:30 at night until almost 5:00 in the morning.” An outstanding image. Thank you, Catherine! See more deep-sky photos from August below.

Stunning deep-sky photos from our community

The EarthSky community has many talented astrophotographers who capture stunning images of the deep sky. We gathered some of our favorite deep-sky photos we received in August 2024 for you to enjoy. Do you have some of your own deep-sky images to share? You can submit them to us here. We love to see them!

Deep-sky photos of diffuse nebulae

Prolific swirls of red purple nebulosity over a background of distant stars.
View at EarthSky Community Photos. | Andrea Iorio in Marino, Rome, Italy, made this mosaic of the Veil Nebula on August 10, 2024. Andrea wrote: “This is the remains of a massive star that exploded about 8,000 years ago. Called the Veil Nebula, the debris is one of the best-known supernova remnants, deriving its name from its delicate, draped, filamentary structures. The entire nebula is 110 light-years across, covering six full moons on the sky as seen from Earth. It resides about 2,100 light-years away in the constellation Cygnus the Swan.” Thank you, Andrea!
A bright white star surrounded by wisps of reddish gas and a nultitude of field stars.
View at EarthSky Community Photos. | Kris Hazelbaker in Grangeville, Idaho, captured IC 63, the Ghost of Cassiopeia, on August 29, 2024. Kris wrote: “I aimed my gear at this target over 2 nights. It’s an area that has always interested me, and I’m really happy with how this turned out.” Wonderful shot. Thank you, Kris!
A bright blue, nebulous region with dark lanes, over a rich background of stars.
View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured this view in the constellation Cepheus on August 26, 2024. It contains the Iris Nebula and nearby dark clouds. Andy wrote: “They say there are always lots of failures in astrophotography. It has been nonstop for me, but last night, like the 2 previous nights, I just went outside, set up and took pics. Getting pics like this makes it all worth it. Space is so cool!” Indeed it is! Thank you, Andy.

The Crescent Nebula

A small and bright, reddish cocoon of gas overlaid with prolific red clouds and numerous stars.
View at EarthSky Community Photos. | Isaac Cruz in Reynoldsburg, Ohio, captured the Crescent Nebula on August 21, 2024. Isaac wrote: “This is a long-exposure image of the Crescent Nebula (NGC 6888) in the constellation Cygnus,The Soap Bubble Nebula is in the lower-left quadrant.” Spectacular image. Thank you, Isaac!
A large, pink cocoon of gas overlaid with prolific red clouds and numerous stars.
View at EarthSky Community Photos. | Andrea Iorio in Marino, Rome, Italy, caught the Crescent Nebula on August 30, 2024. Andrea wrote: “The Crescent Nebula is about 25 light-years across. Visible within the nebula, the central star is a Wolf-Rayet star (WR 136). It’s shedding its outer envelope in a strong stellar wind, ejecting the equivalent of the sun’s mass every 10,000 years. The nebula’s complex structures are likely the result of this strong wind interacting with material ejected in an earlier phase. This star should ultimately go out with a bang in a spectacular supernova explosion.” Thank you, Andrea!

The Elephant’s Trunk Nebula

A bright red, nebulous region with dark lanes, over a rich background of stars.
View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, captured the Elephant’s Trunk Nebula in the constellation Cepheus on August 27, 2024. Andy wrote: “The Elephant’s Trunk Nebula in Cepheus. This was my second night in row of finally having less clouds and less moon. There was enough moonless time for 26 10-minute shots. What a joy to finally have my new gear working. I used 100% of the shots I took!” Thank you, Andy!
A bright red, nebulous region with dark lanes, over a rich background of stars.
View at EarthSky Community Photos. | Andy Dungan near Cotopaxi, Colorado, again went on to image the Elephant’s Trunk Nebula – this time using a larger telescope to capture deeper detail – on August 31, 2024. Andy wrote: “A few days ago I took a wide-field pic of the Elephant’s Trunk Nebula. This pic is zoomed into the trunk only. What fun it is to see the big and the small!” Thank you, Andy!

Deep-sky photos of the Dumbbell Nebula

Dumbbell-shaped cloud of reddish and green nebulosity over a background of distant stars.
View at EarthSky Community Photos. | Kris Hazelbaker in Grangeville, Idaho, captured the Dumbbell Nebula on August 1, 2024. Kris wrote: “The Dumbbell Nebula, M27, is in the constellation Vulpecula, which straddles the Milky Way. I took just over 3 hours of 3-minute exposures to make this final image.” Thank you, Kris!
Dumbbell-shaped cloud of reddish and blue nebulosity over a background of distant stars.
View at EarthSky Community Photos. | Catherine Hyde in Cambria, California, captured the Dumbbell Nebula on August 5, 2024. Catherine wrote: “This is M27, the Dumbbell Nebula in the constellation Vulpecula.” Thank you, Catherine!

A globular cluster

A large, spherical cluster containing thousands of bright stars.
View at EarthSky Community Photos. | Mario Rana in Hampton, Virginia, used an astrograph to capture this view of the globular cluster Messier 22 in the constellation Sagittarius on August 22, 2024. Thank you, Mario!

… and the Andromeda Galaxy

Large whitish nebula with a bright nucleus, dark lanes and thousands of foreground stars.
View at EarthSky Community Photos. | Russell Owens in Reno, Nevada, captured the Andromeda galaxy on August 27, 2024. Thank you, Russell!

Bottom line: Enjoy this gallery of deep-sky photos for August 2024 from our EarthSky community. If you have a great photo to share, send it in too. We love to see them!

Share your recent Earth or sky photo at EarthSky Community Photos.

The post Deep-sky photos for August 2024: Editor’s picks first appeared on EarthSky.



from EarthSky https://ift.tt/tWC3I0p
Aucun commentaire:
Libellés :

Earth’s core has a huge, hidden donut shape

Cutaway showing graphic of inside of Earth with red for inner core, blue for outer core and a red band for the donut.
This artist’s concept of the Earth’s core shows the inner core in red, the outer core in blue, and the donut in red. The donut region contains more light elements around the equator. Image via Xiaolong Ma and Hrvoje Tkalcic/ The Conversation.
  • Earth’s core is in two parts, an inner solid core and a liquid outer core.
  • Scientists just discovered a large donut-shaped region within the outer core. They used a new method of measuring seismic waves to find it.
  • Earth’s magnetic field is powered by the liquid outer core. The discovery provides new clues about the dynamics of the magnetic field.

New discovery from Earth’s interior

We think of Earth’s interior as being rather simple, with the mantle surrounding an inner core. It’s a bit more complex than that, though. There is an inner core, which is solid, and an outer core, which is liquid. And now, scientists have discovered a donut-shaped region on top of the outer core. On September 3, 2024, researchers at Australian National University said they found the donut-shaped feature by analyzing seismic waves passing through the core. The donut rests on top of the outer liquid core, where the core meets the mantle.

The seismic waves move 2% slower through this donut region. Geophysicist Hrvoje Tkalcic and Xiaolong Ma led the new study about Earth’s core. Tkalcic wrote in The Conversation:

We think this region contains more lighter elements such as silicon and oxygen, and may play a crucial role in the vast currents of liquid metal running through the core that generate Earth’s magnetic field.

The scientists published their peer-reviewed findings in Science Advances on August 30, 2024.

A giant donut in Earth’s core

The researchers discovered the donut-shaped region by studying how seismic waves move through Earth’s core. They found the waves moved slower through the donut than the rest of the outer core. This made it possible to map out the shape, size and location of the donut.

The donut sits on top of the outer liquid core. This is where the liquid core comes into contact with the surrounding mantle. Tkalcic also said:

The region sits parallel to the equatorial plane, is confined to the low latitudes and has a doughnut shape. We don’t know the exact thickness of the donut, but we inferred that it reaches a few hundred kilometers beneath the core-mantle boundary.

The donut feature had remained undetected until now, the researchers said.

Earth's core: Earth sphere separated into sections for crust, mantle and core, in space. Center core sphere is very bright.
An artist’s depiction of Earth’s structure, separated into crust, mantle, outer core and inner core. Scientists have now discovered a huge donut-shaped region in Earth’s core. The donut sits deep in the liquid outer core at low latitudes, parallel to the equator. Image via Shad.off/ Depositphotos (Royalty-Free).

A new way to measure seismic waves

The researchers measured seismic waves – like those generated by earthquakes – to make the discovery. For this study, however, they took a bit of a different approach. Usually, scientists will study the seismic signals within the first hour after an earthquake. But this time, they waited until hours later. This revealed the low speed of the waves through part of the outer core. Tkalcic explained:

By understanding the geometry of the paths of the waves and how they traverse the outer core’s volume, we reconstructed their travel times through the Earth, demonstrating that the newly discovered region has low seismic speeds.

The peculiar structure remained hidden until now as previous studies collected data with less volumetric coverage of the outer core by observing waves that were typically confined within one hour after the origin times of large earthquakes.

We were able to achieve much better volumetric coverage because we studied the reverberating waves for many hours after large earthquakes.

Cut-away view of Earth with bright white center and white text labels on black background.
The Earth’s interior consists of the upper mantle, mantle outer core and inner core. Image via NASA (Adapted from Goddard Media Studios).

Mysteries of the Earth’s core and magnetic field

The discovery of the donut will help scientists solve mysteries about both Earth’s core and magnetic field. Ma said:

There are still mysteries about the Earth’s outer core that are yet to be solved, which requires multidisciplinary efforts from seismology, mineral physics, geomagnetism and geodynamics.

As Tkalcic also noted:

Our findings are interesting because this low velocity within the liquid core implies that we have a high concentration of light chemical elements in these regions that would cause the seismic waves to slow down. These light elements, alongside temperature differences, help stir liquid in the outer core.

In addition, the composition of the outer core is directly tied to the behavior of the magnetic field. Understanding this better will help scientists know when it might weaken. And that, of course, is essential, since the magnetic field helps to protect all life on Earth from dangerous radiation coming from the sun. Tkalcic said:

The magnetic field is a fundamental ingredient that we need for life to be sustained on the surface of our planet.

The dynamics of Earth’s magnetic field is an area of strong interest in the scientific community, so our results could promote more research about the magnetic field on both Earth and other planets.

Bottom line: Scientists in Australia have discovered a huge donut-shaped region in Earth’s core. The finding provides new clues about the dynamics of Earth’s magnetic field.

Source: Seismic low-velocity equatorial torus in the Earth’s outer core: Evidence from the late–coda correlation wavefield

Via Australian National University

Read more: Earth’s lopsided core? Strangeness in our planet’s interior

Read more: Surprise! Earth’s core has a core

The post Earth’s core has a huge, hidden donut shape first appeared on EarthSky.



from EarthSky https://ift.tt/nVY8NIP
Cutaway showing graphic of inside of Earth with red for inner core, blue for outer core and a red band for the donut.
This artist’s concept of the Earth’s core shows the inner core in red, the outer core in blue, and the donut in red. The donut region contains more light elements around the equator. Image via Xiaolong Ma and Hrvoje Tkalcic/ The Conversation.
  • Earth’s core is in two parts, an inner solid core and a liquid outer core.
  • Scientists just discovered a large donut-shaped region within the outer core. They used a new method of measuring seismic waves to find it.
  • Earth’s magnetic field is powered by the liquid outer core. The discovery provides new clues about the dynamics of the magnetic field.

New discovery from Earth’s interior

We think of Earth’s interior as being rather simple, with the mantle surrounding an inner core. It’s a bit more complex than that, though. There is an inner core, which is solid, and an outer core, which is liquid. And now, scientists have discovered a donut-shaped region on top of the outer core. On September 3, 2024, researchers at Australian National University said they found the donut-shaped feature by analyzing seismic waves passing through the core. The donut rests on top of the outer liquid core, where the core meets the mantle.

The seismic waves move 2% slower through this donut region. Geophysicist Hrvoje Tkalcic and Xiaolong Ma led the new study about Earth’s core. Tkalcic wrote in The Conversation:

We think this region contains more lighter elements such as silicon and oxygen, and may play a crucial role in the vast currents of liquid metal running through the core that generate Earth’s magnetic field.

The scientists published their peer-reviewed findings in Science Advances on August 30, 2024.

A giant donut in Earth’s core

The researchers discovered the donut-shaped region by studying how seismic waves move through Earth’s core. They found the waves moved slower through the donut than the rest of the outer core. This made it possible to map out the shape, size and location of the donut.

The donut sits on top of the outer liquid core. This is where the liquid core comes into contact with the surrounding mantle. Tkalcic also said:

The region sits parallel to the equatorial plane, is confined to the low latitudes and has a doughnut shape. We don’t know the exact thickness of the donut, but we inferred that it reaches a few hundred kilometers beneath the core-mantle boundary.

The donut feature had remained undetected until now, the researchers said.

Earth's core: Earth sphere separated into sections for crust, mantle and core, in space. Center core sphere is very bright.
An artist’s depiction of Earth’s structure, separated into crust, mantle, outer core and inner core. Scientists have now discovered a huge donut-shaped region in Earth’s core. The donut sits deep in the liquid outer core at low latitudes, parallel to the equator. Image via Shad.off/ Depositphotos (Royalty-Free).

A new way to measure seismic waves

The researchers measured seismic waves – like those generated by earthquakes – to make the discovery. For this study, however, they took a bit of a different approach. Usually, scientists will study the seismic signals within the first hour after an earthquake. But this time, they waited until hours later. This revealed the low speed of the waves through part of the outer core. Tkalcic explained:

By understanding the geometry of the paths of the waves and how they traverse the outer core’s volume, we reconstructed their travel times through the Earth, demonstrating that the newly discovered region has low seismic speeds.

The peculiar structure remained hidden until now as previous studies collected data with less volumetric coverage of the outer core by observing waves that were typically confined within one hour after the origin times of large earthquakes.

We were able to achieve much better volumetric coverage because we studied the reverberating waves for many hours after large earthquakes.

Cut-away view of Earth with bright white center and white text labels on black background.
The Earth’s interior consists of the upper mantle, mantle outer core and inner core. Image via NASA (Adapted from Goddard Media Studios).

Mysteries of the Earth’s core and magnetic field

The discovery of the donut will help scientists solve mysteries about both Earth’s core and magnetic field. Ma said:

There are still mysteries about the Earth’s outer core that are yet to be solved, which requires multidisciplinary efforts from seismology, mineral physics, geomagnetism and geodynamics.

As Tkalcic also noted:

Our findings are interesting because this low velocity within the liquid core implies that we have a high concentration of light chemical elements in these regions that would cause the seismic waves to slow down. These light elements, alongside temperature differences, help stir liquid in the outer core.

In addition, the composition of the outer core is directly tied to the behavior of the magnetic field. Understanding this better will help scientists know when it might weaken. And that, of course, is essential, since the magnetic field helps to protect all life on Earth from dangerous radiation coming from the sun. Tkalcic said:

The magnetic field is a fundamental ingredient that we need for life to be sustained on the surface of our planet.

The dynamics of Earth’s magnetic field is an area of strong interest in the scientific community, so our results could promote more research about the magnetic field on both Earth and other planets.

Bottom line: Scientists in Australia have discovered a huge donut-shaped region in Earth’s core. The finding provides new clues about the dynamics of Earth’s magnetic field.

Source: Seismic low-velocity equatorial torus in the Earth’s outer core: Evidence from the late–coda correlation wavefield

Via Australian National University

Read more: Earth’s lopsided core? Strangeness in our planet’s interior

Read more: Surprise! Earth’s core has a core

The post Earth’s core has a huge, hidden donut shape first appeared on EarthSky.



from EarthSky https://ift.tt/nVY8NIP
Aucun commentaire:
Libellés :
Inscription à : Articles (Atom)