Why Nile hasn’t changed course in 30 million years

The Nile River in Cairo, Egypt. Image via Nina R./University of Texas.

The steady northward path of the Nile River – stretching over 4,225 miles (6,800 km) – has nourished the fertile valleys of northeast Africa for millions of years, and is still important for irrigation and transportation. For scientists, however, the Nile’s path has been a geologic mystery. That’s because long-lived rivers usually change course over time. Why has the northward course of the Nile remained so steady for millions of years?

A new study suggests that the river would’ve changed course westward many, many years ago if it weren’t for the movement of rock in the Earth’s deep mantle keeping the Nile on course. The Earth’s mantle is composed of solid rock that flows like a fluid over long periods. Like currents in an ocean, different areas of the mantle have different circulation patterns.

University of Texas geologist Claudio Faccenna is lead author of the paper, published November 11, 2019, in the journal Nature Geoscience. Faccenna said in a statement:

One of the big questions about the Nile is when it originated and why it has persisted for so long.

In the course of their investigation, the researchers also found the river to be 30 million years old – about 6 times older than previously thought.

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Image via Wikipedia.

In the paper, the researchers connected the tilted nature of the Nile’s topography (the arrangement of an area’s physical features) to a conveyor belt of mantle rock pushing up against the Ethiopian Highlands in the south and pulling the surface down in the north. From beginning to end, the gentle gradient keeps the Nile on a consistent northward course.

The research team traced the Nile’s geological history by studying ancient volcanic rock in the Ethiopian Highlands and correlating it with enormous deposits of river sediment buried under the Nile Delta. Their analysis suggested that after rising dramatically, the Ethiopian Highlands have remained at a similar height for millions of years, which the researchers attribute to the support of the mantle rock from below.

Thorsten Becker is a University of Texas geologist and co-author of the study. He said:

We know that the high topography of the Ethiopian plateau was formed about 30 million years ago.

Until now, however, it was unclear how this topography has been maintained for so long.

The team verified their findings using computer simulations that re-created 40 million years of Earth’s plate tectonic activity. The model suggested that a hot mantle plume probably led to the outpouring of lava that formed the Ethiopian Highlands, while activating a conveyor belt in the mantle that persists today.

Image via Getty Images/Futurity.

Bottom line: A new study suggest the reason the Nile River has maintained its northward course for so long, as well as a new estimate for the river’s age.

Source: Role of dynamic topography in sustaining the Nile River over 30 million years

Via University of Texas at Austin

from EarthSky https://ift.tt/2XtZH3U

The Nile River in Cairo, Egypt. Image via Nina R./University of Texas.

The steady northward path of the Nile River – stretching over 4,225 miles (6,800 km) – has nourished the fertile valleys of northeast Africa for millions of years, and is still important for irrigation and transportation. For scientists, however, the Nile’s path has been a geologic mystery. That’s because long-lived rivers usually change course over time. Why has the northward course of the Nile remained so steady for millions of years?

A new study suggests that the river would’ve changed course westward many, many years ago if it weren’t for the movement of rock in the Earth’s deep mantle keeping the Nile on course. The Earth’s mantle is composed of solid rock that flows like a fluid over long periods. Like currents in an ocean, different areas of the mantle have different circulation patterns.

University of Texas geologist Claudio Faccenna is lead author of the paper, published November 11, 2019, in the journal Nature Geoscience. Faccenna said in a statement:

One of the big questions about the Nile is when it originated and why it has persisted for so long.

In the course of their investigation, the researchers also found the river to be 30 million years old – about 6 times older than previously thought.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Image via Wikipedia.

In the paper, the researchers connected the tilted nature of the Nile’s topography (the arrangement of an area’s physical features) to a conveyor belt of mantle rock pushing up against the Ethiopian Highlands in the south and pulling the surface down in the north. From beginning to end, the gentle gradient keeps the Nile on a consistent northward course.

The research team traced the Nile’s geological history by studying ancient volcanic rock in the Ethiopian Highlands and correlating it with enormous deposits of river sediment buried under the Nile Delta. Their analysis suggested that after rising dramatically, the Ethiopian Highlands have remained at a similar height for millions of years, which the researchers attribute to the support of the mantle rock from below.

Thorsten Becker is a University of Texas geologist and co-author of the study. He said:

We know that the high topography of the Ethiopian plateau was formed about 30 million years ago.

Until now, however, it was unclear how this topography has been maintained for so long.

The team verified their findings using computer simulations that re-created 40 million years of Earth’s plate tectonic activity. The model suggested that a hot mantle plume probably led to the outpouring of lava that formed the Ethiopian Highlands, while activating a conveyor belt in the mantle that persists today.

Image via Getty Images/Futurity.

Bottom line: A new study suggest the reason the Nile River has maintained its northward course for so long, as well as a new estimate for the river’s age.

Source: Role of dynamic topography in sustaining the Nile River over 30 million years

Via University of Texas at Austin

from EarthSky https://ift.tt/2XtZH3U

Who knew? Plants ‘panic’ when it rains

Here on Earth at least, all living things need water. So the results of new research from an international team of scientists seems surprising: plants don’t like getting wet. These scientists measured a “panic” response in plants in response to showers of water. The intriguing, peer-reviewed results are published in the October 29, 2019, issue of the Proceedings of the National Academy of Sciences.

Biochemist Harvey Millar of the University of Western Australia is featured in the video above. He said:

In the future, we’ll really be able to understand how plants are coping with rain, because rain can bring disease. It can bring a whole variety of other factors, which affect plants …

We’ll be able to equip plants to interact with their environment in a different way than they do at the moment.

Millar explained that the disease-carrying aspect of rain appears to be a major factor for plants:

When a raindrop splashes across a leaf, tiny droplets of water ricochet in all directions. These droplets can contain bacteria, viruses, or fungal spores. A single droplet can spread these up to 10 meters (32 feet) to surrounding plants.

The researchers used a spray bottle to simulate rain. They found that, after 10 minutes, over 700 genes in the plants they studied reacted in a “panic-like” manner and continued to do so for about 15 minutes. The response was rapid, even from just a single touch of water, these scientists said. The response affected chemical reactions in the plants, such as their hormone balance and how they create proteins. Warning signals were sent from leaf to leaf in the plants, with the plants ultimately taking defensive measures against the water. Plants that received repeated waterings had stunted growth and delayed flowering.

One of the most interesting reactions involved the plants “communicating” their fears or stress with other nearby plants. They communicate via the release of airborne chemicals that can travel to other plants. As Millar said:

If a plant’s neighbors have their defense mechanisms turned on, they are less likely to spread disease so it’s in their best interest for plants to spread the warning to nearby plants.

It all sounds like science fiction. But these results build on what scientists already knew about how plants can react to their surroundings and communicate with each other in their own way. Plants can also respond to and warn each other about other dangers, for example insects. Consider aphid-infested bean plants that release odorous chemicals called volatile organic compounds (VOCs) into the air. Neighboring bean plants respond by emitting different VOCs that repel the aphids and attract aphid-hunting wasps.

And those same plants communicated in another way as well. They used symbiont fungi – mycorrhizal fungi connecting the roots of the plants with the hyphae, branching filaments that make up the fungal mycelium – to send chemical warnings below the surface. As David Johnson, a soil ecologist at the University of Aberdeen noted that when his team first saw these results:

… it was quite a eureka moment … We had more samples to test, but even at that point, it was pretty clear that this is an effective signaling system.

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Plants can communicate with each other about possible dangers, including water-borne disease or insects. Image via Pop_Jop/iStockPhoto.com/The Scientist.

It even seems that plants can “eavesdrop” on hints of their neighboring plants’ distress through their root systems.

They might be able to communicate through ultrasonic sounds – any sounds above the frequency of audible sound – further evidence that they can communicate in more ways than ever thought possible. According to Richard Karban, an evolutionary ecologist at the University of California, Davis:

In the last 15 years the idea that plants are communicating has become much more accepted. The evidence for that is now substantial, and it’s exciting to unravel all these different realms of plant communication.

Monica Gagliano, an evolutionary ecologist at the University of Western Australia, found that the roots of young corn plants grown in water make clicking sounds, and that when sounds in the same frequency range were played back to the roots, they responded by bending toward the source. Gagliano said:

We’ve shown that plants can recognize when they’re growing next to a ‘bad neighbor’ and change their growth behavior accordingly, even when we remove all the channels of communication we know about. We also have some evidence that there is an emission [of sound] and a response of some sort. We are not ruling out other possibilities, of course, but we think this other channel of communication might be acoustic.

Image via an article on gardening in the rain, from Gardening-ABC.com

Bottom line: Even though plants need water, new research shows that they panic about getting wet and can communicate about this and other perceived dangers.

Source: A MYC2/MYC3/MYC4-dependent transcription factor network regulates water spray-responsive gene expression and jasmonate levels

Via Phys.org

from EarthSky https://ift.tt/2D8RDMN

Here on Earth at least, all living things need water. So the results of new research from an international team of scientists seems surprising: plants don’t like getting wet. These scientists measured a “panic” response in plants in response to showers of water. The intriguing, peer-reviewed results are published in the October 29, 2019, issue of the Proceedings of the National Academy of Sciences.

Biochemist Harvey Millar of the University of Western Australia is featured in the video above. He said:

In the future, we’ll really be able to understand how plants are coping with rain, because rain can bring disease. It can bring a whole variety of other factors, which affect plants …

We’ll be able to equip plants to interact with their environment in a different way than they do at the moment.

Millar explained that the disease-carrying aspect of rain appears to be a major factor for plants:

When a raindrop splashes across a leaf, tiny droplets of water ricochet in all directions. These droplets can contain bacteria, viruses, or fungal spores. A single droplet can spread these up to 10 meters (32 feet) to surrounding plants.

The researchers used a spray bottle to simulate rain. They found that, after 10 minutes, over 700 genes in the plants they studied reacted in a “panic-like” manner and continued to do so for about 15 minutes. The response was rapid, even from just a single touch of water, these scientists said. The response affected chemical reactions in the plants, such as their hormone balance and how they create proteins. Warning signals were sent from leaf to leaf in the plants, with the plants ultimately taking defensive measures against the water. Plants that received repeated waterings had stunted growth and delayed flowering.

One of the most interesting reactions involved the plants “communicating” their fears or stress with other nearby plants. They communicate via the release of airborne chemicals that can travel to other plants. As Millar said:

If a plant’s neighbors have their defense mechanisms turned on, they are less likely to spread disease so it’s in their best interest for plants to spread the warning to nearby plants.

It all sounds like science fiction. But these results build on what scientists already knew about how plants can react to their surroundings and communicate with each other in their own way. Plants can also respond to and warn each other about other dangers, for example insects. Consider aphid-infested bean plants that release odorous chemicals called volatile organic compounds (VOCs) into the air. Neighboring bean plants respond by emitting different VOCs that repel the aphids and attract aphid-hunting wasps.

And those same plants communicated in another way as well. They used symbiont fungi – mycorrhizal fungi connecting the roots of the plants with the hyphae, branching filaments that make up the fungal mycelium – to send chemical warnings below the surface. As David Johnson, a soil ecologist at the University of Aberdeen noted that when his team first saw these results:

… it was quite a eureka moment … We had more samples to test, but even at that point, it was pretty clear that this is an effective signaling system.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Plants can communicate with each other about possible dangers, including water-borne disease or insects. Image via Pop_Jop/iStockPhoto.com/The Scientist.

It even seems that plants can “eavesdrop” on hints of their neighboring plants’ distress through their root systems.

They might be able to communicate through ultrasonic sounds – any sounds above the frequency of audible sound – further evidence that they can communicate in more ways than ever thought possible. According to Richard Karban, an evolutionary ecologist at the University of California, Davis:

In the last 15 years the idea that plants are communicating has become much more accepted. The evidence for that is now substantial, and it’s exciting to unravel all these different realms of plant communication.

Monica Gagliano, an evolutionary ecologist at the University of Western Australia, found that the roots of young corn plants grown in water make clicking sounds, and that when sounds in the same frequency range were played back to the roots, they responded by bending toward the source. Gagliano said:

We’ve shown that plants can recognize when they’re growing next to a ‘bad neighbor’ and change their growth behavior accordingly, even when we remove all the channels of communication we know about. We also have some evidence that there is an emission [of sound] and a response of some sort. We are not ruling out other possibilities, of course, but we think this other channel of communication might be acoustic.

Image via an article on gardening in the rain, from Gardening-ABC.com

Bottom line: Even though plants need water, new research shows that they panic about getting wet and can communicate about this and other perceived dangers.

Source: A MYC2/MYC3/MYC4-dependent transcription factor network regulates water spray-responsive gene expression and jasmonate levels

Via Phys.org

from EarthSky https://ift.tt/2D8RDMN

Come to know the Pleiades, or 7 Sisters

Image at top: A laser pointer aims up past the V-shaped face of Taurus the Bull, toward the tiny, misty dipper of the Pleiades. Photo by Krishnan Subramanian near Mumbai, India.

Tonight, look for the tiny, misty dipper of stars known as the Pleiades or Seven Sisters. November is the month of the Pleiades star cluster. On these November nights, the Pleiades cluster shines from nightfall until dawn. It’s low in the east at nightfall, high overhead around midnight and low in the west before dawn. Locate it by the bright star Aldebaran this evening, or any evening soon.

The 2020 lunar calendars are here! Order yours before they’re gone. Makes a great gift.

You can view the Pleiades with either the unaided eye or an optical aid on these November nights. The Pleiades cluster is one of the most recognizable star patterns in the night sky. Its six brightest stars do look like a little dipper. In fact, people in the Northern Hemisphere often mistake the Pleiades for the real Little Dipper asterism, which is located farther north on the sky’s dome. The misty-looking dipper of the Pleiades hovers over the northeastern horizon as darkness falls. It moves across the night sky from east to west, much like the sun does during the day.

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EarthSky community member Greg Hogan captured this image of the Pleiades in November 2015.

By the way, another name for the Pleiades is the Seven Sisters. But if you look with your eye alone, it’s likely you’ll only see six stars in the Pleiades. Some old Greek legends explore what might have happened to the missing sister, sometimes called the Lost Pleiad.

In the Northern Hemisphere, the Pleiades’ all-night appearance coincides with late autumn. As this part of the world moves toward winter, it’s easy to imagine the Pleiades as a frosty patch on the dome of night. But in the Southern Hemisphere now, where spring flowers are blooming, this cluster of nocturnal suns watches over the season of awakening and agriculture. In South Africa, for example, the Pleiades are called the hoeing-stars.

Yearly, on or near November 21, the Pleiades cluster culminates – reaches its highest point in the sky – at midnight. (In this instance, midnight means midway between sunset and sunrise.) Historically, the midnight culmination of the Pleiades was very significant to many ancient and primitive peoples. Some of these Pleiades midnight celebrations still linger into the present, such as the old Druid rite of Halloween. Although the midnight culmination date for the Pleiades advances over the long course of time, the date of Halloween has remained fixed by tradition.

Tom Wildoner of LeisurelyScientist.com captured this image of the Pleiades on October 31, 2016.

Bottom line: Watch for the sky’s most celebrated star cluster – the Pleiades – a tiny, misty dipper-shaped star cluster adorning the sky all night long on these November nights.

More about the Pleiades: Famous Seven Sisters

from EarthSky https://ift.tt/2TwTkKW

Image at top: A laser pointer aims up past the V-shaped face of Taurus the Bull, toward the tiny, misty dipper of the Pleiades. Photo by Krishnan Subramanian near Mumbai, India.

Tonight, look for the tiny, misty dipper of stars known as the Pleiades or Seven Sisters. November is the month of the Pleiades star cluster. On these November nights, the Pleiades cluster shines from nightfall until dawn. It’s low in the east at nightfall, high overhead around midnight and low in the west before dawn. Locate it by the bright star Aldebaran this evening, or any evening soon.

The 2020 lunar calendars are here! Order yours before they’re gone. Makes a great gift.

You can view the Pleiades with either the unaided eye or an optical aid on these November nights. The Pleiades cluster is one of the most recognizable star patterns in the night sky. Its six brightest stars do look like a little dipper. In fact, people in the Northern Hemisphere often mistake the Pleiades for the real Little Dipper asterism, which is located farther north on the sky’s dome. The misty-looking dipper of the Pleiades hovers over the northeastern horizon as darkness falls. It moves across the night sky from east to west, much like the sun does during the day.

Do you love stargazing? Order an EarthSky planisphere

EarthSky community member Greg Hogan captured this image of the Pleiades in November 2015.

By the way, another name for the Pleiades is the Seven Sisters. But if you look with your eye alone, it’s likely you’ll only see six stars in the Pleiades. Some old Greek legends explore what might have happened to the missing sister, sometimes called the Lost Pleiad.

In the Northern Hemisphere, the Pleiades’ all-night appearance coincides with late autumn. As this part of the world moves toward winter, it’s easy to imagine the Pleiades as a frosty patch on the dome of night. But in the Southern Hemisphere now, where spring flowers are blooming, this cluster of nocturnal suns watches over the season of awakening and agriculture. In South Africa, for example, the Pleiades are called the hoeing-stars.

Yearly, on or near November 21, the Pleiades cluster culminates – reaches its highest point in the sky – at midnight. (In this instance, midnight means midway between sunset and sunrise.) Historically, the midnight culmination of the Pleiades was very significant to many ancient and primitive peoples. Some of these Pleiades midnight celebrations still linger into the present, such as the old Druid rite of Halloween. Although the midnight culmination date for the Pleiades advances over the long course of time, the date of Halloween has remained fixed by tradition.

Tom Wildoner of LeisurelyScientist.com captured this image of the Pleiades on October 31, 2016.

Bottom line: Watch for the sky’s most celebrated star cluster – the Pleiades – a tiny, misty dipper-shaped star cluster adorning the sky all night long on these November nights.

More about the Pleiades: Famous Seven Sisters

from EarthSky https://ift.tt/2TwTkKW

Moon and Leo from midnight until dawn

By the morning of November 19, 2019, we’ll be just one day past the peak of the Leonid meteor shower. The 2019 peak was mostly drowned in bright moonlight, and – if you look outside before dawn in the next few days – you’ll see the moon is moving directly in front of the Leonids’ radiant point, in the constellation Leo the Lion. You likely won’t see the moon and Regulus, Leo’s brightest star, before your bedtime Monday night. Watch for them before dawn this week. The moon and constellation Leo will be highest up for the night at or near dawn.

On the morning of November 19, the moon will be at or near its last quarter phase, and the lighted portion of the moon will be pointing toward Regulus. In a day or two, depending on where you live worldwide, the moon will pass Regulus, and then its lighted side will point away from Regulus and toward Spica, the constellation Virgo’s brightest star, as shown on the sky chart below. Spica should be pretty easy to see on these mornings because it rises before dawn’s first light.

This chart shows a greater expanse of sky than most of our sky charts do. The lit side of the moon points in the direction of Spica, the constellation Virgo’s brightest star, and the planets Mars and Mercury.

Once you find Spica, see if you spot the planets Mars and Mercury lurking beneath Spica with either the eye alone or binoculars. Mars is about half as bright as Spica, whereas Mercury is actually a bit brighter than Spica. But Mercury doesn’t rise until after the break of dawn, so it may be hard to spot this world in the glow of morning twilight on November 19 and 20. Day by day, however, Mercury will not only rise earlier before sunrise but will brighten as well, so Mercury may be yours to behold some morning soon.

The green line on our sky charts represents the ecliptic – Earth’s orbital plane projected onto the constellations of the zodiac. Because the planets orbit the sun, and the moon orbits Earth, on nearly the same plane that Earth circles the sun, the moon and planets are always found on or near the ecliptic. If you’re an early bird, waking up before the sun, then use the moon, the star Regulus and the star Spica to help you envision the ecliptic with the mind’s eye, and to find Mars and Mercury.

If you’re an early bird, waking up before the sun, then use the moon, the star Regulus and the star Spica to help you envision the ecliptic with the mind’s eye, and to find Mars and Mercury. Read more.

Regulus is the only first-magnitude star to sit almost squarely on the ecliptic, which – as alluded to before – marks the annual path of the sun, and approximate monthly path of the moon. The orbital planes of all the solar system planets pretty much align with the ecliptic.

In our day and age, the sun’s yearly conjunction with Regulus happens on or near August 23. That’s about two months after the June solstice, or about a month before the September equinox.

Early astronomers thought the sun literally moved through the constellations of the zodiac, while the Earth remained at rest at the center of the universe. Of course, we now know that the Earth revolves around the sun, and that the sun resides at the center of our solar system.

We also know that the sun’s apparent daily motion in front of the backdrop stars is really a reflection of Earth’s movement in orbit around the sun.

When you see Regulus near the moon on the mornings of November 19 and 20, 2019, remember … it’s a much larger star than our sun. Image via The Night Sky Guy.

Bottom line: See the waning gibbous moon near Regulus from around midnight until dawn. Then watch over the coming mornings as the moon moves past Regulus and toward the star Spica plus the planets Mars and Mercury.

EarthSky lunar calendars are cool! They make great gifts. Order now. Going fast!

Donate: Your support means the world to us

from EarthSky https://ift.tt/2psKEuD

By the morning of November 19, 2019, we’ll be just one day past the peak of the Leonid meteor shower. The 2019 peak was mostly drowned in bright moonlight, and – if you look outside before dawn in the next few days – you’ll see the moon is moving directly in front of the Leonids’ radiant point, in the constellation Leo the Lion. You likely won’t see the moon and Regulus, Leo’s brightest star, before your bedtime Monday night. Watch for them before dawn this week. The moon and constellation Leo will be highest up for the night at or near dawn.

On the morning of November 19, the moon will be at or near its last quarter phase, and the lighted portion of the moon will be pointing toward Regulus. In a day or two, depending on where you live worldwide, the moon will pass Regulus, and then its lighted side will point away from Regulus and toward Spica, the constellation Virgo’s brightest star, as shown on the sky chart below. Spica should be pretty easy to see on these mornings because it rises before dawn’s first light.

This chart shows a greater expanse of sky than most of our sky charts do. The lit side of the moon points in the direction of Spica, the constellation Virgo’s brightest star, and the planets Mars and Mercury.

Once you find Spica, see if you spot the planets Mars and Mercury lurking beneath Spica with either the eye alone or binoculars. Mars is about half as bright as Spica, whereas Mercury is actually a bit brighter than Spica. But Mercury doesn’t rise until after the break of dawn, so it may be hard to spot this world in the glow of morning twilight on November 19 and 20. Day by day, however, Mercury will not only rise earlier before sunrise but will brighten as well, so Mercury may be yours to behold some morning soon.

The green line on our sky charts represents the ecliptic – Earth’s orbital plane projected onto the constellations of the zodiac. Because the planets orbit the sun, and the moon orbits Earth, on nearly the same plane that Earth circles the sun, the moon and planets are always found on or near the ecliptic. If you’re an early bird, waking up before the sun, then use the moon, the star Regulus and the star Spica to help you envision the ecliptic with the mind’s eye, and to find Mars and Mercury.

If you’re an early bird, waking up before the sun, then use the moon, the star Regulus and the star Spica to help you envision the ecliptic with the mind’s eye, and to find Mars and Mercury. Read more.

Regulus is the only first-magnitude star to sit almost squarely on the ecliptic, which – as alluded to before – marks the annual path of the sun, and approximate monthly path of the moon. The orbital planes of all the solar system planets pretty much align with the ecliptic.

In our day and age, the sun’s yearly conjunction with Regulus happens on or near August 23. That’s about two months after the June solstice, or about a month before the September equinox.

Early astronomers thought the sun literally moved through the constellations of the zodiac, while the Earth remained at rest at the center of the universe. Of course, we now know that the Earth revolves around the sun, and that the sun resides at the center of our solar system.

We also know that the sun’s apparent daily motion in front of the backdrop stars is really a reflection of Earth’s movement in orbit around the sun.

When you see Regulus near the moon on the mornings of November 19 and 20, 2019, remember … it’s a much larger star than our sun. Image via The Night Sky Guy.

Bottom line: See the waning gibbous moon near Regulus from around midnight until dawn. Then watch over the coming mornings as the moon moves past Regulus and toward the star Spica plus the planets Mars and Mercury.

EarthSky lunar calendars are cool! They make great gifts. Order now. Going fast!

Donate: Your support means the world to us

from EarthSky https://ift.tt/2psKEuD

Curiosity’s ‘mind-boggling’ new Mars mystery: oxygen

Recent self-portrait of NASA’s Curiosity on Mars, stitched together from 57 individual images taken by a camera on the end of Curiosity’s robotic arm on October 11, 2019 (Sol 2,553). Image via NASA/JPL-Caltech/MSSS. Curious about Curiosity’s self-portraits? Here’s the story behind them.

The presence of methane in Mars’ atmosphere has been a fascinating puzzle for planetary scientists. That’s because, on Earth, methane is linked to life, but it can also be produced geologically. Some of the best data about Mars’ methane has come from the Curiosity rover, which landed on Mars after a daring descent through the atmosphere in August, 2012. Now Curiosity has made another intriguing discovery: oxygen at the rover’s location is behaving in ways that haven’t yet been explained by any known atmospheric or chemical process. The levels of the gas increase much more in the spring and summer months than had been predicted, similar to the still-mysterious methane. The big question, of course, is why?

The baffling peer-reviewed results were just published in the November 12, 2019, issue of the Journal of Geophysical Research: Planets.

Sushil Atreya, professor of climate and space sciences at the University of Michigan, said:

The first time we saw that, it was just mind boggling.

So just what is happening?

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Seasonal variations in oxygen levels in Gale Crater from 2012-2017. So far, scientists haven’t been able to explain these changes. Image via Melissa Trainer/Dan Gallagher/NASA Goddard/NASA.

Curiosity analyzed the composition of the air at Gale Crater over three Mars years (about six Earth years), using its Sample Analysis at Mars (SAM) portable chemistry lab. The results were pretty much what had been expected, and known for years: 95% carbon dioxide (CO2), 2.6% molecular nitrogen (N2), 1.9% argon (Ar), 0.16% molecular oxygen (O2), and 0.06% carbon monoxide (CO). (The methane is normally in much smaller amounts, about 0.00000004% on average).

The nitrogen and argon tend to follow a predictable pattern each year, increasing and decreasing relative to how much carbon dioxide there is. This is related to changing air pressure during the year, since carbon dioxide freezes as snow and ice over the planet’s poles during the winter, which lowers the air pressure. The air pressure rises again when the carbon dioxide evaporates in the spring and summer.

This is where it gets weird. Scientists had expected that the oxygen would follow the same pattern as the nitrogen and argon, but it didn’t. The oxygen level increased much more in spring and summer – as much as 30% – and then dropped back to normal levels, and even below, in the fall. This same process was observed by Curiosity each Martian spring and summer.

So what are the possible explanations? The researchers have considered several possibilities, but none of them explain all of the results.

Was there a problem with the SAM lab? The researchers checked but the instrument was fine and working properly.

Could carbon dioxide or water molecules have released oxygen when they broke apart in the atmosphere due to solar radiation? Probably not, since it would take five times more water vapor than exists to produce the amount of oxygen observed. Carbon dioxide would break up too slowly to generate the same amount of oxygen over such a short time period.

As for the oxygen decrease seen later, could that have been caused by solar radiation breaking apart oxygen molecules? No, since that would be an even slower process, taking up to 10 years.

The scientists involved also think it is unlikely to be caused simply by atmospheric circulation patterns. According to Melissa Trainer, a planetary scientist at NASA’s Goddard Space Flight Center (GFSC) who led the research:

We’re struggling to explain this. The fact that the oxygen behavior isn’t perfectly repeatable every season makes us think that it’s not an issue that has to do with atmospheric dynamics. It has to be some chemical source and sink that we can’t yet account for.

As Timothy McConnochie, assistant research scientist at the University of Maryland, also noted:

We have not been able to come up with one process yet that produces the amount of oxygen we need, but we think it has to be something in the surface soil that changes seasonally because there aren’t enough available oxygen atoms in the atmosphere to create the behavior we see.

Diagram showing the seasonal cycle of methane as detected by the Curiosity rover in Gale Crater. The methane also varies in concentration on a daily basis as well as seasonal. Image via NASA/JPL-Caltech/Mars Exploration Program.

The paper itself goes into more detail about each of these hypotheses and how none of them adequately explain the results so far. Yet something is producing a lot more oxygen during the warmer months than there should be. Intriguingly, both the oxygen and methane have been observed to fluctuate like this in tandem on at least some occasions, suggesting there may be a common source. As Atreya also noted:

We’re beginning to see this tantalizing correlation between methane and oxygen for a good part of the Mars year. I think there’s something to it. I just don’t have the answers yet. Nobody does.

On Earth, having oxygen and methane together is regarded as a biosignature, since they tend to destroy each other unless they are being continuously produced and fluxed into the atmosphere at relatively high rates. Because of this, the two gases are said to be in a state of thermodynamic disequilibrium.

By far, most of the oxygen and methane on Earth are produced by and/or consumed by life. Could that really be what’s happening on Mars? Or is there still some other unknown chemistry occurring? The Curiosity data showed that the background methane levels decreased at the same time as the oxygen levels did in the last half of each year, although the oxygen increases again earlier in the year than the methane, and is more variable year-to year. The larger “spike” in methane seen by Curiosity however, also occurred during the same period of time as the increase of oxygen in the spring. What all this means isn’t clear yet, and more study will be needed.

Melissa Trainer at Goddard Spaceflight Center (GFSC), who led the new research. Image via NASA/GFSC.

If there really is a correlation between the oxygen and methane on Mars, that could be a potential biosignature. A previous study in 2014 by Shawn Domagal-Goldman of NASA’s Goddard Space Flight Center found that while oxygen and methane by themselves could sometimes be created by non-biological processes, on exoplanets for example, but finding them together would be a more convincing biosignature:

However, our research strengthens the argument that methane and oxygen together, or methane and ozone together, are still strong signatures of life. We tried really, really hard to make false-positive signals for life, and we did find some, but only for oxygen, ozone, or methane by themselves.

These odd fluctuations in the oxygen levels at Gale Crater – with a possible connection to the methane fluctuations and spikes – are a fascinating new mystery for Mars scientists to try and solve. As Trainer summarized:

This is the first time where we’re seeing this interesting behavior over multiple years. We don’t totally understand it. For me, this is an open call to all the smart people out there who are interested in this: See what you can come up with.

Bottom line: NASA’s Curiosity rover has detected unusual increases and decreases in the level of oxygen in the air at Gale Crater. In some ways these are similar to the fluctuations of methane, and may even be connected.

Source: Seasonal variations in atmospheric composition as measured in Gale Crater, Mars

Via NASA

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Recent self-portrait of NASA’s Curiosity on Mars, stitched together from 57 individual images taken by a camera on the end of Curiosity’s robotic arm on October 11, 2019 (Sol 2,553). Image via NASA/JPL-Caltech/MSSS. Curious about Curiosity’s self-portraits? Here’s the story behind them.

The presence of methane in Mars’ atmosphere has been a fascinating puzzle for planetary scientists. That’s because, on Earth, methane is linked to life, but it can also be produced geologically. Some of the best data about Mars’ methane has come from the Curiosity rover, which landed on Mars after a daring descent through the atmosphere in August, 2012. Now Curiosity has made another intriguing discovery: oxygen at the rover’s location is behaving in ways that haven’t yet been explained by any known atmospheric or chemical process. The levels of the gas increase much more in the spring and summer months than had been predicted, similar to the still-mysterious methane. The big question, of course, is why?

The baffling peer-reviewed results were just published in the November 12, 2019, issue of the Journal of Geophysical Research: Planets.

Sushil Atreya, professor of climate and space sciences at the University of Michigan, said:

The first time we saw that, it was just mind boggling.

So just what is happening?

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Seasonal variations in oxygen levels in Gale Crater from 2012-2017. So far, scientists haven’t been able to explain these changes. Image via Melissa Trainer/Dan Gallagher/NASA Goddard/NASA.

Curiosity analyzed the composition of the air at Gale Crater over three Mars years (about six Earth years), using its Sample Analysis at Mars (SAM) portable chemistry lab. The results were pretty much what had been expected, and known for years: 95% carbon dioxide (CO2), 2.6% molecular nitrogen (N2), 1.9% argon (Ar), 0.16% molecular oxygen (O2), and 0.06% carbon monoxide (CO). (The methane is normally in much smaller amounts, about 0.00000004% on average).

The nitrogen and argon tend to follow a predictable pattern each year, increasing and decreasing relative to how much carbon dioxide there is. This is related to changing air pressure during the year, since carbon dioxide freezes as snow and ice over the planet’s poles during the winter, which lowers the air pressure. The air pressure rises again when the carbon dioxide evaporates in the spring and summer.

This is where it gets weird. Scientists had expected that the oxygen would follow the same pattern as the nitrogen and argon, but it didn’t. The oxygen level increased much more in spring and summer – as much as 30% – and then dropped back to normal levels, and even below, in the fall. This same process was observed by Curiosity each Martian spring and summer.

So what are the possible explanations? The researchers have considered several possibilities, but none of them explain all of the results.

Was there a problem with the SAM lab? The researchers checked but the instrument was fine and working properly.

Could carbon dioxide or water molecules have released oxygen when they broke apart in the atmosphere due to solar radiation? Probably not, since it would take five times more water vapor than exists to produce the amount of oxygen observed. Carbon dioxide would break up too slowly to generate the same amount of oxygen over such a short time period.

As for the oxygen decrease seen later, could that have been caused by solar radiation breaking apart oxygen molecules? No, since that would be an even slower process, taking up to 10 years.

The scientists involved also think it is unlikely to be caused simply by atmospheric circulation patterns. According to Melissa Trainer, a planetary scientist at NASA’s Goddard Space Flight Center (GFSC) who led the research:

We’re struggling to explain this. The fact that the oxygen behavior isn’t perfectly repeatable every season makes us think that it’s not an issue that has to do with atmospheric dynamics. It has to be some chemical source and sink that we can’t yet account for.

As Timothy McConnochie, assistant research scientist at the University of Maryland, also noted:

We have not been able to come up with one process yet that produces the amount of oxygen we need, but we think it has to be something in the surface soil that changes seasonally because there aren’t enough available oxygen atoms in the atmosphere to create the behavior we see.

Diagram showing the seasonal cycle of methane as detected by the Curiosity rover in Gale Crater. The methane also varies in concentration on a daily basis as well as seasonal. Image via NASA/JPL-Caltech/Mars Exploration Program.

The paper itself goes into more detail about each of these hypotheses and how none of them adequately explain the results so far. Yet something is producing a lot more oxygen during the warmer months than there should be. Intriguingly, both the oxygen and methane have been observed to fluctuate like this in tandem on at least some occasions, suggesting there may be a common source. As Atreya also noted:

We’re beginning to see this tantalizing correlation between methane and oxygen for a good part of the Mars year. I think there’s something to it. I just don’t have the answers yet. Nobody does.

On Earth, having oxygen and methane together is regarded as a biosignature, since they tend to destroy each other unless they are being continuously produced and fluxed into the atmosphere at relatively high rates. Because of this, the two gases are said to be in a state of thermodynamic disequilibrium.

By far, most of the oxygen and methane on Earth are produced by and/or consumed by life. Could that really be what’s happening on Mars? Or is there still some other unknown chemistry occurring? The Curiosity data showed that the background methane levels decreased at the same time as the oxygen levels did in the last half of each year, although the oxygen increases again earlier in the year than the methane, and is more variable year-to year. The larger “spike” in methane seen by Curiosity however, also occurred during the same period of time as the increase of oxygen in the spring. What all this means isn’t clear yet, and more study will be needed.

Melissa Trainer at Goddard Spaceflight Center (GFSC), who led the new research. Image via NASA/GFSC.

If there really is a correlation between the oxygen and methane on Mars, that could be a potential biosignature. A previous study in 2014 by Shawn Domagal-Goldman of NASA’s Goddard Space Flight Center found that while oxygen and methane by themselves could sometimes be created by non-biological processes, on exoplanets for example, but finding them together would be a more convincing biosignature:

However, our research strengthens the argument that methane and oxygen together, or methane and ozone together, are still strong signatures of life. We tried really, really hard to make false-positive signals for life, and we did find some, but only for oxygen, ozone, or methane by themselves.

These odd fluctuations in the oxygen levels at Gale Crater – with a possible connection to the methane fluctuations and spikes – are a fascinating new mystery for Mars scientists to try and solve. As Trainer summarized:

This is the first time where we’re seeing this interesting behavior over multiple years. We don’t totally understand it. For me, this is an open call to all the smart people out there who are interested in this: See what you can come up with.

Bottom line: NASA’s Curiosity rover has detected unusual increases and decreases in the level of oxygen in the air at Gale Crater. In some ways these are similar to the fluctuations of methane, and may even be connected.

Source: Seasonal variations in atmospheric composition as measured in Gale Crater, Mars

Via NASA

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Black hole hurls star out of Milky Way

Artist’s concept of the Milky Way’s central, giant black hole flinging a star from our galaxy’s center. Image via James Josephides (Swinburne Astronomy Productions).

A new study by an international team of astronomers has discovered a star traveling at about 4 million miles (more than 6 million km) per hour through the Milky Way. The scientists say the star – named S5-HVs1 – was flung from the center of our galaxy by a supermassive black hole about 5 million years ago, around the time our ancestors here on Earth were just learning to walk upright.

The star, about 29,000 light-years away, is moving so fast that it will leave the Milky Way in about 100 million years, never to return, said Gary Da Costa, an astronomer at Australian National University (ANU). He is lead author of the study, published November 4, 2019, in the peer-reviewed Monthly Notices of the Royal Astronomical Society, and said in a statement:

This star is traveling at record-breaking speed – 10 times faster than most stars in the Milky Way, including our sun.

In astronomical terms, the star will be leaving our galaxy fairly soon, and it’ll likely travel through the emptiness of intergalactic space for eternity. It’s great to be able to confirm a 30-year-old prediction that stars can be flung out of a galaxy by the supermassive black hole at its center.

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An illustration by the Royal Astronomical Society of the location of the hyper-fast star and the direction of its motion. Image via Sergey Koposov/PA/The Guardian.

The giant black hole at the center of the Milky Way, Sagittarius A*, has a mass equivalent to more than four million suns. Study co-author Thomas Nordlander, of Australian National University, said supermassive black holes can slingshot stars by interacting with a binary stellar system, where two stars orbit around each other. He said:

If such a binary system approaches a black hole too closely, the black hole can capture one of the stars into a close orbit and kick out the other at very high speed.

The team spotted the fast-moving star serendipitously while using the Anglo-Australian Telescope at the ANU Siding Spring Observatory to search for the shredded remains of small galaxies orbiting the Milky Way.

Bottom line: Astronomers have spotted a star – S5-HVs1 – speeding out of the Milky Way at around 4 million miles (more than 6 million km) per hour. They believe it’s being ejected from our galaxy after venturing too near the giant black hole at the Milky Way’s heart about 5 million years ago.

Source: Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*

Via Australian National University

from EarthSky https://ift.tt/35glPl5

Artist’s concept of the Milky Way’s central, giant black hole flinging a star from our galaxy’s center. Image via James Josephides (Swinburne Astronomy Productions).

A new study by an international team of astronomers has discovered a star traveling at about 4 million miles (more than 6 million km) per hour through the Milky Way. The scientists say the star – named S5-HVs1 – was flung from the center of our galaxy by a supermassive black hole about 5 million years ago, around the time our ancestors here on Earth were just learning to walk upright.

The star, about 29,000 light-years away, is moving so fast that it will leave the Milky Way in about 100 million years, never to return, said Gary Da Costa, an astronomer at Australian National University (ANU). He is lead author of the study, published November 4, 2019, in the peer-reviewed Monthly Notices of the Royal Astronomical Society, and said in a statement:

This star is traveling at record-breaking speed – 10 times faster than most stars in the Milky Way, including our sun.

In astronomical terms, the star will be leaving our galaxy fairly soon, and it’ll likely travel through the emptiness of intergalactic space for eternity. It’s great to be able to confirm a 30-year-old prediction that stars can be flung out of a galaxy by the supermassive black hole at its center.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

An illustration by the Royal Astronomical Society of the location of the hyper-fast star and the direction of its motion. Image via Sergey Koposov/PA/The Guardian.

The giant black hole at the center of the Milky Way, Sagittarius A*, has a mass equivalent to more than four million suns. Study co-author Thomas Nordlander, of Australian National University, said supermassive black holes can slingshot stars by interacting with a binary stellar system, where two stars orbit around each other. He said:

If such a binary system approaches a black hole too closely, the black hole can capture one of the stars into a close orbit and kick out the other at very high speed.

The team spotted the fast-moving star serendipitously while using the Anglo-Australian Telescope at the ANU Siding Spring Observatory to search for the shredded remains of small galaxies orbiting the Milky Way.

Bottom line: Astronomers have spotted a star – S5-HVs1 – speeding out of the Milky Way at around 4 million miles (more than 6 million km) per hour. They believe it’s being ejected from our galaxy after venturing too near the giant black hole at the Milky Way’s heart about 5 million years ago.

Source: Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*

Via Australian National University

from EarthSky https://ift.tt/35glPl5

Composite image of SpaceX Starlink satellite swarm

EarthSky friend Padraic Koen was in Arkaroola, South Australia this morning, when a swarm of 25 SpaceX StarLink satellites passed over between 4:51 and 5:01 a.m. He created this composite of three 15-second shots – taken a few minutes apart – that captured 14 of the satellites. Thank you, Padraic!

Last week – on Monday, November 11, 2019 – a SpaceX Falcon 9 rocket launched 60 more Starlink satellites to Earth-orbit. According to Stephen Clark at SpaceFlightNow.com, the satellites traced paths across twilight skies around the world last week, and, even this morning (November 18) astrophotographers are still capturing them, as shown in this image from our friend Padraic Koen.

How long will we be able to see this batch of Starlink satellites? No one is exactly sure, but, even now, you’ll certainly need a dark sky. Clark explained:

… their brightness is expected to dim as the spacecraft — designed to beam broadband signals down to Earth — spread out and climb to higher altitudes.

The satellite-tracking website Heavens-Above.com updated its Starlink satellite page most recently on November 14. Go to its dynamic display of all objects from the recent Starlink launch.

SpaceX plans to launch thousands of Starlink satellites in the coming years, including hundreds more in 2020. The project will eventually place an initial 12,000 satellites in low-Earth orbit to provide worldwide internet access. Each satellite is the size of a table and includes a reflective solar panel for power.

Read more from SpaceFlightNow: Starlink ‘train’ traces path across twilight skies

Read more from SkyandTelescope.com: SpaceX launches latest batch of Starlink satellites

Bottom line: Composite of three 15-second photos – taken a few minutes apart – capturing 14 of the recently launched SpaceX Starlink satellites.

from EarthSky https://ift.tt/2Kwla73

EarthSky friend Padraic Koen was in Arkaroola, South Australia this morning, when a swarm of 25 SpaceX StarLink satellites passed over between 4:51 and 5:01 a.m. He created this composite of three 15-second shots – taken a few minutes apart – that captured 14 of the satellites. Thank you, Padraic!

Last week – on Monday, November 11, 2019 – a SpaceX Falcon 9 rocket launched 60 more Starlink satellites to Earth-orbit. According to Stephen Clark at SpaceFlightNow.com, the satellites traced paths across twilight skies around the world last week, and, even this morning (November 18) astrophotographers are still capturing them, as shown in this image from our friend Padraic Koen.

How long will we be able to see this batch of Starlink satellites? No one is exactly sure, but, even now, you’ll certainly need a dark sky. Clark explained:

… their brightness is expected to dim as the spacecraft — designed to beam broadband signals down to Earth — spread out and climb to higher altitudes.

The satellite-tracking website Heavens-Above.com updated its Starlink satellite page most recently on November 14. Go to its dynamic display of all objects from the recent Starlink launch.

SpaceX plans to launch thousands of Starlink satellites in the coming years, including hundreds more in 2020. The project will eventually place an initial 12,000 satellites in low-Earth orbit to provide worldwide internet access. Each satellite is the size of a table and includes a reflective solar panel for power.

Read more from SpaceFlightNow: Starlink ‘train’ traces path across twilight skies

Read more from SkyandTelescope.com: SpaceX launches latest batch of Starlink satellites

Bottom line: Composite of three 15-second photos – taken a few minutes apart – capturing 14 of the recently launched SpaceX Starlink satellites.

from EarthSky https://ift.tt/2Kwla73