When astronomers speak of solar noon, they aren’t speaking of clock time. But clock noon and your solar noon do sometimes coincide. Solar noon is when the sun reaches its highest point in your sky for the day. Astronomer Guy Ottewell explains the equation of time, below. Image via EarthSky.
The length of our day is 24 hours. You could look at day length as the average time between local noons, when the sun reaches its highest point in your sky. If you time those crossings with a stopwatch, you will find that the sun sometimes reaches the meridian – a line across your sky from due north to due south, dividing your sky in half – slightly early. And it sometimes crosses the meridian slightly late. So, the observed, or apparent, lengths of the day vary.
This is partly because the Earth travels slightly faster during the inner half of its slightly elliptical orbit around the sun. That’s when we’re near perihelion – its closest point to the sun in its orbit around January 3 – than in the outer half (aphelion). However, Earth rotates at a constant speed.
From perihelion (early January) onward a spot that is on the Earth begins arriving slightly later each day at the direction facing the sun, because Earth is slowing in its orbit. (Exaggerated in this diagram.) Image via Guy Ottewell. Used with permission.
Earth’s tilt is a major factor
But the larger reason is Earth’s obliquity: the tilting of its north pole 23.4° away from the sun around the December solstices and toward it around the June solstices. Around the times of the December and June solstices (from early November to early February, and from early May to early August), the sun travels across the lines of right ascension on the map of the sky faster than it is traveling in longitude.
Then around the March equinox (from early February to early May), its course slopes north in right ascension. And around the September equinox (from early August to early November) it slopes south, so at those times the sun’s right ascension changes more slowly than its longitude.
Another way of putting it is that, as the sun moves one day’s journey along the ecliptic, it moves more or less than that angular distance in right ascension, which is the measure of when it’s on the meridian at noon.
The difference between apparent solar time (the actual time between noons) and mean solar time (the average time between noons) is called the equation of time. This old use of equation means that by subtracting it from the varying apparent time you equalize that to the average time.
The results: Minima and maxima
The two factors above combine to give a curve showing two minima and two maxima.
The dates can vary slightly from year to year because of leap days. These are the dates for 2020:
February 11 is at minimum for the year -14.24 minutes.
April 15 is 0.
May 13 reaches a shallow maximum of 3.65 minutes.
June 12 is 0.
July 25 reaches a shallow minimum of -6.55 minutes.
September 1 is 0.
November 2 is at maximum for the year, 16.49 minutes.
December 24 is 0.
In February, the equation reaches its deepest minimum, about 14 minutes. Although it’s 12 noon by clock time, the sun is 14 minutes short of reaching the meridian. So the sun is slow, or clocks are fast (this shouldn’t be confused with the speed of Earth in its orbit). Image via Guy Ottewell. Used with permission.
Then, there comes a small maximum in May (at mean noon the sun is 4 minutes past the meridian). Next, it’s followed by a smaller minimum in July (the sun is 7 minutes late reaching the meridian). And a year’s maximum is in November (the sun is 16.5 minutes early crossing the meridian). Finally, the dates in between – April, June, September, December – are when the equation is zero. So the midday sun is on time!
Now factoring in axial tilt and eccentricity
Here is the graph with the addition of curves for the 2 components: obliquity (red) and eccentricity (green). Image via Guy Ottewell. Used with permission.
These are the words of friend Anthony Barreiro. He suggested the addition of the curves for the two components, and I can’t improve on his explanation.
You can see why the February minimum and November maximum are extreme, while the May maximum and July minimum are moderate, and also how the equation of time is mostly due to obliquity (axial tilt), with eccentricity pulling it first one way then the other.
Bottom line: Guy Ottewell discusses the difference between apparent solar time (the actual time between noons) and mean solar time (the average time between noons). It’s called the equation of time.
When astronomers speak of solar noon, they aren’t speaking of clock time. But clock noon and your solar noon do sometimes coincide. Solar noon is when the sun reaches its highest point in your sky for the day. Astronomer Guy Ottewell explains the equation of time, below. Image via EarthSky.
The length of our day is 24 hours. You could look at day length as the average time between local noons, when the sun reaches its highest point in your sky. If you time those crossings with a stopwatch, you will find that the sun sometimes reaches the meridian – a line across your sky from due north to due south, dividing your sky in half – slightly early. And it sometimes crosses the meridian slightly late. So, the observed, or apparent, lengths of the day vary.
This is partly because the Earth travels slightly faster during the inner half of its slightly elliptical orbit around the sun. That’s when we’re near perihelion – its closest point to the sun in its orbit around January 3 – than in the outer half (aphelion). However, Earth rotates at a constant speed.
From perihelion (early January) onward a spot that is on the Earth begins arriving slightly later each day at the direction facing the sun, because Earth is slowing in its orbit. (Exaggerated in this diagram.) Image via Guy Ottewell. Used with permission.
Earth’s tilt is a major factor
But the larger reason is Earth’s obliquity: the tilting of its north pole 23.4° away from the sun around the December solstices and toward it around the June solstices. Around the times of the December and June solstices (from early November to early February, and from early May to early August), the sun travels across the lines of right ascension on the map of the sky faster than it is traveling in longitude.
Then around the March equinox (from early February to early May), its course slopes north in right ascension. And around the September equinox (from early August to early November) it slopes south, so at those times the sun’s right ascension changes more slowly than its longitude.
Another way of putting it is that, as the sun moves one day’s journey along the ecliptic, it moves more or less than that angular distance in right ascension, which is the measure of when it’s on the meridian at noon.
The difference between apparent solar time (the actual time between noons) and mean solar time (the average time between noons) is called the equation of time. This old use of equation means that by subtracting it from the varying apparent time you equalize that to the average time.
The results: Minima and maxima
The two factors above combine to give a curve showing two minima and two maxima.
The dates can vary slightly from year to year because of leap days. These are the dates for 2020:
February 11 is at minimum for the year -14.24 minutes.
April 15 is 0.
May 13 reaches a shallow maximum of 3.65 minutes.
June 12 is 0.
July 25 reaches a shallow minimum of -6.55 minutes.
September 1 is 0.
November 2 is at maximum for the year, 16.49 minutes.
December 24 is 0.
In February, the equation reaches its deepest minimum, about 14 minutes. Although it’s 12 noon by clock time, the sun is 14 minutes short of reaching the meridian. So the sun is slow, or clocks are fast (this shouldn’t be confused with the speed of Earth in its orbit). Image via Guy Ottewell. Used with permission.
Then, there comes a small maximum in May (at mean noon the sun is 4 minutes past the meridian). Next, it’s followed by a smaller minimum in July (the sun is 7 minutes late reaching the meridian). And a year’s maximum is in November (the sun is 16.5 minutes early crossing the meridian). Finally, the dates in between – April, June, September, December – are when the equation is zero. So the midday sun is on time!
Now factoring in axial tilt and eccentricity
Here is the graph with the addition of curves for the 2 components: obliquity (red) and eccentricity (green). Image via Guy Ottewell. Used with permission.
These are the words of friend Anthony Barreiro. He suggested the addition of the curves for the two components, and I can’t improve on his explanation.
You can see why the February minimum and November maximum are extreme, while the May maximum and July minimum are moderate, and also how the equation of time is mostly due to obliquity (axial tilt), with eccentricity pulling it first one way then the other.
Bottom line: Guy Ottewell discusses the difference between apparent solar time (the actual time between noons) and mean solar time (the average time between noons). It’s called the equation of time.
View larger. | Artist’s concept of the Beta Pictoris system, only 63 light-years from Earth. It’s a newly forming solar system. NASA’s Webb space telescope has found evidence for a giant asteroid collision within this system. Image via NASA/ Lynette Cook/ Johns Hopkins University.
The Beta Pictoris system is young, only about 20 million years old. It’s young enough to be in the process of forming planets. It has at least two gas giant planets and smaller rocky planets possibly starting to form as well.
Planets form from a swirling cloud of gas, dust, and rocky debris. In this cloud are many collisions, and collisions are part of the process that makes planets.
Astronomers now see evidence for a massive asteroid collision in the Beta Pictoris star system.
Asteroid collision in young star system
Asteroids are chunks of material remaining from the vast and violent process of collisions that took place in our early solar system. In our solar system, 4.5 billion years ago, planets are thought to have formed from a vast cloud in space surrounding our young sun. And the latter part of the planet-forming process involved collisions between asteroids. We know some of the larger young asteroids collided to form even-bigger ones. Could some asteroid collisions have led to bodies large enough to develop enough self-gravity to become round planets? Now we have a chance to study that possibility. A team of researchers, led by Johns Hopkins University, said on June 10, 2024, that they’ve found evidence for a giant asteroid collision in the Beta Pictoris star system, only 63 light-years away.
The Beta Pictoris system is fascinating to astronomers. It’s nearby and can provide evidence of theories of solar system formation that have been around since at least the mid-20th century. Beta Pictoris is seen by powerful telescopes to be surrounded by a disk of debris. At least two gas giant planets are known to be forming in this protoplanetary disk. Lead author Christine Chen, an astronomer at Johns Hopkins University, said:
Beta Pictoris is at an age when planet formation in the terrestrial planet zone [the zone where rocky planets form] is still ongoing through giant asteroid collisions. So what we could be seeing here is basically how rocky planets and other bodies are forming in real time.
The “real-time” aspect of this discovery is really exciting. In the reckoning of earthly astronomers, the giant asterid collision they observed happened only 20 years ago (that’s 20 years, plus the 63 years the light had to travel to reach our eyes). Real time indeed for any astronomical discovery, where timescales typically measure in the millions or billions of years.
Beta Pictoris is young
The Beta Pictoris system is much younger than our solar system. It’s about only 20 million years old. It’s like a baby compared with our solar system, which is 4.5 billion years old. And the giant asteroid collision – just observed – is thought to have taken place just 20 years ago (plus 63 years of light-travel time).
The abstract of the presentation is available here.
View larger. | Mid-infrared data of Beta Pictoris from Webb (2023) and Spitzer (2004-2005). Image via Roberto Molar Candanosa/ Johns Hopkins University/ Lynette Cook/ NASA.
Clues about how planetary systems evolve
Our solar system has two basic kinds of objects we call planets. Some are large gas giants such as Jupiter and Saturn. And some are smaller rocky worlds such as Earth and Mars. Beta Pictoris has two known gas giant planets, Beta Pictoris b and Beta Pictoris c. Beta Pictoris b was discovered in 2008 and Beta Pictoris c in 2020.
Remember that the star Beta Pictoris is only 20 million years old. So these big planets, Beta Pictoris b and c, are not unexpected. These big gas worlds would be expected to form first in a fledgling solar system.
Meanwhile, at just 20 million years, any rocky planets would likely still be in the process of forming. And asteroid collisions should be part of this process. This makes Beta Pictoris an ideal system to study for clues about how planetary systems evolve in general, and about how rocky worlds, such as our own Earth, might have come to be. Being relatively close by at 63 light-years helps, too. It means astronomers can study the random processes involved, such as asteroid collisions and space weathering. Co-author Kadin Worthen, a doctoral student in astrophysics at Johns Hopkins University, said:
The question we are trying to contextualize is whether this whole process of terrestrial and giant planet formation is common or rare, and the even more basic question: Are planetary systems like the solar system that rare? We’re basically trying to understand how weird or average we are.
Data from Webb and Spitzer
The researchers made the discovery by combining new data from Webb and old data from Spitzer from 2004 and 2005. Spitzer had previously identified dust particles around the young star. Subsequently, Webb tracked the composition and size of particles in the same region. Webb’s observations, however, revealed significant energy changes in the particles.
This meant that these weren’t the same particles – crystalline silicates – that Spitzer saw. But why? The researchers said that there were collisions among asteroids as recently as 20 years ago. The newer particles are now much smaller, smaller than pollen or powdered sugar. Those collisions created all the new dust. Chen explained:
We think all that dust is what we saw initially in the Spitzer data from 2004 and 2005. With Webb’s new data, the best explanation we have is that, in fact, we witnessed the aftermath of an infrequent, cataclysmic event between large asteroid-size bodies, marking a complete change in our understanding of this star system.
The results also suggest that dust originally pushed outward from the star by radiation is no longer detectable. That dust, once heated by the radiation and making it easier to detect, has now cooled off. And contrary to previous assumptions, the dust was not replenished by later collisions. Instead, it just disappeared. The amount of dust from these collisions is about 100,000 times larger than the asteroid that hit Earth and wiped out the dinosaurs.
View larger. | Infrared image of Beta Pictoris, from the Very Large Telescope in 2008. The 1st of the 2 known gas giant planets, Beta Pictoris b, was seen here for the 1st time. Image via ESO/ A.-M. Lagrange et al.
For this discovery, it’s what Webb didn’t see
The researchers also noted that, in this case, the results came from what Webb didn’t see – the same original dust – instead of what it did. As co-author Cicero Lu, a former Johns Hopkins doctoral student in astrophysics, pointed out:
Most discoveries by JWST come from things the telescope has detected directly. In this case, the story is a little different because our results come from what JWST did not see.
Last February, scientists said that the Webb telescope found a massive “cat’s tail” of dust in the Beta Pictoris system, some 10 billion miles (16 billion km) long.
In 2022, astronomers also discovered 30 exocomets orbiting the star in the Beta Pictoris system. The sizes ranged from about 1.9 to 8.7 miles (3 to 14 km) in diameter. Data from TESS showed that the distribution of the comets is very similar to that of comets in our own solar system.
Bottom line: NASA’s Webb space telescope has found evidence of a giant asteroid collision that occurred in the Beta Pictoris star system only about 20 years ago.
View larger. | Artist’s concept of the Beta Pictoris system, only 63 light-years from Earth. It’s a newly forming solar system. NASA’s Webb space telescope has found evidence for a giant asteroid collision within this system. Image via NASA/ Lynette Cook/ Johns Hopkins University.
The Beta Pictoris system is young, only about 20 million years old. It’s young enough to be in the process of forming planets. It has at least two gas giant planets and smaller rocky planets possibly starting to form as well.
Planets form from a swirling cloud of gas, dust, and rocky debris. In this cloud are many collisions, and collisions are part of the process that makes planets.
Astronomers now see evidence for a massive asteroid collision in the Beta Pictoris star system.
Asteroid collision in young star system
Asteroids are chunks of material remaining from the vast and violent process of collisions that took place in our early solar system. In our solar system, 4.5 billion years ago, planets are thought to have formed from a vast cloud in space surrounding our young sun. And the latter part of the planet-forming process involved collisions between asteroids. We know some of the larger young asteroids collided to form even-bigger ones. Could some asteroid collisions have led to bodies large enough to develop enough self-gravity to become round planets? Now we have a chance to study that possibility. A team of researchers, led by Johns Hopkins University, said on June 10, 2024, that they’ve found evidence for a giant asteroid collision in the Beta Pictoris star system, only 63 light-years away.
The Beta Pictoris system is fascinating to astronomers. It’s nearby and can provide evidence of theories of solar system formation that have been around since at least the mid-20th century. Beta Pictoris is seen by powerful telescopes to be surrounded by a disk of debris. At least two gas giant planets are known to be forming in this protoplanetary disk. Lead author Christine Chen, an astronomer at Johns Hopkins University, said:
Beta Pictoris is at an age when planet formation in the terrestrial planet zone [the zone where rocky planets form] is still ongoing through giant asteroid collisions. So what we could be seeing here is basically how rocky planets and other bodies are forming in real time.
The “real-time” aspect of this discovery is really exciting. In the reckoning of earthly astronomers, the giant asterid collision they observed happened only 20 years ago (that’s 20 years, plus the 63 years the light had to travel to reach our eyes). Real time indeed for any astronomical discovery, where timescales typically measure in the millions or billions of years.
Beta Pictoris is young
The Beta Pictoris system is much younger than our solar system. It’s about only 20 million years old. It’s like a baby compared with our solar system, which is 4.5 billion years old. And the giant asteroid collision – just observed – is thought to have taken place just 20 years ago (plus 63 years of light-travel time).
The abstract of the presentation is available here.
View larger. | Mid-infrared data of Beta Pictoris from Webb (2023) and Spitzer (2004-2005). Image via Roberto Molar Candanosa/ Johns Hopkins University/ Lynette Cook/ NASA.
Clues about how planetary systems evolve
Our solar system has two basic kinds of objects we call planets. Some are large gas giants such as Jupiter and Saturn. And some are smaller rocky worlds such as Earth and Mars. Beta Pictoris has two known gas giant planets, Beta Pictoris b and Beta Pictoris c. Beta Pictoris b was discovered in 2008 and Beta Pictoris c in 2020.
Remember that the star Beta Pictoris is only 20 million years old. So these big planets, Beta Pictoris b and c, are not unexpected. These big gas worlds would be expected to form first in a fledgling solar system.
Meanwhile, at just 20 million years, any rocky planets would likely still be in the process of forming. And asteroid collisions should be part of this process. This makes Beta Pictoris an ideal system to study for clues about how planetary systems evolve in general, and about how rocky worlds, such as our own Earth, might have come to be. Being relatively close by at 63 light-years helps, too. It means astronomers can study the random processes involved, such as asteroid collisions and space weathering. Co-author Kadin Worthen, a doctoral student in astrophysics at Johns Hopkins University, said:
The question we are trying to contextualize is whether this whole process of terrestrial and giant planet formation is common or rare, and the even more basic question: Are planetary systems like the solar system that rare? We’re basically trying to understand how weird or average we are.
Data from Webb and Spitzer
The researchers made the discovery by combining new data from Webb and old data from Spitzer from 2004 and 2005. Spitzer had previously identified dust particles around the young star. Subsequently, Webb tracked the composition and size of particles in the same region. Webb’s observations, however, revealed significant energy changes in the particles.
This meant that these weren’t the same particles – crystalline silicates – that Spitzer saw. But why? The researchers said that there were collisions among asteroids as recently as 20 years ago. The newer particles are now much smaller, smaller than pollen or powdered sugar. Those collisions created all the new dust. Chen explained:
We think all that dust is what we saw initially in the Spitzer data from 2004 and 2005. With Webb’s new data, the best explanation we have is that, in fact, we witnessed the aftermath of an infrequent, cataclysmic event between large asteroid-size bodies, marking a complete change in our understanding of this star system.
The results also suggest that dust originally pushed outward from the star by radiation is no longer detectable. That dust, once heated by the radiation and making it easier to detect, has now cooled off. And contrary to previous assumptions, the dust was not replenished by later collisions. Instead, it just disappeared. The amount of dust from these collisions is about 100,000 times larger than the asteroid that hit Earth and wiped out the dinosaurs.
View larger. | Infrared image of Beta Pictoris, from the Very Large Telescope in 2008. The 1st of the 2 known gas giant planets, Beta Pictoris b, was seen here for the 1st time. Image via ESO/ A.-M. Lagrange et al.
For this discovery, it’s what Webb didn’t see
The researchers also noted that, in this case, the results came from what Webb didn’t see – the same original dust – instead of what it did. As co-author Cicero Lu, a former Johns Hopkins doctoral student in astrophysics, pointed out:
Most discoveries by JWST come from things the telescope has detected directly. In this case, the story is a little different because our results come from what JWST did not see.
Last February, scientists said that the Webb telescope found a massive “cat’s tail” of dust in the Beta Pictoris system, some 10 billion miles (16 billion km) long.
In 2022, astronomers also discovered 30 exocomets orbiting the star in the Beta Pictoris system. The sizes ranged from about 1.9 to 8.7 miles (3 to 14 km) in diameter. Data from TESS showed that the distribution of the comets is very similar to that of comets in our own solar system.
Bottom line: NASA’s Webb space telescope has found evidence of a giant asteroid collision that occurred in the Beta Pictoris star system only about 20 years ago.
Sea rays are flying-saucer-shaped fish with long tails that skim along the seafloor. Many people lump all sea rays together and call them stingrays, but not all sea rays sting. In fact, some don’t even have stingers. A stingray is just one type of sea ray. In total, there are some 600 species of sea ray!
Even without a stinger, rays can be dangerous. We couldn’t expect any less, considering they’re descendants of sharks. So, apart from having very strong teeth, some rays can sting, and some can even produce electric discharges.
Sea rays are descendants of sharks
Sea rays are closely related to sharks. Rays first appeared in the fossil record about 200 million years ago, about 200 million years after the first sharks. They are believed to have evolved from flattened shark species.
Both animals share the same general skeletal structure. But did you know neither sharks nor rays have bones? Instead they have cartilage, a light, flexible and strong connective tissue. This exceptional adaptation improves their maneuverability and resistance underwater.
Thus, the ray is a cartilaginous fish belonging to the Batoidea superorder. These animals are easy to recognize because they’re very flat and, in the vast majority of cases, have long, round fins to move quickly through the water, and long, thin tails.
Rays are cartilaginous fish that look very flat, have long, round fins and have a long, thin tail. Image via Enrique Ortega Miranda/ Unsplash.
A very peculiar anatomy
These animals have fins that surround their entire body. The pectoral fins form a large disc and begin at the back of the skull. These fins are always undulating because, if they didn’t, the animal would sink. The pelvic fins are quite small and are integrated behind the pectoral fins.
The tail can be short and robust or thin and elongated. However, most species have a fairly long and thin tail.
As they are fish, rays have gills to breathe. In fact, they have five pairs of gill slits in the lower part of their body.
In addition, at the top of their body, next to the eyes, are the so-called spiracles, which are often confused with the eyes. The spiracles help them breathe when they are half buried and camouflaged under the sand.
Rays have gills to breathe, but they also have spiracles next to the eyes that help them breathe while covered in sand. Image via David Clode/ Unsplash.
Be careful, some sea rays can sting
Many rays don’t even have a stinger, and those that have it use it as a defensive weapon. So these animals only use it when they feel attacked.
This stinger is located above the tail and is replaced by another from time to time. That’s why some rays have two or three stingers.
The stinger on some rays is poisonous and very dangerous. Even a newborn stingray already has poison in its stinger.
Some rays can sting, but they don’t attack unless they feel threatened. Image via David Clode/ Unsplash.
Electric rays
Some rays also produce electrical shocks. Electric rays spend much of the day camouflaged under the sand and go out to hunt at night. They emit electric shocks of up to 220 volts to defend themselves against predators or to stun their prey.
We are all electric in one way or another, but these rays have enhanced this characteristic with specialized organs. They produce their discharges from electric organs on either side of their head, the tail or near the tail, depending on the type of electric ray. Furthermore, they get to decide when to use them. They can generate several discharges in a row, but they lose strength.
Within the electric organs are cells called electrocytes arranged in stacked columns. Electrocytes are modified cells either of muscle (in most cases) or neural origin. These cells generate the electric punch. The number of electrocytes in a column and the number of columns dictate how much electricity the fish can produce.
Rays camouflage themselves in the sand of the sea to hunt. Image via Piermario Eva/ Unsplash.
Flotation system and feeding habits
The main factor that provides buoyancy to sharks and rays is their large liver (up to 25% of the body weight in some species).
Sharks and rays have teeth and cannot feed effectively with broken or worn teeth. Fortunately, they continue to shed and replace teeth throughout their lives.
Sea rays are dynamic hunters. They use a clever technique. Because of their flattened shape, they go to the bottom of the sea, move the sand with their fins to spread it over themselves and hide to catch their prey. Their favorite food is crustaceans, mollusks and small fish.
And here’s a curious fact. Since rays’ eyes are on the top of the body, but the mouth is on the bottom, it can be difficult for them to find their food. However, there is a lot of life on the seabed, and any unsuspecting animal turns out to be an excellent option.
Rays’ favorite food is crustaceans, mollusks and small fish. Image via David Clode/ Unsplash.
The ecosystem says thank you
Sea rays are valuable to ecosystems. When these animals move across the seafloor and move sand, they help build microhabitats for tiny creatures. In this way, they create homes for various small invertebrates. By doing this, they also help many other marine species feed on small fish.
In addition, rays are oxygen generators. Some rays can dive to almost 6,600 feet (2,000 meters) to feed. When they return to the surface, they defecate, depositing essential nutrients for phytoplankton. In case you didn’t know, phytoplankton produce half of Earth’s oxygen supply.
The ingredients necessary for phytoplankton to carry out photosynthesis are carbon dioxide, light and nutrients. The light is obtained directly from the sun. And since the ocean is an open system, it’s constantly exchanging carbon dioxide. But what about the nutrients? Well, they float on the surface, but they also sink due to gravity to the bottom of the ocean … And this is where our saviors, the rays, come in.
Rays are valuable to ecosystems. They help build microhabitats and are oxygen generators. Image via Diego Delso/ Wikipedia (CC BY-SA 4.0.).
An intelligent animal
Rays have a very large brain in relation to their body size. This superbrain is not only big but makes it quite intelligent. In fact, rays recognize themselves in the mirror, an ability they share with dolphins, primates and elephants, indicating high cognitive functions.
These incredibly intelligent animals can create mental maps of their underwater environment, a sign of their highly developed long-term memory.
Rays have big brains and are very smart. Image via David Clode/ Unsplash.
Manta rays are quite different from other sea rays, because they’re much larger, measuring up to 26 feet (8 m). Additionally, the front of the body of the manta ray is more prominent and they have a less circular silhouette. Manta rays have their mouths in the front, while the other rays have their mouths under the body.
Also, manta rays swim with their mouths wide open, drawing in zooplankton and krill. So, they feed primarily on planktonic organisms, but they also eat shrimp plus small and moderately sized fish.
Manta rays are much larger than common rays. They have a less circular silhouette and have their mouths in the front. Image via Andre Kaim/ Unsplash.
Here’s a look at a few of the 600 species of sea rays:
A spotted eagle ray. Image via Jacob Robertson/ Wikipedia (public domain).A shovelnose ray or guitarfish. Image via Jot Powers/ Wikipedia (CC BY-SA 2.0).A sawfish. Can you see their resemblance to sharks? Image via Flavia Brandi/ Wikipedia (CC BY-SA 2.0.).
Habitat
Sea rays are found around the world. Some rays live in fresh water systems. Most rays inhabit coastal waters close to shore. Only a few species, like manta rays, live in open oceans. There have even been cases of rays reaching rivers, although this is not common.
Bottom line: Sea rays are descendants of sharks. They have strong teeth and some can be dangerous with stingers or electric discharges.
Sea rays are flying-saucer-shaped fish with long tails that skim along the seafloor. Many people lump all sea rays together and call them stingrays, but not all sea rays sting. In fact, some don’t even have stingers. A stingray is just one type of sea ray. In total, there are some 600 species of sea ray!
Even without a stinger, rays can be dangerous. We couldn’t expect any less, considering they’re descendants of sharks. So, apart from having very strong teeth, some rays can sting, and some can even produce electric discharges.
Sea rays are descendants of sharks
Sea rays are closely related to sharks. Rays first appeared in the fossil record about 200 million years ago, about 200 million years after the first sharks. They are believed to have evolved from flattened shark species.
Both animals share the same general skeletal structure. But did you know neither sharks nor rays have bones? Instead they have cartilage, a light, flexible and strong connective tissue. This exceptional adaptation improves their maneuverability and resistance underwater.
Thus, the ray is a cartilaginous fish belonging to the Batoidea superorder. These animals are easy to recognize because they’re very flat and, in the vast majority of cases, have long, round fins to move quickly through the water, and long, thin tails.
Rays are cartilaginous fish that look very flat, have long, round fins and have a long, thin tail. Image via Enrique Ortega Miranda/ Unsplash.
A very peculiar anatomy
These animals have fins that surround their entire body. The pectoral fins form a large disc and begin at the back of the skull. These fins are always undulating because, if they didn’t, the animal would sink. The pelvic fins are quite small and are integrated behind the pectoral fins.
The tail can be short and robust or thin and elongated. However, most species have a fairly long and thin tail.
As they are fish, rays have gills to breathe. In fact, they have five pairs of gill slits in the lower part of their body.
In addition, at the top of their body, next to the eyes, are the so-called spiracles, which are often confused with the eyes. The spiracles help them breathe when they are half buried and camouflaged under the sand.
Rays have gills to breathe, but they also have spiracles next to the eyes that help them breathe while covered in sand. Image via David Clode/ Unsplash.
Be careful, some sea rays can sting
Many rays don’t even have a stinger, and those that have it use it as a defensive weapon. So these animals only use it when they feel attacked.
This stinger is located above the tail and is replaced by another from time to time. That’s why some rays have two or three stingers.
The stinger on some rays is poisonous and very dangerous. Even a newborn stingray already has poison in its stinger.
Some rays can sting, but they don’t attack unless they feel threatened. Image via David Clode/ Unsplash.
Electric rays
Some rays also produce electrical shocks. Electric rays spend much of the day camouflaged under the sand and go out to hunt at night. They emit electric shocks of up to 220 volts to defend themselves against predators or to stun their prey.
We are all electric in one way or another, but these rays have enhanced this characteristic with specialized organs. They produce their discharges from electric organs on either side of their head, the tail or near the tail, depending on the type of electric ray. Furthermore, they get to decide when to use them. They can generate several discharges in a row, but they lose strength.
Within the electric organs are cells called electrocytes arranged in stacked columns. Electrocytes are modified cells either of muscle (in most cases) or neural origin. These cells generate the electric punch. The number of electrocytes in a column and the number of columns dictate how much electricity the fish can produce.
Rays camouflage themselves in the sand of the sea to hunt. Image via Piermario Eva/ Unsplash.
Flotation system and feeding habits
The main factor that provides buoyancy to sharks and rays is their large liver (up to 25% of the body weight in some species).
Sharks and rays have teeth and cannot feed effectively with broken or worn teeth. Fortunately, they continue to shed and replace teeth throughout their lives.
Sea rays are dynamic hunters. They use a clever technique. Because of their flattened shape, they go to the bottom of the sea, move the sand with their fins to spread it over themselves and hide to catch their prey. Their favorite food is crustaceans, mollusks and small fish.
And here’s a curious fact. Since rays’ eyes are on the top of the body, but the mouth is on the bottom, it can be difficult for them to find their food. However, there is a lot of life on the seabed, and any unsuspecting animal turns out to be an excellent option.
Rays’ favorite food is crustaceans, mollusks and small fish. Image via David Clode/ Unsplash.
The ecosystem says thank you
Sea rays are valuable to ecosystems. When these animals move across the seafloor and move sand, they help build microhabitats for tiny creatures. In this way, they create homes for various small invertebrates. By doing this, they also help many other marine species feed on small fish.
In addition, rays are oxygen generators. Some rays can dive to almost 6,600 feet (2,000 meters) to feed. When they return to the surface, they defecate, depositing essential nutrients for phytoplankton. In case you didn’t know, phytoplankton produce half of Earth’s oxygen supply.
The ingredients necessary for phytoplankton to carry out photosynthesis are carbon dioxide, light and nutrients. The light is obtained directly from the sun. And since the ocean is an open system, it’s constantly exchanging carbon dioxide. But what about the nutrients? Well, they float on the surface, but they also sink due to gravity to the bottom of the ocean … And this is where our saviors, the rays, come in.
Rays are valuable to ecosystems. They help build microhabitats and are oxygen generators. Image via Diego Delso/ Wikipedia (CC BY-SA 4.0.).
An intelligent animal
Rays have a very large brain in relation to their body size. This superbrain is not only big but makes it quite intelligent. In fact, rays recognize themselves in the mirror, an ability they share with dolphins, primates and elephants, indicating high cognitive functions.
These incredibly intelligent animals can create mental maps of their underwater environment, a sign of their highly developed long-term memory.
Rays have big brains and are very smart. Image via David Clode/ Unsplash.
Manta rays are quite different from other sea rays, because they’re much larger, measuring up to 26 feet (8 m). Additionally, the front of the body of the manta ray is more prominent and they have a less circular silhouette. Manta rays have their mouths in the front, while the other rays have their mouths under the body.
Also, manta rays swim with their mouths wide open, drawing in zooplankton and krill. So, they feed primarily on planktonic organisms, but they also eat shrimp plus small and moderately sized fish.
Manta rays are much larger than common rays. They have a less circular silhouette and have their mouths in the front. Image via Andre Kaim/ Unsplash.
Here’s a look at a few of the 600 species of sea rays:
A spotted eagle ray. Image via Jacob Robertson/ Wikipedia (public domain).A shovelnose ray or guitarfish. Image via Jot Powers/ Wikipedia (CC BY-SA 2.0).A sawfish. Can you see their resemblance to sharks? Image via Flavia Brandi/ Wikipedia (CC BY-SA 2.0.).
Habitat
Sea rays are found around the world. Some rays live in fresh water systems. Most rays inhabit coastal waters close to shore. Only a few species, like manta rays, live in open oceans. There have even been cases of rays reaching rivers, although this is not common.
Bottom line: Sea rays are descendants of sharks. They have strong teeth and some can be dangerous with stingers or electric discharges.
We’ll reach the point in Earth’s orbit known as the June solstice this week, at 20:51 UTC (3:51 p.m. CDT) on June 20. Although no official world body has decreed it, most people nowadays will celebrate the start of Northern Hemisphere summer on this date, or Southern Hemisphere winter. What does this upcoming solstice mean to you? Short nights and long days? A high sun angle? Kids out of school? Summer fun time? Or does it bring winter for you? Join EarthSky’s Deborah Byrd, Marcy Curran and Dave Adalian LIVE, as we celebrate summer’s arrival! Watch LIVE at 17:15 UTC (12:15 p.m. CDT) Monday, June 17.
What does summer mean to you?
We asked on our social media pages what summer means to you, and you had lots to say. Check out some of your great answers and beautiful photos here. We’ll also share them during our livestream, so tune in.
Bottom line: What does summer mean to you? Here are some of the answers you shared with us on social media. And tune in to our livestream on Monday, June 17, at 12:15 p.m. CDT for more.
We’ll reach the point in Earth’s orbit known as the June solstice this week, at 20:51 UTC (3:51 p.m. CDT) on June 20. Although no official world body has decreed it, most people nowadays will celebrate the start of Northern Hemisphere summer on this date, or Southern Hemisphere winter. What does this upcoming solstice mean to you? Short nights and long days? A high sun angle? Kids out of school? Summer fun time? Or does it bring winter for you? Join EarthSky’s Deborah Byrd, Marcy Curran and Dave Adalian LIVE, as we celebrate summer’s arrival! Watch LIVE at 17:15 UTC (12:15 p.m. CDT) Monday, June 17.
What does summer mean to you?
We asked on our social media pages what summer means to you, and you had lots to say. Check out some of your great answers and beautiful photos here. We’ll also share them during our livestream, so tune in.
Bottom line: What does summer mean to you? Here are some of the answers you shared with us on social media. And tune in to our livestream on Monday, June 17, at 12:15 p.m. CDT for more.
Earth usually rides inside a protective bubble – the sphere of the sun’s influence – called the heliosphere. But a new study said that, for a brief period some 2 million years ago, the bubble might have shrunk. Earth might have been plunged out of the heliosphere, depicted here as the dark gray bubble on the right, over the backdrop of interstellar space. According to this new research, this change might have exposed Earth to high levels of radiation and influenced the climate. Image via Merav Opher/ Nature Astronomy/ BU.
Did Earth once lose its protective bubble?
Earth rides through our home galaxy, the Milky Way, inside a protective bubble around our sun. Scientists call this bubble the heliosphere. It’s essentially a cavity surrounding our local star, protecting our planet (and us) from the stronger radiation in the surrounding interstellar medium. But on June 10, 2024, a team of scientists said that, approximately 2 million years ago, the heliosphere might have shrunk. Earth might have been more directly exposed to the interstellar medium. These conditions might have left traces of heavier metals on Earth and could have cooled our climate for a time.
The culprit, the scientists said, was a cold cloud in space, made mostly of hydrogen atoms. That cloud crossed paths with our solar system. In fact, this cloud might have been so dense that it buffeted away the sun’s protective bubble.
Earth has gone through numerous ice ages, including the recent one we humans most often think of as the Ice Age. It happened during the Pleistocene period, some 2.6 million to a mere 11,700 years ago. To be sure, scientists have proposed many factors that might have contributed to earthly ice ages. But now, a team of scientists led by Merav Opher of Boston University has proposed another puzzle piece.
These researchers believe it was the sun’s location in our Milky Way galaxy that could also have contributed to the last earthly ice age. As our solar system encountered the interstellar cloud – and the bubble shrunk – the planets were exposed to the harsher conditions beyond the protective heliosphere. Opher said:
Stars move, and now this paper is showing not only that they move, but they encounter drastic changes.
Computer modeling the history of Earth
The scientists used computer modeling to look back in time and see where our solar system was in the past. In addition, the modeling also included something called the Local Ribbon of Cold Clouds system. This structure is a strand of immense, dense and super cold clouds made mostly of hydrogen atoms. And one of these clouds – the Local Lynx of Cold Cloud, near the end of the strand – might have collided with our solar system.
If that happened, then the sun’s protective bubble would have compressed and shrunk. Indeed, without the sun’s protective bubble, Earth and the other planets would have been exposed to radioactive particles. The particles are the leftovers of exploded stars, like iron and plutonium. In their paper, the researchers said increased amounts of isotopes of iron and plutonium in the geologic record align with this time period. Scientists have found these isotopes in Antarctic snow, ice cores … and on the moon.
The scientists said this exposure could have lasted from a couple hundred to a million years before the return of the protective bubble we live in today. Opher said:
This paper is the first to quantitatively show there was an encounter between the sun and something outside of the solar system that would have affected Earth’s climate.
This is a top-down view of the sun and inner solar system. The red ring represents the orbit of Earth. The yellow is the sun’s heliosphere being compressed from the left side, exposing Earth to the interstellar medium. Image via Merav Opher/ Nature Astronomy.
More clouds in our future
With this in mind, the scientists said it’s not possible to know exactly what effect a cold cloud would have had on our solar system. But Earth has likely encountered others in the past and will do so again in the future.
Now, the team is using data from the Gaia mission to look even farther back into the past. They’re trying to trace the location of the solar system and the cold cloud back 7 million years. Co-author Avi Loeb of Harvard University said:
Only rarely does our cosmic neighborhood beyond the solar system affect life on Earth. It is exciting to discover that our passage through dense clouds a few million years ago could have exposed the Earth to a much-larger flux of cosmic rays and hydrogen atoms. Our results open a new window into the relationship between the evolution of life on Earth and our cosmic neighborhood.
Bottom line: A team of scientists said that about 2 million years ago, the solar system might have collided with a cold cloud of interstellar gas and dust, shrinking the sun’s protective bubble and exposing Earth to space.
Earth usually rides inside a protective bubble – the sphere of the sun’s influence – called the heliosphere. But a new study said that, for a brief period some 2 million years ago, the bubble might have shrunk. Earth might have been plunged out of the heliosphere, depicted here as the dark gray bubble on the right, over the backdrop of interstellar space. According to this new research, this change might have exposed Earth to high levels of radiation and influenced the climate. Image via Merav Opher/ Nature Astronomy/ BU.
Did Earth once lose its protective bubble?
Earth rides through our home galaxy, the Milky Way, inside a protective bubble around our sun. Scientists call this bubble the heliosphere. It’s essentially a cavity surrounding our local star, protecting our planet (and us) from the stronger radiation in the surrounding interstellar medium. But on June 10, 2024, a team of scientists said that, approximately 2 million years ago, the heliosphere might have shrunk. Earth might have been more directly exposed to the interstellar medium. These conditions might have left traces of heavier metals on Earth and could have cooled our climate for a time.
The culprit, the scientists said, was a cold cloud in space, made mostly of hydrogen atoms. That cloud crossed paths with our solar system. In fact, this cloud might have been so dense that it buffeted away the sun’s protective bubble.
Earth has gone through numerous ice ages, including the recent one we humans most often think of as the Ice Age. It happened during the Pleistocene period, some 2.6 million to a mere 11,700 years ago. To be sure, scientists have proposed many factors that might have contributed to earthly ice ages. But now, a team of scientists led by Merav Opher of Boston University has proposed another puzzle piece.
These researchers believe it was the sun’s location in our Milky Way galaxy that could also have contributed to the last earthly ice age. As our solar system encountered the interstellar cloud – and the bubble shrunk – the planets were exposed to the harsher conditions beyond the protective heliosphere. Opher said:
Stars move, and now this paper is showing not only that they move, but they encounter drastic changes.
Computer modeling the history of Earth
The scientists used computer modeling to look back in time and see where our solar system was in the past. In addition, the modeling also included something called the Local Ribbon of Cold Clouds system. This structure is a strand of immense, dense and super cold clouds made mostly of hydrogen atoms. And one of these clouds – the Local Lynx of Cold Cloud, near the end of the strand – might have collided with our solar system.
If that happened, then the sun’s protective bubble would have compressed and shrunk. Indeed, without the sun’s protective bubble, Earth and the other planets would have been exposed to radioactive particles. The particles are the leftovers of exploded stars, like iron and plutonium. In their paper, the researchers said increased amounts of isotopes of iron and plutonium in the geologic record align with this time period. Scientists have found these isotopes in Antarctic snow, ice cores … and on the moon.
The scientists said this exposure could have lasted from a couple hundred to a million years before the return of the protective bubble we live in today. Opher said:
This paper is the first to quantitatively show there was an encounter between the sun and something outside of the solar system that would have affected Earth’s climate.
This is a top-down view of the sun and inner solar system. The red ring represents the orbit of Earth. The yellow is the sun’s heliosphere being compressed from the left side, exposing Earth to the interstellar medium. Image via Merav Opher/ Nature Astronomy.
More clouds in our future
With this in mind, the scientists said it’s not possible to know exactly what effect a cold cloud would have had on our solar system. But Earth has likely encountered others in the past and will do so again in the future.
Now, the team is using data from the Gaia mission to look even farther back into the past. They’re trying to trace the location of the solar system and the cold cloud back 7 million years. Co-author Avi Loeb of Harvard University said:
Only rarely does our cosmic neighborhood beyond the solar system affect life on Earth. It is exciting to discover that our passage through dense clouds a few million years ago could have exposed the Earth to a much-larger flux of cosmic rays and hydrogen atoms. Our results open a new window into the relationship between the evolution of life on Earth and our cosmic neighborhood.
Bottom line: A team of scientists said that about 2 million years ago, the solar system might have collided with a cold cloud of interstellar gas and dust, shrinking the sun’s protective bubble and exposing Earth to space.
Artist’s concept of the heliosphere, the sun’s region of influence in space. Scientists know relatively little about the shape of the heliosphere. Image via NASA/ The Conversation.
The sun warms the Earth, making it habitable for people and animals. But that’s not all it does, and it affects a much larger area of space. The heliosphere, the area of space influenced by the sun, is over a hundred times larger than the distance from the sun to the Earth.
The sun is a star that constantly emits a steady stream of plasma – highly energized ionized gas – called the solar wind. In addition to the constant solar wind, the sun also occasionally releases eruptions of plasma called coronal mass ejections, or CMEs. CMEs can contribute to the aurora. The sun also releases bursts of light and energy called flares.
The plasma coming off the sun expands through space, along with the sun’s magnetic field. Together they form the heliosphere, which lies within the surrounding local interstellar medium. And the interstellar medium is the plasma, neutral particles and dust that fill the space between stars and their respective astrospheres. Heliophysicists like me want to understand the heliosphere and how it interacts with the interstellar medium.
The eight known planets in the solar system, the asteroid belt between Mars and Jupiter, and the Kuiper Belt – the band of celestial objects beyond Neptune that includes the planetoid Pluto – all reside within the heliosphere. The heliosphere is so large that objects in the Kuiper Belt orbit closer to the sun than to the closest boundary of the heliosphere.
Artist’s concept of the heliosphere and its place in the local interstellar medium and in the Milky Way galaxy. An interstellar probe could travel farther than any previous spacecraft and help scientists get a good look at our heliosphere – the sun’s influence in space – from the outside. Image via JHU/APL.
Heliosphere protection
As distant stars explode, they expel large amounts of radiation into interstellar space in the form of highly energized particles known as cosmic rays. These cosmic rays can be dangerous for living organisms and can damage electronic devices and spacecraft.
Earth’s atmosphere protects life on the planet from the effects of cosmic radiation. But, even before that, the heliosphere itself acts as a cosmic shield from most interstellar radiation.
In addition to cosmic radiation, neutral particles and dust stream steadily into the heliosphere from the local interstellar medium. These particles can affect the space around Earth. They may even alter how the solar wind reaches the Earth.
Supernovae and the interstellar medium may have also influenced the origins of life and the evolution of humans on Earth. Some researchers predict that millions of years ago, the heliosphere came into contact with a cold, dense particle cloud in the interstellar medium that caused the heliosphere to shrink. Thus, for a time Earth may have been exposed to the local interstellar medium.
An unknown shape
But scientists don’t really know what the heliosphere’s shape is. Models range in shape from spherical to cometlike to croissant-shaped. These predictions vary in size by hundreds to thousands of times the distance from the sun to the Earth.
Scientists have, however, defined the direction that the sun is moving as the “nose” direction and the opposing direction as the “tail” direction. The nose direction should have the shortest distance to the heliopause, the boundary between the heliosphere and the local interstellar medium.
No probe has ever gotten a good look at the heliosphere from the outside or properly sampled the local interstellar medium. Doing so could tell scientists more about the heliosphere’s shape and its interaction with the local interstellar medium, the space environment beyond the heliosphere.
Crossing the heliopause with Voyager
In 1977, NASA launched the Voyager mission. Its two spacecraft flew past Jupiter, Saturn, Uranus and Neptune in the outer solar system. Scientists have determined that after observing these gas giants, the probes separately crossed the heliopause and into interstellar space in 2012 and 2018, respectively.
While Voyager 1 and 2 are the only probes to have ever potentially crossed the heliopause, they are well beyond their intended mission lifetimes. They can no longer return the necessary data as their instruments slowly fail or power down.
These spacecraft were designed to study planets, not the interstellar medium. This means they don’t have the right instruments to take all the measurements of the interstellar medium or the heliosphere that scientists need.
That’s where a potential interstellar probe mission could come in. A probe designed to fly beyond the heliopause would help scientists understand the heliosphere by observing it from the outside.
The Voyager spacecraft will no longer be able to provide data from interstellar space long before an interstellar probe exits the heliosphere. And once the probe is launched, depending on the trajectory, it will take about 50 or more years to reach the interstellar medium. This means the longer NASA waits to launch a probe, the longer scientists will be left with no missions operating in the outer heliosphere or the local interstellar medium.
NASA is considering developing an interstellar probe. This probe would take measurements of the plasma and magnetic fields in the interstellar medium and image the heliosphere from the outside. To prepare, NASA asked for input from more than 1,000 scientists on a mission concept.
The initial report recommended the probe travel on a trajectory that is about 45 degrees away from the heliosphere’s nose direction. This trajectory would retrace part of Voyager’s path, while reaching some new regions of space. This way, scientists could study new regions and revisit some partly known regions of space.
This path would give the probe only a partly angled view of the heliosphere, and it wouldn’t be able to see the heliotail, the region scientists know the least about.
The heliotail
In the heliotail, scientists predict the plasma that makes up the heliosphere mixes with the plasma that makes up the interstellar medium. This happens through a process called magnetic reconnection, which allows charged particles to stream from the local interstellar medium into the heliosphere. Just like the neutral particles entering through the nose, these particles affect the space environment within the heliosphere.
In this case, however, the particles have a charge and can interact with solar and planetary magnetic fields. While these interactions occur at the boundaries of the heliosphere, very far from Earth, they affect the makeup of the heliosphere’s interior.
How a probe could study it
In a new study published in Frontiers in Astronomy and Space Sciences, my colleagues and I evaluated six potential launch directions ranging from the nose to the tail. We found that rather than exiting close to the nose direction, a trajectory intersecting the heliosphere’s flank toward the tail direction would give the best perspective on the heliosphere’s shape.
A trajectory along this direction would present scientists with a unique opportunity to study a completely new region of space within the heliosphere. When the probe exits the heliosphere into interstellar space, it would get a view of the heliosphere from the outside at an angle that would give scientists a more detailed idea of its shape, especially in the disputed tail region.
In the end, whichever direction an interstellar probe launches, the science it returns will be invaluable and quite literally astronomical.
Bottom line: The heliosphere is a bubble of gas surrounding the sun. It extends outward and protects the planets from interstellar radiation. But how big is the heliosphere?
Artist’s concept of the heliosphere, the sun’s region of influence in space. Scientists know relatively little about the shape of the heliosphere. Image via NASA/ The Conversation.
The sun warms the Earth, making it habitable for people and animals. But that’s not all it does, and it affects a much larger area of space. The heliosphere, the area of space influenced by the sun, is over a hundred times larger than the distance from the sun to the Earth.
The sun is a star that constantly emits a steady stream of plasma – highly energized ionized gas – called the solar wind. In addition to the constant solar wind, the sun also occasionally releases eruptions of plasma called coronal mass ejections, or CMEs. CMEs can contribute to the aurora. The sun also releases bursts of light and energy called flares.
The plasma coming off the sun expands through space, along with the sun’s magnetic field. Together they form the heliosphere, which lies within the surrounding local interstellar medium. And the interstellar medium is the plasma, neutral particles and dust that fill the space between stars and their respective astrospheres. Heliophysicists like me want to understand the heliosphere and how it interacts with the interstellar medium.
The eight known planets in the solar system, the asteroid belt between Mars and Jupiter, and the Kuiper Belt – the band of celestial objects beyond Neptune that includes the planetoid Pluto – all reside within the heliosphere. The heliosphere is so large that objects in the Kuiper Belt orbit closer to the sun than to the closest boundary of the heliosphere.
Artist’s concept of the heliosphere and its place in the local interstellar medium and in the Milky Way galaxy. An interstellar probe could travel farther than any previous spacecraft and help scientists get a good look at our heliosphere – the sun’s influence in space – from the outside. Image via JHU/APL.
Heliosphere protection
As distant stars explode, they expel large amounts of radiation into interstellar space in the form of highly energized particles known as cosmic rays. These cosmic rays can be dangerous for living organisms and can damage electronic devices and spacecraft.
Earth’s atmosphere protects life on the planet from the effects of cosmic radiation. But, even before that, the heliosphere itself acts as a cosmic shield from most interstellar radiation.
In addition to cosmic radiation, neutral particles and dust stream steadily into the heliosphere from the local interstellar medium. These particles can affect the space around Earth. They may even alter how the solar wind reaches the Earth.
Supernovae and the interstellar medium may have also influenced the origins of life and the evolution of humans on Earth. Some researchers predict that millions of years ago, the heliosphere came into contact with a cold, dense particle cloud in the interstellar medium that caused the heliosphere to shrink. Thus, for a time Earth may have been exposed to the local interstellar medium.
An unknown shape
But scientists don’t really know what the heliosphere’s shape is. Models range in shape from spherical to cometlike to croissant-shaped. These predictions vary in size by hundreds to thousands of times the distance from the sun to the Earth.
Scientists have, however, defined the direction that the sun is moving as the “nose” direction and the opposing direction as the “tail” direction. The nose direction should have the shortest distance to the heliopause, the boundary between the heliosphere and the local interstellar medium.
No probe has ever gotten a good look at the heliosphere from the outside or properly sampled the local interstellar medium. Doing so could tell scientists more about the heliosphere’s shape and its interaction with the local interstellar medium, the space environment beyond the heliosphere.
Crossing the heliopause with Voyager
In 1977, NASA launched the Voyager mission. Its two spacecraft flew past Jupiter, Saturn, Uranus and Neptune in the outer solar system. Scientists have determined that after observing these gas giants, the probes separately crossed the heliopause and into interstellar space in 2012 and 2018, respectively.
While Voyager 1 and 2 are the only probes to have ever potentially crossed the heliopause, they are well beyond their intended mission lifetimes. They can no longer return the necessary data as their instruments slowly fail or power down.
These spacecraft were designed to study planets, not the interstellar medium. This means they don’t have the right instruments to take all the measurements of the interstellar medium or the heliosphere that scientists need.
That’s where a potential interstellar probe mission could come in. A probe designed to fly beyond the heliopause would help scientists understand the heliosphere by observing it from the outside.
The Voyager spacecraft will no longer be able to provide data from interstellar space long before an interstellar probe exits the heliosphere. And once the probe is launched, depending on the trajectory, it will take about 50 or more years to reach the interstellar medium. This means the longer NASA waits to launch a probe, the longer scientists will be left with no missions operating in the outer heliosphere or the local interstellar medium.
NASA is considering developing an interstellar probe. This probe would take measurements of the plasma and magnetic fields in the interstellar medium and image the heliosphere from the outside. To prepare, NASA asked for input from more than 1,000 scientists on a mission concept.
The initial report recommended the probe travel on a trajectory that is about 45 degrees away from the heliosphere’s nose direction. This trajectory would retrace part of Voyager’s path, while reaching some new regions of space. This way, scientists could study new regions and revisit some partly known regions of space.
This path would give the probe only a partly angled view of the heliosphere, and it wouldn’t be able to see the heliotail, the region scientists know the least about.
The heliotail
In the heliotail, scientists predict the plasma that makes up the heliosphere mixes with the plasma that makes up the interstellar medium. This happens through a process called magnetic reconnection, which allows charged particles to stream from the local interstellar medium into the heliosphere. Just like the neutral particles entering through the nose, these particles affect the space environment within the heliosphere.
In this case, however, the particles have a charge and can interact with solar and planetary magnetic fields. While these interactions occur at the boundaries of the heliosphere, very far from Earth, they affect the makeup of the heliosphere’s interior.
How a probe could study it
In a new study published in Frontiers in Astronomy and Space Sciences, my colleagues and I evaluated six potential launch directions ranging from the nose to the tail. We found that rather than exiting close to the nose direction, a trajectory intersecting the heliosphere’s flank toward the tail direction would give the best perspective on the heliosphere’s shape.
A trajectory along this direction would present scientists with a unique opportunity to study a completely new region of space within the heliosphere. When the probe exits the heliosphere into interstellar space, it would get a view of the heliosphere from the outside at an angle that would give scientists a more detailed idea of its shape, especially in the disputed tail region.
In the end, whichever direction an interstellar probe launches, the science it returns will be invaluable and quite literally astronomical.
Bottom line: The heliosphere is a bubble of gas surrounding the sun. It extends outward and protects the planets from interstellar radiation. But how big is the heliosphere?
Tonight, find the Dragon’s Eyes. For years, I’ve glanced up to the north on June evenings and spied the two stars marked on today’s chart, Rastaban and Eltanin in the constellation Draco. They’re noticeable because they’re relatively bright and near each other. There’s always that split second when I ask myself with some excitement what two stars are those? It’s then that my eyes drift to blue-white Vega nearby … and I know, by Vega’s nearness, that they are the stars Rastaban and Eltanin.
These two stars represent the fiery eyes of the constellation Draco the Dragon. Moreover, these stars nearly mark the radiant point for the annual October Draconid meteor shower.
Because the stars stay fixed relative to each other, Vega is always near these stars. Vega, by the way, lodges at the apex of the Summer Triangle, a famous pattern consisting of three bright stars in three separate constellations, also prominent at this time of the year.
Rastaban and Eltanin from around the globe
From tropical and subtropical latitudes in the Southern Hemisphere, the stars Rastaban and Eltanin shine quite low in the northern sky (below Vega). In either hemisphere, at all time zones, the Dragon’s eyes climb highest up in the sky around midnight (1 a.m. daylight saving time) in mid-June, 11 p.m. (midnight daylight saving time) in early July, and 9 p.m. (10 p.m. daylight saving time) in early August. But from temperate latitudes in the Southern Hemisphere (southern Australia and New Zealand), the Dragon’s eyes never climb above your horizon. However, you can catch the star Vega way low in your northern sky.
People at mid-northern latitudes get to view the Dragon’s eyes all night long!
About constellations
Speaking of Rastaban and Eltanin, one of you asked:
What are constellations?
The answer is that they’re patterns of stars on the sky’s dome. The Greeks and Romans, for example, named them for their gods and goddesses, and also for many sorts of animals. In the 20th century, the International Astronomical Union (IAU) formalized the names and boundaries of the constellations. Now every star in the sky belongs to one or another constellation.
The stars within constellations aren’t connected, except in the mind’s eye of stargazers. The stars in general lie at vastly different distances from Earth. It’s by finding juxtaposed patterns on the sky’s dome that you’ll come to know the constellations, much as I identify Rastaban and Eltanin at this time of the year by looking for the star Vega.
The constellation Draco from Urania’s Mirror by Sidney Hall. Image via Wikimedia Commons.
Bottom line: Look in the northeast on these June evenings, near the star Vega. You’ll see Rastaban and Eltanin, two stars that are bright and close together.
Tonight, find the Dragon’s Eyes. For years, I’ve glanced up to the north on June evenings and spied the two stars marked on today’s chart, Rastaban and Eltanin in the constellation Draco. They’re noticeable because they’re relatively bright and near each other. There’s always that split second when I ask myself with some excitement what two stars are those? It’s then that my eyes drift to blue-white Vega nearby … and I know, by Vega’s nearness, that they are the stars Rastaban and Eltanin.
These two stars represent the fiery eyes of the constellation Draco the Dragon. Moreover, these stars nearly mark the radiant point for the annual October Draconid meteor shower.
Because the stars stay fixed relative to each other, Vega is always near these stars. Vega, by the way, lodges at the apex of the Summer Triangle, a famous pattern consisting of three bright stars in three separate constellations, also prominent at this time of the year.
Rastaban and Eltanin from around the globe
From tropical and subtropical latitudes in the Southern Hemisphere, the stars Rastaban and Eltanin shine quite low in the northern sky (below Vega). In either hemisphere, at all time zones, the Dragon’s eyes climb highest up in the sky around midnight (1 a.m. daylight saving time) in mid-June, 11 p.m. (midnight daylight saving time) in early July, and 9 p.m. (10 p.m. daylight saving time) in early August. But from temperate latitudes in the Southern Hemisphere (southern Australia and New Zealand), the Dragon’s eyes never climb above your horizon. However, you can catch the star Vega way low in your northern sky.
People at mid-northern latitudes get to view the Dragon’s eyes all night long!
About constellations
Speaking of Rastaban and Eltanin, one of you asked:
What are constellations?
The answer is that they’re patterns of stars on the sky’s dome. The Greeks and Romans, for example, named them for their gods and goddesses, and also for many sorts of animals. In the 20th century, the International Astronomical Union (IAU) formalized the names and boundaries of the constellations. Now every star in the sky belongs to one or another constellation.
The stars within constellations aren’t connected, except in the mind’s eye of stargazers. The stars in general lie at vastly different distances from Earth. It’s by finding juxtaposed patterns on the sky’s dome that you’ll come to know the constellations, much as I identify Rastaban and Eltanin at this time of the year by looking for the star Vega.
The constellation Draco from Urania’s Mirror by Sidney Hall. Image via Wikimedia Commons.
Bottom line: Look in the northeast on these June evenings, near the star Vega. You’ll see Rastaban and Eltanin, two stars that are bright and close together.
