Welcome to my blog "Mystery of Galaxy".
Today our topic is on a mysterious planet of our solar system "Planet 9".Astronomers believe there is a giant planet lurking in the outer solar system, and we're going to learn more about it starting right now.
In 2016, astronomers Mike Brown and Konstantin Batygin at Caltech announced evidence of a giant planet in the distant outer solar system. In this article, we'd like to tell you about how they arrived at this claim and where we stand on the hunt for Planet 9. Now claims of new planets in our solar system are nothing new. In 1906, Percival Lowell believed that there was a giant planet that was disturbing the orbits of Uranus and Neptune. Lowell calculated that the planet must be at least the mass of Jupiter but perhaps even larger. He spent the last decade of his life searching for Planet X to no avail. When Clyde Tombaugh discovered Pluto in 1930. People thought that Lowell's giant planet was found. But Pluto wasn't a giant. In fact it's not even a Mercury sized planet. Pluto turned out to be a member of a new region of trans-Neptunian objects called the Kuiper belt.
As for Lowell's calculations, well, it turns out he was wrong. He used the wrong values for the masses of Neptune and Uranus, and when Voyager 2 flew past both planets in the 1980s, their masses were precisely calculated and the perturbances of the other orbits that Lowell discovered went away. Still that didn't stop astronomers from invoking Planet X on 573 different occasions, only to find that claim disproven on every single attempt.
Why are astronomers so convinced that there is a new planet out there?
In order to understand that, we need to go back to 2003 when Mike Brown and his colleagues discovered Sedna.
It's a 1000 kilometer-wide dwarf planet that orbits far beyond Neptune. But Sedna's orbit isn't just far, it's shaped differently than anything that had been discovered before. Sedna has a close approach to the Sun - or perihelion - of 76 astronomical units, and swings out to an aphelion of 934 astronomical units. This highly eccentric orbit was unlike anything that we'd had ever discovered in the solar system before, and astronomers immediately wanted to know just what Sedna was doing out there on such a strange orbit. In 2014 Chad Trujillo and Scott Sheppard discovered that a new object, 2012 VP 113,
was also on a really eccentric orbit that was not unlike Sedna's. Both of these objects are so distant that they are completely oblivious to the gravity of the inner planets. In other words, they're detached from the rest of the solar system. Soon additional objects were discovered that are a little closer to the Kuiper belt but are otherwise on very eccentric orbits like the Sednoids. But there was something else really peculiar about these objects: not only were their orbits eccentric but they were all pointing in roughly the same direction. Mike Brown and Konstantin Batygin analyzed these orbits and they discovered that not only were they aligned but they were also inclined by roughly the same amount with respect to the rest of the solar system. In fact they even calculated that the chances of these alignments occurring by random chance were something like 0.007%. They concluded that something must be shepherding the orbits of these objects. And that something turns out to be a giant planet about 10 times Earth's mass on a 10,000 to 20,000 year orbit around the Sun. They dubbed this new world "Planet 9". But they also realized something else: over time Planet 9 could twist up the orbits of inner Kuiper belt objects and fling them into highly eccentric perpendicular orbits to the rest of the solar system. Sure enough, a population of exactly those types of objects on exactly those types of orbits were discovered year prior.
Planet 9 explained something else that has puzzled astronomers for a very longtime about our solar system: all of the planets orbit the Sun and roughly the same plane, inclined by about degree of each other. But the Sun is tilted by about six degrees, and that's a significant shift from the plane of the planets. But Planet 9's orbit is highly inclined with respect to the solar system. That means that Planet nine can act as a kind of a lever arm, and gradually tilt the orbits of the planets. In other words, it's not the Sun that's tilted but the orbits of the planets themselves that have been tilted, courtesy of Planet nine. And Planet nine gives our solar system something that we didn't even realize we were missing until relatively recently. In 2000 planetary systems have been discovered so far with planets ranging in size from smaller than Mars to larger than Jupiter. But the most common type of planet found to date ranges in size between Earth and Neptune. These are called "Super Earths", and we don't seem to have anything like that in our solar system. But now with Planet 9 we do! Planet 9 is estimated to be about 10 times Earth's mass which would put it firmly in the super-Earth category.
Why would our super-Earth be so far away from the rest of the other planets?
It turns out that if you simulate the early solar system with four giant cores, you end up with the four giant planets that you have today. But if you simulate five giant cores forming in the early solar system, the least massive of these cores gets ejected while the remaining four cores goes on to form the four giant planets. The ejected core's growth is stunted and it only grows to about ten Earth masses. So Planet 9 explains so much about our solar system. It explains the orbital clustering of distant outer bodies. It explains the apparent tilt of the Sun. It even gives our solar system its very own super-Earth. Only one teeny little problem is that we haven't actually found Planet 9 yet. But astronomers are looking for it, and the good news is that they're pretty sure it should be found somewhere near the constellation Orion. The bad news is that it's still an enormous chunk of the sky to have to search through, so astronomers have formed teams in a friendly competition to see who can find planet nine first. And in October 2018, Scott Sheppard and Chad Trujillo announced that a new object in the outer solar system has an orbit that fits perfectly into the Planet 9 model. This object is called 2015 TG387, and because it was discovered near Halloween and because of "TG" in its name, it's been nicknamed "The Goblin".
The Goblin is tiny, only 300 kilometers across and is most likely a frozen chunk of ammonia and methane ice. The Goblin's orbit is the largest and most eccentric of any object of its kind ever discovered. Its perihelion is "only" 65 au, so it does come in a little bit closer than Sedna. But its wings out to an aphelion of, get this, 2,300 au, making this the most distant object of its type ever discovered. And best of all, The Goblin's orbit is exactly where it would be expected to be if it were being shepherded by Planet 9. And it gets even better because astronomers have found another set of objects in orbits that are anti-aligned with the previous orbits, but they would fit perfectly inside of Planet 9's predicted orbit, allowing it to be held stable by the giant planet. Now all this makes for some compelling evidence that there is a distant giant planet lurking in the outer solar system. and we're going to learn how astronomers are searching for Planet 9.
An examination of recent surveys showed no evidence for such a planet. This suggests that Planet Nine is probably near its farthest point from the Sun, or aphelion. And that makes sense because as planets approach perihelion, they speed up, whereas when they approach aphelion, they slow down. Planet Nine should therefore spend most of its 20,000 year orbit near aphelion. But its aphelion distance could be as much as 1,000 astronomical units. At that distance, Planet Nine would be25,000 times fainter than Pluto. Telescopes like Keck and Hubble should have no trouble spotting Planet Nine, but their fields of view are incredibly small, and the search area in Taurus and Orion is something like 4,000 times the size of the full Moon.
So using Keck or Hubble would be like squinting through a soda straw. But there is a telescope that's right next door to Keck. It's the 8.2 meter, Subaru telescope,
the national telescope of Japan. Subaru is equipped with the Hyper Suprime-Cam, an 870 megapixel camera that can capture 6 full moons’ worth of sky in a single image. Planet Nine's aphelion should be somewhere between the constellations Orion and Taurus, making the search area visible from September through February of every year. Subaru should be able to cover the search area in about 20 nights. That may not seem like a lot of time, but astronomers using Subaru to search for Planet Nine have to compete with other astronomers for time on the telescope. Not only that but, bad weather interfered with the first two years of Planet Nine searching, so only a fraction of the search area has been covered to date. At this rate, it'll probably take a few more years before the entire Planet Nine search area is completely covered. .
Luckily, a second team of astronomers led by Scott Sheppard from Carnegie Science are also using Subaru to conduct their own search for Planet Nine. Even better, Sheppard’s team are also piggybacking on another survey with another telescope. The Dark Energy Survey uses the 4-meter Victor Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile.
The telescope used the Dark Energy Camera, or DE Cam mounted at the telescope's prime focus. DE Cam’s field of view is twice the Hyper Supreme-Cam mounted on the Subaru telescope. But its detector is 300 megapixels smaller and it's mounted to a telescope that is half the size of Subaru. Even so, Sheppard and his team used the Blanco telescope to discover several new trans-Neptunian objects that are even fainter than Planet Nine is predicted to be. So this tells us that the search for Planet Nine is in fact possible. And by the way, these objects all follow orbits that are clustered in a manner that is consistent with Planet Nine.
Now you may be wondering how is it they keep finding these tiny objects when there's supposedly a giant planet they haven't found yet?
Well the answer is we expect there to be thousands, maybe even hundreds of thousands of these tiny objects, but only one giant planet. It's like going fishing in the ocean - you expect to catch a lot of small fish, but you don't expect to catch a whale. But what if neither the Subaru nor Blanco telescopes find Planet Nine? That would be unfortunate, but it wouldn’t necessarily rule out the planet's existence. It could mean it's simply on a different part of its orbit, so a different region of the sky would need to be searched. Or it could be that Planet Nine is on a much larger orbit than predicted, and its aphelion would carry it farther away, making it too faint to be detected by Subaru. But there is another possibility which kind gives us the screaming heebie-jeebies. Planet Nine could be passing in front of the Milky Way, lost in the glare of a crowded field of bright background stars. Fortunately, there’s a telescope under construction that should be able to resolve Planet Nine even among such a crowded field. The Large Synoptic Survey Telescope will make the widest and deepest scan of the southern sky over the course of a decade.
LSST will be armed with an 8.4 meter mirror, and a gigantic, 3 Gigapixel camera with a 9.6 square degree field of view. That will give LSST the sensitivity and clarity to distinguish Planet Nine even if it’s fainter than expected, and even if it’s passing across the Milky Way. Not only that, but LSST will complete a full scan of the entire sky once every five to seven days and repeat over and over again for a decade. That means that every point in the sky will be imaged by LSST more than 800 times. This means that if Planet Nine is on a completely different orbit, or if it's farther and fainter than expected, LSST should be able to detect it as long as it's somewhere in the southern sky. Meanwhile, the search for Planet Nine continues. It's November 2018, and Mike Brown and his team have time scheduled on Subaru in December. This will mark the third year searching for Planet Nine, and hopefully a little bit more of the sky will be covered. But each year brings new discoveries of distant objects in the outer solar system, each of which seem to be pointing the way to Planet Nine. There are so many new worlds waiting to be discovered, both right here in our solar system and far beyond. that's all thank you.
Today our topic is on a mysterious planet of our solar system "Planet 9".Astronomers believe there is a giant planet lurking in the outer solar system, and we're going to learn more about it starting right now.
In 2016, astronomers Mike Brown and Konstantin Batygin at Caltech announced evidence of a giant planet in the distant outer solar system. In this article, we'd like to tell you about how they arrived at this claim and where we stand on the hunt for Planet 9. Now claims of new planets in our solar system are nothing new. In 1906, Percival Lowell believed that there was a giant planet that was disturbing the orbits of Uranus and Neptune. Lowell calculated that the planet must be at least the mass of Jupiter but perhaps even larger. He spent the last decade of his life searching for Planet X to no avail. When Clyde Tombaugh discovered Pluto in 1930. People thought that Lowell's giant planet was found. But Pluto wasn't a giant. In fact it's not even a Mercury sized planet. Pluto turned out to be a member of a new region of trans-Neptunian objects called the Kuiper belt.
 |
| Kuiper belt Source: NASA/JHUAPL/SwRI/Magda Saina / Public domain |
As for Lowell's calculations, well, it turns out he was wrong. He used the wrong values for the masses of Neptune and Uranus, and when Voyager 2 flew past both planets in the 1980s, their masses were precisely calculated and the perturbances of the other orbits that Lowell discovered went away. Still that didn't stop astronomers from invoking Planet X on 573 different occasions, only to find that claim disproven on every single attempt.
Why are astronomers so convinced that there is a new planet out there?
In order to understand that, we need to go back to 2003 when Mike Brown and his colleagues discovered Sedna.
 |
| Sedna Source: NASA/JPL-Caltech/R. Hurt (SSC-Caltech) / Public domain |
It's a 1000 kilometer-wide dwarf planet that orbits far beyond Neptune. But Sedna's orbit isn't just far, it's shaped differently than anything that had been discovered before. Sedna has a close approach to the Sun - or perihelion - of 76 astronomical units, and swings out to an aphelion of 934 astronomical units. This highly eccentric orbit was unlike anything that we'd had ever discovered in the solar system before, and astronomers immediately wanted to know just what Sedna was doing out there on such a strange orbit. In 2014 Chad Trujillo and Scott Sheppard discovered that a new object, 2012 VP 113,
 |
| VP 113 and its orbit Source: Tomruen / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0) |
was also on a really eccentric orbit that was not unlike Sedna's. Both of these objects are so distant that they are completely oblivious to the gravity of the inner planets. In other words, they're detached from the rest of the solar system. Soon additional objects were discovered that are a little closer to the Kuiper belt but are otherwise on very eccentric orbits like the Sednoids. But there was something else really peculiar about these objects: not only were their orbits eccentric but they were all pointing in roughly the same direction. Mike Brown and Konstantin Batygin analyzed these orbits and they discovered that not only were they aligned but they were also inclined by roughly the same amount with respect to the rest of the solar system. In fact they even calculated that the chances of these alignments occurring by random chance were something like 0.007%. They concluded that something must be shepherding the orbits of these objects. And that something turns out to be a giant planet about 10 times Earth's mass on a 10,000 to 20,000 year orbit around the Sun. They dubbed this new world "Planet 9". But they also realized something else: over time Planet 9 could twist up the orbits of inner Kuiper belt objects and fling them into highly eccentric perpendicular orbits to the rest of the solar system. Sure enough, a population of exactly those types of objects on exactly those types of orbits were discovered year prior.
Planet 9 explained something else that has puzzled astronomers for a very longtime about our solar system: all of the planets orbit the Sun and roughly the same plane, inclined by about degree of each other. But the Sun is tilted by about six degrees, and that's a significant shift from the plane of the planets. But Planet 9's orbit is highly inclined with respect to the solar system. That means that Planet nine can act as a kind of a lever arm, and gradually tilt the orbits of the planets. In other words, it's not the Sun that's tilted but the orbits of the planets themselves that have been tilted, courtesy of Planet nine. And Planet nine gives our solar system something that we didn't even realize we were missing until relatively recently. In 2000 planetary systems have been discovered so far with planets ranging in size from smaller than Mars to larger than Jupiter. But the most common type of planet found to date ranges in size between Earth and Neptune. These are called "Super Earths", and we don't seem to have anything like that in our solar system. But now with Planet 9 we do! Planet 9 is estimated to be about 10 times Earth's mass which would put it firmly in the super-Earth category.
Why would our super-Earth be so far away from the rest of the other planets?
It turns out that if you simulate the early solar system with four giant cores, you end up with the four giant planets that you have today. But if you simulate five giant cores forming in the early solar system, the least massive of these cores gets ejected while the remaining four cores goes on to form the four giant planets. The ejected core's growth is stunted and it only grows to about ten Earth masses. So Planet 9 explains so much about our solar system. It explains the orbital clustering of distant outer bodies. It explains the apparent tilt of the Sun. It even gives our solar system its very own super-Earth. Only one teeny little problem is that we haven't actually found Planet 9 yet. But astronomers are looking for it, and the good news is that they're pretty sure it should be found somewhere near the constellation Orion. The bad news is that it's still an enormous chunk of the sky to have to search through, so astronomers have formed teams in a friendly competition to see who can find planet nine first. And in October 2018, Scott Sheppard and Chad Trujillo announced that a new object in the outer solar system has an orbit that fits perfectly into the Planet 9 model. This object is called 2015 TG387, and because it was discovered near Halloween and because of "TG" in its name, it's been nicknamed "The Goblin".
 |
| The Goblin(2015 TG387) Source: Ortsed04 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0) |
The Goblin is tiny, only 300 kilometers across and is most likely a frozen chunk of ammonia and methane ice. The Goblin's orbit is the largest and most eccentric of any object of its kind ever discovered. Its perihelion is "only" 65 au, so it does come in a little bit closer than Sedna. But its wings out to an aphelion of, get this, 2,300 au, making this the most distant object of its type ever discovered. And best of all, The Goblin's orbit is exactly where it would be expected to be if it were being shepherded by Planet 9. And it gets even better because astronomers have found another set of objects in orbits that are anti-aligned with the previous orbits, but they would fit perfectly inside of Planet 9's predicted orbit, allowing it to be held stable by the giant planet. Now all this makes for some compelling evidence that there is a distant giant planet lurking in the outer solar system. and we're going to learn how astronomers are searching for Planet 9.
Search missions for find Planet 9
There is evidence of a giant planet lurking in the outer solar system at more than a thousand times the distance from the Sun as Earth, and could be as much as 25,000 times fainter than Pluto. Astronomers are gazing into the abyss in search of Planet Nine. And this planet would explain the orbital clustering of several trans-Neptunian objects. However, evidence of a planet is not nearly as good as finding the planet itself. now we're going to talk about how astronomers are doing just that. Mike Brown and Konstantin Batygin of Caltech ran several computer simulations to determine what kinds of orbits Planet Nine could have. But all of them are highly elongated and tend to point away from the clustered objects. That means from our vantage point here on Earth, Planet Nine’s possible orbits are confined to a band encircling us around the sky. Even so, this band is a really large search area. Fortunately, there are some clues that help us narrow down where in the sky to search. Planet Nine is estimated to be about 10 times more massive than Earth, and comes no closer than about 300 astronomical units to the Sun. Even though that's 10 times farther from the Sun than Neptune, Planet Nine should still have been bright enough to have been detected in previous surveys.An examination of recent surveys showed no evidence for such a planet. This suggests that Planet Nine is probably near its farthest point from the Sun, or aphelion. And that makes sense because as planets approach perihelion, they speed up, whereas when they approach aphelion, they slow down. Planet Nine should therefore spend most of its 20,000 year orbit near aphelion. But its aphelion distance could be as much as 1,000 astronomical units. At that distance, Planet Nine would be25,000 times fainter than Pluto. Telescopes like Keck and Hubble should have no trouble spotting Planet Nine, but their fields of view are incredibly small, and the search area in Taurus and Orion is something like 4,000 times the size of the full Moon.
 |
| Keck observatories Source: NASA/JPL / Public domain |
 |
| Hubble telescope |
So using Keck or Hubble would be like squinting through a soda straw. But there is a telescope that's right next door to Keck. It's the 8.2 meter, Subaru telescope,
 |
| Subaru telescope Source;Denys (fr) / CC BY (https://creativecommons.org/licenses/by/3.0) |
the national telescope of Japan. Subaru is equipped with the Hyper Suprime-Cam, an 870 megapixel camera that can capture 6 full moons’ worth of sky in a single image. Planet Nine's aphelion should be somewhere between the constellations Orion and Taurus, making the search area visible from September through February of every year. Subaru should be able to cover the search area in about 20 nights. That may not seem like a lot of time, but astronomers using Subaru to search for Planet Nine have to compete with other astronomers for time on the telescope. Not only that but, bad weather interfered with the first two years of Planet Nine searching, so only a fraction of the search area has been covered to date. At this rate, it'll probably take a few more years before the entire Planet Nine search area is completely covered. .
Luckily, a second team of astronomers led by Scott Sheppard from Carnegie Science are also using Subaru to conduct their own search for Planet Nine. Even better, Sheppard’s team are also piggybacking on another survey with another telescope. The Dark Energy Survey uses the 4-meter Victor Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile.
 |
| Victor Blanco Telescope Source: wikipedia user David walker / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/) |
The telescope used the Dark Energy Camera, or DE Cam mounted at the telescope's prime focus. DE Cam’s field of view is twice the Hyper Supreme-Cam mounted on the Subaru telescope. But its detector is 300 megapixels smaller and it's mounted to a telescope that is half the size of Subaru. Even so, Sheppard and his team used the Blanco telescope to discover several new trans-Neptunian objects that are even fainter than Planet Nine is predicted to be. So this tells us that the search for Planet Nine is in fact possible. And by the way, these objects all follow orbits that are clustered in a manner that is consistent with Planet Nine.
Now you may be wondering how is it they keep finding these tiny objects when there's supposedly a giant planet they haven't found yet?
Well the answer is we expect there to be thousands, maybe even hundreds of thousands of these tiny objects, but only one giant planet. It's like going fishing in the ocean - you expect to catch a lot of small fish, but you don't expect to catch a whale. But what if neither the Subaru nor Blanco telescopes find Planet Nine? That would be unfortunate, but it wouldn’t necessarily rule out the planet's existence. It could mean it's simply on a different part of its orbit, so a different region of the sky would need to be searched. Or it could be that Planet Nine is on a much larger orbit than predicted, and its aphelion would carry it farther away, making it too faint to be detected by Subaru. But there is another possibility which kind gives us the screaming heebie-jeebies. Planet Nine could be passing in front of the Milky Way, lost in the glare of a crowded field of bright background stars. Fortunately, there’s a telescope under construction that should be able to resolve Planet Nine even among such a crowded field. The Large Synoptic Survey Telescope will make the widest and deepest scan of the southern sky over the course of a decade.
 |
| Large Synoptic Survey Telescope Source: LSST Project Office / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0) |
LSST will be armed with an 8.4 meter mirror, and a gigantic, 3 Gigapixel camera with a 9.6 square degree field of view. That will give LSST the sensitivity and clarity to distinguish Planet Nine even if it’s fainter than expected, and even if it’s passing across the Milky Way. Not only that, but LSST will complete a full scan of the entire sky once every five to seven days and repeat over and over again for a decade. That means that every point in the sky will be imaged by LSST more than 800 times. This means that if Planet Nine is on a completely different orbit, or if it's farther and fainter than expected, LSST should be able to detect it as long as it's somewhere in the southern sky. Meanwhile, the search for Planet Nine continues. It's November 2018, and Mike Brown and his team have time scheduled on Subaru in December. This will mark the third year searching for Planet Nine, and hopefully a little bit more of the sky will be covered. But each year brings new discoveries of distant objects in the outer solar system, each of which seem to be pointing the way to Planet Nine. There are so many new worlds waiting to be discovered, both right here in our solar system and far beyond. that's all thank you.
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