- 3083 - EXOPLANETS - recent planet discoveries? Astronomers have confirmed the discovery of a “planetoid” that is almost four times farther from the Sun than Pluto, making it the most distant object ever observed in our solar system.
------------------- 3083 - EXOPLANETS - recent planet discoveries?
- The planetoid, nicknamed "Farfarout," was first detected in 2018, and the team has now collected enough observations to pin down the orbit. It has a designation of “2018 AG37“.
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- Farfarout's name distinguished it from the previous record holder "Farout," found by the same team of astronomers in 2018. Farfarout's current distance from the Sun is 132 astronomical units (au); 1 au is the distance between the Earth and Sun.
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- For comparison, Pluto is only 34 au from the Sun. The newly discovered object has a very elongated orbit that takes it out to 175 au at its most distant, and inside the orbit of Neptune, to around 27 au, when it is closest to the Sun.
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- Farfarout's journey around the Sun takes a thousand years, crossing the giant planet Neptune's orbit every time. This means Farfarout has probably experienced strong gravitational interactions with Neptune over the age of the solar system, and is the reason why it has such a large and elongated orbit.
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- Because of this long orbital period, it moves very slowly across the sky, requiring several years of observations to precisely determine its trajectory.
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- Farfarout will be given an official name after its orbit is better determined over the next few years. It was discovered at the Subaru 8-meter telescope located atop Maunakea in Hawaii, and rediscovered using the Gemini North and Magellan telescopes in the past few years to determine its orbit based on its slow motion across the sky.
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- Farfarout is very faint, and based on its brightness and distance from the Sun, the estimated size is about 400 km across, putting it on the low end of being a dwarf planet, assuming it is an ice-rich object.
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- The discovery of Farfarout shows our increasing ability to map the outer solar system and observe farther and farther towards the fringes of our solar system. Only with the advancements in the last few years of large digital cameras on very large telescopes has it been possible to efficiently discover very distant objects like Farfarout.
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- Even though some of these distant objects are quite large, being dwarf planet in size, they are very faint because of their extreme distances from the Sun. Farfarout is just the tip of the iceberg of solar system objects in the very distant solar system yet to be discovered.
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- Because Neptune strongly interacts with Farfarout, its orbit and movement cannot be used to determine if there is another unknown massive planet in the very distant solar system, since these interactions dominate Farfarout's orbital dynamics.
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- Only those objects whose orbits stay in the very distant solar system, well beyond Neptune's gravitational influence, can be used to probe for signs of an unknown massive planet. These include “Sedna” and “2012 VP113“, which, although they are currently closer to the Sun than Farfarout (at around 80 au), they never approach Neptune and thus would be most influenced by the possible ‘Planet X” instead.
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- Farfarout's orbital dynamics can help us understand how Neptune formed and evolved, as Farfarout was likely thrown into the outer solar system by getting too close to Neptune in the distant past. Farfarout will likely interact with Neptune again since their orbits continue to intersect.
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- Mini-Neptunes and super-Earths up to four times the size of our own are the most common exoplanets orbiting stars beyond our solar system.
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- Until now, super-Earths were thought to be the rocky cores of mini-Neptunes whose gassy atmospheres were blown away. A new study shows that some of these exoplanets never had gaseous atmospheres to begin with, shedding new light on their mysterious origins.
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- From observations, we know about 30 to 50 percent of host stars have one or the other, and the two populations appear in about equal proportion. But where did they come from?
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- One theory is that most exoplanets are born as mini-Neptunes but some are stripped of their gas shells by radiation from host stars, leaving behind only a dense, rocky core. This theory predicts that our Galaxy has very few Earth-sized and smaller exoplanets known as Earths and mini-Earths.
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- Astronomers estimate that there is roughly one exoplanet per star in our galaxy. Of course, some stars have many planets, our own sun has eight. And some stars have none. But if a star lives long enough, forming planets seems to be the rule, rather than the exception.
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- So, that means the Milky Way should contain around 100 thousand million exoplanets. The running counter of known exoplanets, as of March, 2021, stands at 4,108 confirmed targets.
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- But astronomers are surprisingly good at figuring out what they can’t see. They know that their telescopes aren’t powerful or precise enough to see the stealthiest planets, those that are very small, very far from their stars, or around stars very far from Earth. And conversely, there are regions of space where astronomers are pretty confident they’ve found all the planets within a certain range.
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- By combining the knowledge of what they can see, the known exoplanets, with the knowledge of what they can’t see, the parts of space currently beyond our ability to investigate, astronomers end up at the approximation of one planet per star.
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- The findings suggest that not all super-Earths are remnants of mini-Neptunes. Rather, the exoplanets were formed by a single distribution of rocks, born in a spinning disk of gas and dust around host stars. Some of the rocks grew gas shells, while others emerged and remained rocky super-Earths.
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- Planets are thought to form in a spinning disk of gas and dust around stars. Rocks larger than the moon have enough gravitational pull to attract surrounding gas to form a shell around its core. Over time this shell of gas cools down and shrinks, creating space for more surrounding gas to be pulled in, and causing the exoplanet to grow.
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- Once the entire shell cools down to the same temperature as the surrounding nebular gas, the shell can no longer shrink and growth stops.
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- For smaller cores, this shell is tiny, so they remain rocky exoplanets. The distinction between super-Earths and mini-Neptunes comes about from the ability of these rocks to grow and retain gas shells.
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- These explain the origin of the two populations of exoplanets. The theory could help decipher how common rocky exoplanets like Earths and mini-Earths may exist. Maybe they are looking back at us and trying to figure out the same thing?
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March 8, 2021 EXOPLANETS - recent planet discoveries? 3083
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