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What is hiding in the outer solar system?



In 1992, the discovery of a small object revealed a great mystery: that the solar system was far larger than we had ever imagined. Previously, we had just confirmed the existence of a lonely, strange, cold Pluto in a region called Kuiper Belt. The Kuiper Belt is a cluster of icy objects located in an area outside Neptune's orbit – like a colder, wetter asteroid belt. Until 1992, it was strictly theoretical because no one except Pluto had observed anything. The discovery of 1992 QB1 marked only the second time that an object was found in the Kuiper Belt. In the next few years, discoveries of these small, cold worlds were found between 1992 and 1

999 – 80+, and today hundreds are known. With the outer solar system studies on the Mauna Kea and La Palma Observatories in the 1990s, we have finally begun to tap the "third zone" of the solar system as something more than just theoretical.

Now that our understanding of the outer solar system has grown, we are faced with new questions. And it renews discussions about planets behind Neptune. And not Pluto, Eris, Makemake, or the other fascinating and dynamic dwarf planets we've already identified – but undiscovered objects that may be Mars-sized or larger.

Planet Nine

In some cases, these dwarf planets may also be pointing the way to bigger things – like previously undiscovered planets. In 2003, astronomers Mike Brown, Chad Trujillo and David Rabinowitz announced the discovery of Sedna. Sedna's orbit appeared to extend to 970 times the Sun-Earth distance (known as an astronomical unit or AU) before approaching 76 AU again. It is expected that Sedna's entire orbit around the Sun will take 11,000 years.

Sedna seemed strange. But the discovery of 2012 VP113 began to complicate things. This property, which was announced in 2014, was even further than Sedna. But it had many similarities – it also had a long, strange orbit that was inclined over the plane of the solar system. And there were other objects like these, a group whose approach to the sun was no closer than 30 AU and whose extreme point was 250 AU.

"The discovery of these ETNOs shows that this remote part of the solar system is far from empty and the characteristics of its inhabitants are sometimes quite puzzling," says Carlos de la Fuente Marcos of the Universidad Complutense de Madrid.

This led astronomers Mike Brown and Konstantin Batygin to an unusual conclusion: The eccentric and off – aircraft lanes of these objects were not coincidental, but paths that were carefully united by avoiding an even larger object. And this object is a cold, distant planet, named in 2015 in the newspaper "Planet Nine" and announcing its prediction. Planet Nine itself probably began near the sun, but migrated to the farther reaches of the solar system, which turned its course around the sun.

The planet would have an oblong orbit leading it around the Sun and approaching our star as close as 200 AU at its closest point and up to 1,200 AU at the farthest point. The entire trip would take an estimated 10,000 to 20,000 years. When it's outside, it should be bright enough to reflect some of the sun's light, making it visible to telescopes here on Earth. The only catch-it moves so slowly that it can take some time to distinguish it from background stars.

The idea is that Planet Nine originated along with the other eight known planets and then migrated as Jupiter to the outer solar system and Saturn gradually destabilized its orbit. When Planet Nine took off, it dumped much of the icy body in the Kuiper Belt, leaving behind bodies like Sedna, which have since been called "extreme trans-Neptune objects." "They are like a cake that is cut out a piece and then throw out the rest of the cake," says Batygin, a professor at Caltech. The "rest of the cake" – a huge chunk of icy worlds ranging in size from small comets to mid-sized rocky planets on the edge of the Kuiper Belt – was probably whipped out of the Solar System. Overall, 75 percent of the mass of the outer Kuiper belt was lost.

Batygin and Brown say they have a 99 percent certainty that Planet Nine is out there. Their confidence that Planet Nine exists depends on these approximately 10 extreme trans-Neptunian objects. More are yet to be found – the last discovery was announced just last week. Named BP519, it has a sedna-like orbit. Planet Nine is expected to be about 10 times the size of the Earth and probably the largest undiscovered object yet. Its predicted orbit and our understanding of the motions of planets, dwarf planets, asteroids, and comets within our solar system make it unlikely that any other hidden ice giants lurk within those outer limits. "I think, in a sense, [Planet Nine] can be thought of as the last major object in the solar system," says Batygin.

Infrared studies have certainly excluded Jupiter or Saturn. But there might be other planet-sized objects out there, just nothing big. "You can still have Earth and Mars objects, but the solar system is actually going out of the property," says Batygin.

Dark Mars

Last year, Kat Volk, a professor at the University of Arizona, was the lead author of an article in the Astrophysical Journal in which another undiscovered planet was theorized. She also looked at the Kuiper Belt population, looking for strange orbits and digging out more than a few. Volk says that the paper was inspired in part by the news of Planet Nine, and was an opportunity to search for other objects of considerable weight by looking at the orbital dynamics of the Kuiper Belt.

"We saw that the inner part of the Kuiper Belt's inner part looked really good, it matched the plane of the other objects," she says.

But the farther she went, the stranger they became. While most of the Solar System exists along a plane that extends outward from the Sun, with few deviations of more than a few degrees, these outer objects of the Kuiper Belt had unduly high deviations. These deviants pointed to a hidden disturber: a Mars planet about 100 AU from the Sun. Like Planet Nine, it would move slowly, but still be able to reflect the light of the sun.

"We estimated how bright the thing would be, and it would be really bright, so you do not need anything extra." [to find it] People say: A sky survey such as the Large Synoptic Survey Telescope could help find nocturnal images of the sky and to search for slow-moving objects.

In addition, there have been some papers suggesting other planets in recent years.An article in the Monthly Reports of the Royal Astronomical Society of 2014 suggested that at least two other planets more massive than One of these authors, de la Fuente Marcos, later reworked it into an object that behaved much like Planet Nine, but is closer to the Sun. Another article, The Remote Super Earth proposed to 4000 AU based on a radio signal, was quickly withdrawn, as other astronomers in the community the apparent impossibility saw the claimed size and parameters of the object. Simply put, if the Atacama Large Millimeter Submillimeter Array could randomly capture such an object with a narrow field of view, then we should see more objects like this out there – far more mass than we believe our solar system ever contained. And alternate explanations for the odd orbits of Sedna and his ilk are abound – including large planets with alternating orbital configurations with Planet Nine.

People say that while they are fairly neutral on Planet Nine's existence, "it does generate new ideas about what dynamics we should think about." A better understanding of the outer solar system will likely lead to new surprises – and in the next few years, studies such as LSST and giant telescopes such as the 30-meter telescope and the James Webb Space Telescope may not be carried out. I only find Planet Nine, but Planet Ten or even Planet Eleven. It may be about calculating the correct location and directing a telescope there, similar to the discovery of Neptune 1847 by Johann Galle (or John Couch Adams, whoever you ask) based on predictions from Urbain Le Verrier, or perhaps Also be there if you move something subtle from night to night in a sky survey. Simply put, there is a lot to find out there.

"There are a lot of things we did not find in the Kuiper belt," says Volk. "It's not like the asteroid belt where we know all the big objects, we can not even rule out Neptune-sized things in the really distant solar system."


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