On January 20th, 2016 we learned about

Objects’ orbits pushed and pulled by possible ninth planet

Beyond the dwarf planet Pluto are a variety of small, cosmic objects, and quite possibly at least one big one. While some of these smaller frozen rocks in what’s known as the Kuiper Belt have been directly identified, many were behaving a bit oddly when observed by astronomers. Their orbits included odd wobbling off their expected course, indicating that something was pulling on them from deeper in space. This kind of wobbling motion has often been tied to the presence of a large body like a planet, but researchers didn’t want to assume that that was the case too early.

Researchers at Caltech started modeling different possibilities to see which possible scenarios best matched observed data. They needed something that could cause at least six Kuiper Belt objects to not only wobble, but wobble in the same place, despite their orbits not being perfectly aligned otherwise. Furthermore, something was causing their orbits to tilt at the same angle in relation to other planets’ orbits, which narrowed the possible explanations considerably. There was very likely something significant at the edge of the known solar system, as these behaviors only had a 0.007 percent chance occurring randomly.

Medium planet, massive orbit

Even with the possible excitement of a new planet looming in their imaginations, the team still needed to rule out other possible explanations. A cluster of smaller objects was unlikely because of the size that would be necessary to make such firm gravitational tugs on the observed Kuiper objects. Even the first simulation of an actual planet didn’t hold up, as a planet simply moving around the affected objects would create the wobbling they had seen.The best match was then a medium-sized planet with an inverted orbit— basically moving around the sun in an opposite orientation from its neighbors, spending much of its year out on its own end of the solar system. This large orbit would give the new planet a 20,000 year trip around the sun, sometimes moving as far as 56 billion miles away from the sun. Yet even as a distant, “loner” planet, the simulated object could influence other Kuiper Belt residents during their relatively brief encounters.

Normalizing our solar system

In the end, this potential ninth planet wouldn’t be as odd as all this may sound. The simulated gas planet actually fits well not only with the original orbital wobbles, but also with observed behavior of other objects, like Sedna. The new planet would also but our solar system more in line with other systems astronomers have studied, which usually have more medium-sized gas planets than we have near Earth. More data is obviously needed to confirm all this, some of which may be a long time coming if Planet Nine is currently vacationing at the end of its enormous orbit.

Source: Caltech Researchers Find Evidence of a Real Ninth Planet by Kimm Fesenmaier, Caltech News

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