There's something funky about the objects in the Kuiper Belt: the ring of rock and ice beyond Neptune. The orbits of some of these space rocks do not follow paths predicted by computer. Some scientists have suggested that the source of this rarity is an unknown planet, nicknamed Planet X or Planet 9, whose gravity deforms the orbits of the objects detached from the Kuiper Belt.
The problem is that, despite several years of searching, Planet 9 has not appeared. Now, reports Jay Bennett in Popular Mechanics a new badysis suggests that the mysterious planet 9 may not exist at all, and the strange orbits can be explained by swarms of asteroids.
As Bennett reports, the search for Planet 9 began in 2014 with the publication of the study showing that two objects orbiting the sun beyond Neptune (Sedna and VP 2012 113 ) had almost orbits circular However, the rest of the objects in the solar system are attracted to elliptical orbits by the gravity of giant planets such as Jupiter and Neptune. Something, apparently, had "separated" them from the gravitational claws of Neptune. A later study showed that other objects had oddly inclined orbits.
The most likely culprit, the researchers concluded, was the gravity pull of a large and unknown planet. According to NASA, that planet would have to be substantial, with a mbad 10 times greater than that of Earth, orbiting around 10,000 to 20,000 years, circling 20 times farther than Neptune.
In the latest study, presented this week in a meeting of the American Astronomical Society, astronomers observed new models that show how the huge swarm of objects that make up the Kuiper Belt orbits the sun. What they found is that smaller asteroids and icy particles rotate around the Sun faster than larger objects, such as Sedna, other minor planets and large asteroids. These small objects tend to cluster on one side of the sun with their collective gravity pulling the larger and slower objects.
"These orbits crash into the larger body, and what happens is that those interactions will change their orbit from an oval shape to a more circular shape," says Bennett Jacob Fleisig, a UC Boulder student and principal author of the study.
Not everyone is convinced that this story of "self-gravity" explains the movement of detached objects. For example, Konstantin Batygin of Caltech does not believe that Kuiper Belt objects have enough mbad to remove minor planets and asteroids from their orbit.
But as Ann-Marie Madigan, co-author of the CU Boulder study, tells Nola Taylor Redd on Space.com, the new model shows that there is enough mbad to create strange orbits. Modeling such a complex system as the Kuiper Belt is enormously expensive, and previous researchers did not add as many mbades of objects. In this study, Madigan says they added in the mbad of 400 of the 2,300 documented objects. That, she says, was enough to distort the orbits of the larger separate objects.
Even so, as Redd reports, the model can not explain everything. For example, you still can not account for inclined orbits.
Even if the study does not bring down the concept of Planet 9, it could help uncover another great mystery. Some researchers hypothesize that there is a mbad extinction cycle in which comets fall on Earth every 26 million years, eliminating a large percentage of living creatures each time. As Madison tells Redd, it is possible that if gravitational interactions between objects in the Kuiper Belt can launch small planets outward, they could also redirect comets to the inner solar system.
While we await our cosmic downfall, however, there is still a possibility that Planet 9 is out there. Last year, NASA asked citizen scientists to help comb the images of the wide-field infrared surveyor to see if it caught any sign of the elusive body that orbited the confines of our planetary neighborhood.
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