Research focuses on unknown planet

Scientists believe there is evidence of another planet.
Scientists believe there is evidence of another planet.
Heather Roper, Lunar and Planetary Laboratory
Researchers believe there is evidence of another unseen planet in a distant swath of the solar system.

     Scientists are making these assertions based not on spotting the planet in the sky, but on studying the movement of neighboring objects in the Kuiper Belt, a vast area of the solar system beyond Neptune.
     While a similar announcement was made last year about a theoretical planet nine, researchers say this is different. Planet nine is thought to have a mass about 10 times that of Earth. This new report involves the possibility of a separate, smaller planet with a mass somewhere between that of Mars and Earth, according to a news release from the University of Arizona.
     Kuiper Belt objects are debris left over from the formation of the solar system. Most of these objects orbit the sun with “orbital tilts (inclinations) that average out to what planetary scientists call the invariable plane of the solar system,” the university’s news release explains. But “the most distant of the Kuiper Belt's objects do not. Their average plane … is tilted away from the invariable plane by about eight degrees. In other words, something unknown is warping the average orbital plane of the outer solar system.”
     The researchers, Kat Volk, a postdoctoral fellow, and Renu Malhotra, professor of planetary sciences at the University of Arizona's Lunar and Planetary Laboratory, analyzed the tilt angles of the orbital planes of more than 600 objects in the Kuiper Belt, focusing on the change or “wobble” in orientation of various objects.  
     They calculated that an unknown planet would be roughly 60 astronomical units from the sun. (An astronomical unit is defined by NASA as “the average distance between the Earth and the sun, about 150 billion meters.”) Planet nine is believed to be much farther out--500 to 700 astronomical unites from the sun.
      The research is to be published in the Astronomical Journal.


     Scientists find evidence of "Planet Nine"

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