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Planet X / Planet Nine
An artist’s conception shows Planet X, a.k.a. Planet Nine. (Credit: Robin Dienel / Carnegie Inst.)

The hypothetical world known as Planet X or Planet Nine hasn’t yet been found, but thanks to the search, astronomers have discovered smaller worlds on the solar system’s edge.

Mapping such objects could lead to the big discovery: a planet that’s thought to be at least several times bigger than Earth, lurking at least 200 times farther away from the sun. Or it could lead to a different explanation for the puzzling, highly elongated orbits of some of the objects that lie far beyond Pluto.

Planet Nine’s existence was proposed last year as the most elegant way to account for the orbits of worlds such as Sedna and 2012 VP113 (which has been nicknamed “Biden” in honor of the veep). Ever since then, astronomers have been surveying the skies in hopes of tracking it down.

Among those astronomers are Scott Sheppard of the Carnegie Institution for Science and Chad Trujillo of Northern Arizona University. They were on the discovery team for 2012 VP113. Now they’re part of a team conducting a survey using instruments such as the Dark Energy Camera on the NOAO 4-meter Blanco telescope in Chile and the Japanese Hyper Suprime Camera on the 8-meter Subaru telescope in Hawaii.

So far the survey has covered nearly 10 percent of the sky.

Sheppard and Trujillo identified several previously unknown objects and have submitted their coordinates to the International Astronomical Union’s Minor Planet Center for official designations. A paper on the discoveries has been accepted for publication in the Astronomical Journal.

The list includes these mini-worlds:

  • 2014 SR349, which is in the kind of extreme orbit that could hypothetically have been perturbed by Planet Nine.
  • 2013 FT28, which isn’t quite as much in the sweet spot for Planet Nine action, dynamically speaking.
  • 2014 FE72, which is said to be the first identified object from the faraway Oort Cloud with an orbit entirely beyond Neptune. The orbit is stretched out far enough to take it more than 3,000 times farther away from the sun than Earth is. The astronomers say its orbital path seems likely to be influenced by gravitational forces beyond the solar system, such as passing stars or the galactic tide.

The orbits that have been mapped so far aren’t sufficient to solve the planetary mystery. Planet Nine may be so dim and so far away that it’ll remain hidden until next-generation telescopes come into play. And there’s still the possibility that it doesn’t exist, which means some other phenomenon would have to explain the weird orbits of objects like Sedna, 2012 VP113 and 2014 SR349.

“Right now we are dealing with very low-number statistics, so we don’t really understand what is happening in the outer solar system,” Sheppard said in a news release. “Greater numbers of extreme trans-Neptunian objects must be found to fully determine the structure of our outer solar system.”

Even if Planet Nine isn’t found, the search should shed further light on the farther reaches of the solar system. And that, figuratively speaking, is truly far out.

Far-out orbits
This diagram highlights the orbits of three newfound worlds, plus a potential orbit for the yet-to-be-discovered object known as Planet X or Planet Nine. Click on the image for a larger version. (Credit: Robin Dienel / Carnegie Institution)
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