Just two days ago a reader asked whether NASA’s Wide-field Infrared Survey Explorer (WISE) had found any sign of a hypothesized companion to the sun dubbed “Planet X” also known as “Nemesis”, “Tyche” and “Nibiru”. After searching through hundreds of millions of images and turning up no sign of the object, it looks like we can finally put the idea to bed.
WISE swept the sky once in 2010 and again in early 2011. Objects close to us appear to move faster than distant objects when viewed over time. Nearby stars appear to move more quickly across the sky than distant ones much like a low-flying plane appears to zoom by compared to the same plane flying at high altitude.
By comparing images taken by WISE six months apart, astronomers have found thousands of stars and brown dwarfs in our sun’s “backyard” by flagging those moving fastest.
All told, WISE turned up 3,525 stars and brown dwarfs within 500 light-years of our sun, objects totally overlooked or unseen by ground-based optical telescopes. Take the pair of brown dwarfs hidden practically under our noses only 6.5 light years away. Called WISE J104915.57-531906, it’s the third closest star system to Earth and the closest discovered since astronomer E.E. Barnard spotted “Barnard’s Star” in 1916 nearly a hundred years ago.
But WISE’s two complete infrared sweeps of the sky found that no object the size of Saturn or larger exists out to a distance of 10,000 astronomical units (AU), and no object larger than Jupiter exists out to 26,000 AU or 2.4 trillion miles. One astronomical unit equals 93 million miles or Earth’s distance from the sun. Dwarf planet Pluto orbits about 40 AU from the sun.
“The outer solar system probably does not contain a large gas giant planet, or a small, companion star,” said Kevin Luhman of the Center for Exoplanets and Habitable Worlds at Penn State University, University Park, Pa., author of a paper in the Astrophysical Journal describing the results.
Meanwhile, astronomers have been sifting through the reams of WISE data since the probe wrapped up its mission in 2011. In addition to the new stars mentioned, the orbiting spacecraft captured photos of nearly 750 million asteroids, stars and galaxies. Since scientists continue to pour over the data, there’s a remote chance a Planet X might be found, but much more likely we’ll continue to find other stars never seen before in regular optical telescopes.