WISE Satellite finds no evidence for Planet X in survey of the sky

WISE Chart — This chart shows what types of objects WISE can and cannot see at certain distances from our sun. Bodies with larger masses are brighter, and therefore can be seen at greater distances. For example, if a Jupiter-mass planet existed at 10,000 au, WISE would have easily seen it. But WISE would not have been able to see a Jupiter-mass planet residing at 100,000 au -- it would have been too faint. Credit: Janella Williams, Penn State University. Credit: Penn State. Creative Commons

After searching hundreds of millions of objects across the sky, NASA's Wide-Field Infrared Survey Explorer (WISE) has turned up no evidence of the hypothesized celestial body in our solar system commonly called "Planet X," according to published scientific papers including a new study in The Astrophysical Journal authored by Kevin Luhman of the Center for Exoplanets and Habitable Worlds at Penn State University. "The outer solar system probably does not contain a large gas-giant planet, or a small companion star," said Luhman, who is an associate professor of astronomy and astrophysics at Penn State.

Researchers previously had theorized about the existence of a large, but unseen, celestial body suspected to exist somewhere beyond the orbit of Pluto. In addition to "Planet X," the body had other nicknames, including "Nemesis" and "Tyche." Luhman's recent study, which involved an examination of WISE data covering the entire sky in infrared light, 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. One astronomical unit equals 93 million miles. Earth's distance from the Sun is 1 au, and Pluto's is about 40 au.

But searches of the WISE data are not coming up empty. They reveal several thousand new stars and cool bodies called brown dwarfs that are in our Sun's "backyard" but outside our solar system. "Neighboring star systems that have been hiding in plain sight just jump out in the WISE data," said Ned Wright of the University of California, Los Angeles, the principal investigator of the WISE mission.

Another WISE paper published in The Astrophysical Journal, which concentrated on objects beyond our solar system, found 3,525 stars and brown dwarfs within 500 light-years of our Sun. "We're finding objects that were totally overlooked before," said Davy Kirkpatrick of NASA's Infrared and Processing Analysis Center at the California Institute of Technology. Kirkpatrick is lead author of this second paper. Some of these 3,525 objects also were found in Luhman's study, which catalogued 762 objects.

The WISE mission operated from 2010 through early 2011, during which time it performed two full scans of the sky -- with a six-month gap between. The survey captured images of nearly 750 million asteroids, stars, and galaxies. In November 2013, NASA released data from the AllWISE program, which now enables astronomers to compare the two full-sky surveys to look for moving objects.

In general, the more an object in the WISE images appears to move over time, the closer it is to Earth. This visual clue is the same effect at work when one observes a plane flying low to the ground versus the same plane flying at higher altitude. Though traveling at the same speed, the plane at higher altitude will appear to be moving slower.

Searches of the WISE data catalog for these moving objects are uncovering some of the closest stars. The discoveries include a star located about 20 light-years away in the constellation Norma and a pair of brown dwarfs -- reported in March 2013 to be only 6.5 light-years away -- making it the closest star system to be discovered in nearly a century.

The star system moving — The WISE J104915.57-531906 star system was discovered through its rapid motion across the sky, which is shown in these images taken between 1978 and 2010 by the Digitized Sky Survey, the Two Micron All-Sky Survey and the WISE satellite. Credit: NASA/STScI/JPL/IPAC/University of Massachusetts. All Rights Reserved.

Despite the large number of new solar neighbors found by WISE, "Planet X" did not show up. Previous speculations about this hypothesized body stemmed, in part, from geological studies that suggested a regular timing associated with mass extinctions on Earth. The idea was that a large planet or small star hidden in the farthest reaches of our solar system might periodically sweep through bands of outer comets, sending them flying toward our planet. The mass-extinction theories largely were ruled out due to lack of evidence, even prior to the new WISE study. Other theories based on irregular comet orbits also had postulated a Planet X-type body. Luhman's new WISE study now argues against these theories, as well.

Both of the WISE searches were able to find objects the other one missed, suggesting many other celestial bodies likely await discovery in the WISE data. "We think there are even more stars out there left to find with WISE. We don't know our own Sun's backyard as well as you might think," said Wright.

The Center for Exoplanets and Habitable Worlds is supported by Penn State University, the Penn State Eberly College of Science, and the Pennsylvania Space Grant Consortium

More information on WISE, and its latest adaptation, the asteroid-hunting mission NEOWISE, is online at http://www.nasa.gov/wise.