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A NASA spacecraft has pounded another nail into the coffin of the hypothetical solar system body called "Planet X" or "Nemesis."
Some astronomers have proposed the existence of an undiscovered planet or other large body in the outer reaches of the solar system, based on their analysis of changes in the orbits of far-out comets. But after scanning the entire sky, the space agency's Wide-Field Infrared Survey Explorer, known as WISE, found no signs of such objects.
The probe did, however, find several thousand new objects much farther out. The discoveries — and non-discoveries — are described in two research papers published in the Astrophysical Journal. [Images from NASA's WISE Space Telescope]
WISE scanned the sky throughout 2010 and in early 2011, with a six-month gap between the two observations. By comparing the two sets of infrared images, astronomers could identify objects that had moved slightly across the sky. WISE imaged nearly 750 million stars, asteroids and galaxies, some of which had never been spotted before.
One study, led by Kevin Luhman of Penn State University, found 762 new objects among the data, but no signs of a Saturn-sized object out to 10,000 times the Earth-sun distance, or 10,000 astronomical units. Nor did Luhman spot any Jupiter-size or larger objects out to 26,000 AU.
A second study, led by Davy Kirkpatrick of NASA's Infrared and Processing Analysis Center at the California Institute of Technology, discovered 3,525 new stars and brown dwarfs, some of which overlapped Luhman's finds. Brown dwarfs are objects that are larger than planets but too small to sustain fusion in their core as true stars do.
One of the newfound stars is located just 20 light-years away in the constellation Norma.