After finishing its original mission, WISE actually got a trial run of sorts on what eventually would become its second act. After NASA shut down much of its infrared equipment when the coolant began to run down, scientists utilized what was still operating to work on a project called NEOWISE between January 2010 and February 2011. The spacecraft began scanning the sky for closer objects. During 2010, it observed about 158,000 rocky bodies, including 34,000 asteroids in the solar system's main belt between Mars and Jupiter, and spotted 135 potentially hazardous near-Earth objects — that is, ones close enough to Earth's orbit that they might present a collision hazard [source: NASA].
When NASA reactivates WISE again, it will use the satellite's 16-inch (40-centimeter) telescope and its infrared sensors to look for additional near-Earth objects. Because the sensors no longer are being super-cooled, they don't all work, and thus the satellite isn't as good at detecting radiation from distant, faint objects as it once was. But it still has enough capability left to spot infrared radiation from nearer objects. "Two of our four infrared detectors still work even at warmer temperatures, so we can use those bands to continue our hunt for asteroids and comets," Amy Mainzer of NASA's Jet Propulsion Laboratory told Space.com in October 2010 [source: Malik].
Infrared sensing is a particularly useful tool, not only for spotting asteroids but for accurately calculating their size. Asteroids reflect light but don't emit it, and they vary in albedo, or the ability to reflect visible light. That means that to a regular optical telescope, a small, light-colored space rock can look as big as a much larger dark one. An infrared telescope, however, picks up a part of the non-visible spectrum that a regular telescope misses, and can give a more complete picture of an asteroid [source: NASA].
Scientists are betting that capacity will enable WISE to give us a better idea of which asteroids are big enough and close enough to be a problem — and which might be the right size to be captured by a robotic spacecraft.