According to NASA, WISE has two coolant tanks that keep the spacecraft's normal operating temperature at 12 Kelvin (minus 438 degrees Fahrenheit). The outer, secondary tank is now depleted, causing the temperature to increase. One of WISE's infrared detectors, the longest-wavelength band most sensitive to heat, stopped producing useful data once the telescope warmed to 31 Kelvin (minus 404 degrees Fahrenheit). The primary tank still has a healthy supply of coolant, and data quality from the remaining infrared detectors remains high. NASA stated.
WISE's infrared telescope and detectors are kept chilled inside a Thermos-like tank of solid hydrogen, called a cryostat. This prevents WISE from picking up the heat, or infrared, signature of its own instrument. The solid hydrogen, called a cryogen, was expected to last about 10 months -- the mission launched in December 2009.
WISE observes infrared light, letting it show the darkest components of the near-Earth object population -- those that don't reflect much visible light. Visible-light estimates of an asteroid's size can be deceiving, because a small, light-colored space rock can look the same as a big, dark one. In infrared, however, a big dark rock will give off more of a thermal or infrared glow, and reveal its true size, NASA stated.
NASA said WISE completed its primary mission, a full scan of the entire sky in infrared light, on July 17, 2010. The mission has taken more than 1.5 million snapshots so far, uncovering hundreds of millions of objects, including asteroids, stars and galaxies. It has discovered more than 29,000 new asteroids to date, more than 100 near-Earth objects and 15 comets, NASA said.
For now WISE is performing a second survey of about one-half the sky. It's possible the remaining coolant will run out before that scan is finished. Scientists say the second scan will help identify new and nearby objects, as well as those that have changed in brightness. It could also help to confirm oddball objects picked up in the first scan, NASA stated. Data from the mission will be released to the astronomical community in two stages: a preliminary release will take place six months after the end of the survey, or about 16 months after launch, and a final release is scheduled for 17 months after the end of the survey, or about 27 months after launch, NASA stated.
Almost as soon as it came online in December, WISE spotted a new, half-mile wide asteroid some 98 million miles from Earth. The near-Earth object, designated 2010 AB78 and circles the Sun in an elliptical orbit tilted to the plane of our solar system. The object comes as close to the Sun as Earth, but because of its tilted orbit, it will not pass very close to Earth for many centuries. This asteroid does not pose any foreseeable impact threat to Earth, but scientists will continue to monitor it.
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