LOS ANGELES — The space-based telescope known as WISE has been orbiting Earth in a hibernative state for the past 2½ years. But now, nap time is over.
WISE has some asteroid hunting to do.
This week, NASA announced it will reactivate the sleeping space telescope and put it back to work as an asteroid hunter, focused on finding potentially hazardous asteroids and other space rocks that could come uncomfortably close to Earth.
NASA hopes the sleeping infrared telescope still has enough juice in it to discover 150 previously unknown near-Earth objects, and to help scientists learn more about the shape and size of 2,000 others, the agency said in a statement.
It may even help the agency find the perfect asteroid to capture and land a spacecraft on, later this decade.
WISE, the Wide-field Infrared Survey Explorer, was launched in December 2009, tasked with scanning the night sky in infrared light - looking for heat emanating from galaxies, stars and asteroids.
By the time its primary mission ended in February 2011, WISE had captured more than 2.7 million images in multiple wavelengths and cataloged more than 560 million objects in space, according to NASA.
In a separate mission, dubbed NEOWISE, the telescope also made the most accurate survey of near-Earth objects to date.
When the mission was over, the scientists decided to put it to sleep, rather than turn it off completely.
"We turned off the cameras, and all the unnecessary electronics, and what was left was basically enough power to keep its solar arrays pointing toward the sun so it can still get power," said Amy Mainzer, principal investigator for NEOWISE at the Jet Propulsion Laboratory.
Waking up the telescope and getting it back into working mode shouldn't be too hard, said Mainzer, but the first step is to cool it down.
"The temperatures have warmed up to about 200 degrees above absolute zero, which sounds cool to us on Earth, but is actually quite warm for an infrared telescope," she said.
Because all the telescope's refrigerants are long gone, the team plans to cool WISE off by having it stare off into deep space for a bit.
"When it looks at the cold background of deep space, most of the heat will radiate away," Mainzer said.
Once the telescope is down to 75 degrees above absolute zero, Mainzer and her team will recalibrate its instruments. She said only two of the telescope's four channels can operate without refrigerants.
Although WISE was not originally designed to be an asteroid hunter, Mainzer said its infrared sensors that measure heat make it especially good at finding and characterizing space rocks.
Telescopes that rely on light sometimes can't see dark asteroids, or if they happen to be shiny, can be tricked into thinking they are larger than they are.
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"WISE can see the heat signature from the object, and as long as it has some warmth from the sun, which these objects do, it is very sensitive to dark objects," she said.