NASA’s Wide-field Infra-red Survey Explorer (WISE) has just completed it’s second mission, NEOWISE, in which it scans the Solar System for Near-Earth Objects (NEO’s) which could potentially threaten the planet.  WISE was originally launched in December 2009, to perform a full survey of the sky in four infra-red wavelengths.  In the process it discovered not only distant warm objects but also thousands of new previously unseen asteroids.  The incredible sensitivity of the infra-red detectors meant that the probe had to be chilled to a temperature of 260 degrees Celsius below freezing.  WISE was equipped with tanks of coolant which would slowly evaporate and leak, keeping the detectors cold. 

The orbiting infra-red telescope completed its first full scan, photographing the entire sky in all directions, by July 2010.  It was part-way through a second scan (to detect moving objects and any other changes) when the coolant finally ran out.  Without the extreme low temperatures, half of the sensors could no longer operate, and WISE was declared a success and mothballed. 

In October last year, the JPL announced that WISE would be revived and assigned a new mission, NEOWISE, in which is would use its remaining detectors to scan the Earth’s neighbourhood and the asteroid belt to map out small objects within the Solar System.  This second mission, which has now been completed, observed over 150,000 rocky objects, more than 100 comets, and discovered more than 2000 asteroids which orbit near Jupiter (as opposed to being in the main Asteroid Belt).  WISE will now be parked in a polar orbit and put back to sleep, in case it is needed for a third mission.