My favorite thing about the Wide-Field Infrared Survey Explorer (WISE) is how it keeps its camera cold: the satellite's detector array is surrounded by solid hydrogen.
Some reference points:
- absolute zero: 0 kelvins (the coldest anything can be; the absence of all heat)
- avg temperature of space: a little less than 4 kelvins
- temperature of a satellite with the sun shining on it: probably over 300 kelvins
- temperature of the WISE camera in its hydrogen chamber: 17 kelvins
The solid hydrogen is supposed to stay solid for 10 months, says the official WISE satellite site. That's enough to map most of the sky more than once so astronomers can observe celestial motions and fluctuations from extra-solar planets, dark energy acceleration, etc. Here is a picture of the Heart and Soul Nebula from WISE:
(project scientist Peter Eisenhardt stands next to the fully assembled WISE satellite http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=8763)
Comments