The end of the Herschel Space Observatory mission
On Monday, April 29, the Herschel Space Observatory exhausted its supply of ultra-cold liquid helium coolant, required to do its most sensitive observations. A ten-year period in which five telescopes gazed at the sky observing the heat of cosmic objects, rather than the light emitted, has come to an end.
Herschel was launched on May 14, 2009 from the European Space Agency launchpad in French Guiana carrying a a 3.5 meter (11.5 feet) mirror, the largest ever flown in space, and launched with over 2,300 liters of liquid helium to support at least a three year mission lifetime. The telescope observed wavelengths of light unobserved by previous instruments. Infrared astronomy is a useful probe of the Universe for three central reasons. Much of the universe is comprised of material which is cold, unlike the hot surface of stars. This is invisible in most of the electromagnetic spectrum unless illuminated by nearby hot objects, but is visible in the infrared. Cold clouds of gas and dust can be mapped directly through infrared observations. Much of the universe is also dusty, and dust extinguishes visible light. Infrared has the ability to reveal the details of events like stellar formation inside obscuring clouds. It permits a full and unbiased census of stellar formation even for extraordinarily distant galaxies. Finally, the universe is expanding, and the most distant objects appear to recede from us at enormous velocities. This shifts much of their emitted radiation towards the red and into the infrared.