The European Space Agency’s Herschel space observatory -- the largest, most powerful infrared telescope ever flown in space -- has run out of liquid helium coolant, ending more than three years of pioneering observations of the distant, “cool universe.”
Herschel was highly sensitive to a wide range of low temperatures, from a few hundred to less than ten degrees above absolute zero -- operating at far-infrared and sub-millimeter wavelengths. To observe cold regions with high sensitivity, liquid helium was used to cool the instruments to nearly absolute zero (or -271 degrees Celsius).
We knew this day would come. The mission began with over 2,300 liters of liquid helium -- which weighed 335 kg, nearly 10 percent of Herschel's mass at launch on May 14, 2009. The helium has been evaporating ever since the final top-up the day before.
Earlier this week, the temperature rose in all of Herschel’s instruments. Later this month, the spacecraft will be propelled to a stable parking orbit around the sun, where it will remain indefinitely.
The observatory was named after astronomer William Herschel who discovered infrared radiation in 1800 -- the very radiation that his namesake telescope used to explore cold, dark regions of the universe, Los Angeles Times explains.
Herschel's chief goal was the study of star formation throughout the cosmos, surveying thousands of galaxies across a wide span of the universe's history.
"Herschel has offered us a new view of the hitherto hidden universe, pointing us to a previously unseen process of star birth and galaxy formation,” says Göran Pilbratt, Herschel Project Scientist, "and allowing us to trace water through the universe from molecular clouds to newborn stars and their planet-forming discs and belts of comets."
The James Webb Space Telescope will image in infrared, Popular Mechanics reports, but won't launch until 2018. NASA and ESA plan to partner with Japanese space agency JAXA on proposed infrared telescope SPICA, to launch in 2017.