Today, I have some unfortunate news. The Herschel Space Observatory, the largest and most sophisticated infrared telescope ever launched, is being retired after nearly four years. This call for retirement came when the telescope finally exhausted its supply of liquid helium – the coolant responsible for chilling the observatories instruments allowing it to make the most detailed observations of the universe in infrared ever seen. Herschel’s main mirror was 3.5 meters across, or about 1.5 times larger than the mirror on Hubble. Herschel was designed to view the universe in the far-infrared and sub-millimeter wavelengths of the electromagnetic spectrum.
Herschel launched in May of 2009 and given a mission expectancy of three and a half years. This mission duration was determined by the amount of liquid helium on board the telescope. In order to obtain the extremely clear, high-resolution, images – as well as observing previously invisible and cooler regions of the galaxy and universe – scientists and engineers were hoping for, the instruments onboard Herschel need to be cooled to a chilly -271°C; near absolute zero. As you’ve probably already concluded, the onboard supply of liquid helium is responsible for cooling the telescope. Of course, thermodynamics gets in our way, so this supply of helium has been evaporating over the last four years until last week when the ESA announced this supply was depleted.
Herschel’s mission has been an incredible success and it has revolutionized our understanding of the universe. The telescope has performed approximately 35,000 scientific observations over the course of about 25,000 hours collecting a ton of data in the process; all together, about 10% more than the original mission specifications. Herschel has shown us the processes of star formation be peeling away the curtain of dust covering stellar nurseries, allowed us to see how galaxies formed and evolved in the early universe, pulled back the vale on the chemical composition of the atmospheres and surfaces found within our own solar system (including planets, moons, and comets), looked at the chemical composition of the entire universe, resolve the infrared cosmic background radiation, and allowed us to make observations into the far-infrared spectrum helping us to see into the submillimeter wavelengths.
Because of the predictably limited lifespan of the telescope, scientists carefully planned Herschel’s missions enabling it to take all of the high-priority observations that required the clearest imaging first. Those observations were completed ahead of schedule giving scientists the opportunity to move ahead to secondary observations. Over the last few weeks, Herschel has been prepared for its eminent decommissioning. One of the last tasks to complete will be directing Herschel to enter into a long-term parking orbit around the Sun.
Herschel may be retiring, but scientists are only getting started on the data. As Goran Pilbratt, one of Herschel’s Project Scientists, says, “the peak of scientific productivity is still ahead of us, and the task now is to make the treasure trove of Herschel data as valuable as possible for now and for the future.”
Sources and further reading:
Image Credit: ESA/Herschel
Clockwise from top-left corner: Rosette Cloud, Andromeda Galaxy, Whirlpool Galaxy, W3
More Herschel images: