After more than three years of probing the secrets of the universe, ESA’s Herschel space observatory – the largest astronomical telescope ever launched – has exhausted its supply of liquid helium coolant and ceased operating.
Essential for cooling the observatory’s highly sensitive instruments to around absolute zero, the telescope’s supply of over 2,300 litres of liquid helium has been slowly evaporating since its launch aboard an Ariane5 rocket on 14th May 2009. Confirmation that the coolant had run out came yesterday (Monday 29th April), when the spacecraft reported a rise in temperature to its ground station in Western Australia.
Named after the German-British astronomer William Herschel, Herschel is equipped with a giant 3.5m diameter primary mirror and was designed to study the formation of stars and galaxies and the relationship between the two.
The telescope has given astronomers the best view yet of the universe at far-infrared and submillimetre wavelengths and has bridged the gap in the spectrum between what can be observed from the ground and earlier space missions of this kind. It has made over 35,000 scientific observations, amassing more than 25,000 hours’ worth of science data from about 600 observing programmes.
Its stunning images of intricate networks of dust and gas filaments within our galaxy have provided an illustrated history of star formation and helped give astronomers a new insight into how turbulence stirs up gas in the interstellar medium, giving rise to a filamentary, web-like structure within cold molecular clouds.
‘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, and allowing us to trace water through the Universe from molecular clouds to newborn stars and their planet-forming discs and belts of comets,’ said Göran Pilbratt, ESA’s Herschel project scientist.
What’s more, whilst the telescope itself may longer be in operation, its huge archive of data is expected to yield many more important discoveries over the coming years. ‘Herschel has exceeded all expectations, providing us with an incredible treasure trove of data that that will keep astronomers busy for many years to come,’ said Prof Alvaro Giménez Cañete, ESA’s director of Science and Robotic Exploration.
ESA controllers will now run some final tests, before switching off the spacecraft’s transponder and sending it off into a heliocentric orbit around the sun.