Washington: ESA`s Herschel space observatory has now run out of its supply of liquid helium coolant, ending more than three years of pioneering observations of the cool Universe.
The event was not unexpected: the mission began with over 2300 litres of liquid helium, which has been slowly evaporating since the final top-up the day before Herschel`s launch on 14 May 2009.
The liquid helium was essential to cool the observatory`s instruments to close to absolute zero, allowing Herschel to make highly sensitive observations of the cold Universe until today.
The confirmation that the helium is finally exhausted came in the afternoon of 29 April 2013 at the beginning of the spacecraft`s daily communication session with its ground station in Western Australia, with a clear rise in temperatures measured in all of Herschel`s instruments.
"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 Gimenez Canete, ESA`s Director of Science and Robotic Exploration.
Herschel has made over 35 000 scientific observations, amassing more than 25 000 hours` worth of science data from about 600 observing programmes. A further 2000 hours of calibration observations also contribute to the rich dataset, which is based at ESA`s European Space Astronomy Centre, near Madrid in Spain.
The archive will become the legacy of the mission. It is expected to provide even more discoveries than have been made during the lifetime of the Herschel mission.
"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 Goran Pilbratt, ESA`s Herschel Project Scientist.