Herschel closes its eyes on the Universe

29 April 2013 - ESA's Herschel space observatory has exhausted 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 this afternoon 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," says Prof. Alvaro Giménez Cañete, 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.