The deep-space Herschel telescope, launched four years ago to observe the creation of stars, will soon be going out of service as its supply of instrument coolant runs out, the European Space Agency said on Tuesday.

When it was launched in May 2009, Herschel became the largest and most powerful infrared telescope in space and has made several discoveries, ranging "from starburst galaxies in the distant universe to newly forming planetary systems orbiting nearby young stars", the ESA said.

The agency said in a statement it was not possible to give an exact date of when supplies of the liquid helium coolant will be exhausted, but said it expects it to happen in the coming weeks.

The supplies of the coolant determine Herschel's lifetime as detectors of the telescope's camera and spectrometer equipment need to be cooled to minus 271 degrees Celsius (minus 456 degrees Fahrenheit).

"It is no surprise that this will happen, and when it does we will see the temperatures of all the instruments rise by several degrees within just a few hours," Herschel mission operations manager Micha Schmidt said.

When it was launched, the ESA calculated the telescope would be in operation for about 3.5 years.

Once the coolant is exhausted, the telescope will still be able to communicate with its ground stations for some time, but will be sent into a "parking orbit" around the sun in May, the ESA said.