At the beginning of this week it was confirmed that ESA’s Herschel space telescope has run out of the liquid helium that kept its instruments at the very low temperatures needed for them to work. The rise temperatures marks the end of its mission after nearly four years of work.

The Herschel space telescope was launched on May 14, 2009 on an Ariane 5 ECA rocket. It was an extraordinary event because there was a multiple launch that also brought into orbit the Planck Surveyor, another protagonist of the research on the universe in recent years. Both of them were placed on Lissajous orbits in the second Lagrange point of the Sun-Earth system, about 1.5 million kilometers (930,000 miles) from Earth.

The goal of the Herschel space telescope was to study the formation of galaxies in the early universe and their evolution, the formation of stars, the chemical composition of planets, satellites and comets and the molecular chemistry of the universe. To do this it used a primary mirror 3.5 meters in diameter, the largest for an infrared space telescope, and very sophisticated instruments.

Herschel was equipped with two cameras with spectrometers: PACS (Photodetecting Array Camera and Spectrometer) and SPIRE (Spectral and Photometric Imaging Receiver), capable of observing infrared light with a sensitivity never seen before, and with the very high resolution spectrometer HIFI (Heterodyne Instrument for the Far Infrared).

To avoid the heat of Herschel space telescope to disturb its own observations because of its infrared emissions, it was necessary to keep its instruments at temperatures close to absolute zero. 2,300 liters of liquid helium have kept the temperatures at the required level for almost four years but over time the refrigerant evaporated.

The Herschel space telescope has made more than 35,000 scientific observations for more than 25,000 hours of data. Its targets have been many and diverse, from the ring around the star Fomalhaut to the water in Jupiter‘s stratosphere. The amount of data is so big that astronomers can study them for a few more years.

Because of the need to keep Herschel’s instruments at very low temperatures, its mission had a deadline. In the end, its life lasted a little longer than it was expected and the depletion of liquid helium was now expected from day to day. For some time, some technical tests will be conducted on this Space Telescope and in a few weeks it will be entered an orbit around the Sun, so it won’t be a hazardous piece of space garbage.

In addition to its great astronomical results, the Herschel space telescope allowed gaining technological advances needed to build it. Some of the future space missions will benefit from those advances, such as the James Webb Space Telescope, which surely will allow us to discover more secrets of the universe.

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