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ESA retires Herschel space telescope as too hot to handle

Lonely star-spotter stranded 1.5 million km from Earth

The European Space Agency has formally retired the Herschel space telescope after nearly four years of operation, and has placed it in a parking orbit that will keep it out of Earth's way.

Herschel's at rest at last

Herschel's at rest at last

Hershcel, along with the Planck space telescope, was launched on May 14, 2009, and is stationed 1,500,000 kilometers (930,000 miles) away at the second Lagrange point between the Earth and the Sun, where the gravitational forces of the two bodies cancel each other out.

The space telescope used liquid helium to cool its internal instruments to -271°C so that they could see on far-infrared and sub-millimeter wavelengths, giving unparalleled views of the universe around us. The telescope has now burned through its allotted 2300 liters of helium and is too hot to make accurate observations, its handlers report.

"While the observations have ceased, Herschel as a science mission is by no means over," said Göran Pilbratt, project scientist at the European Space Agency (ESA).

"Most of Herschel's data are publicly available already," Pilbratt said. "We will continue supporting the community exploiting the data, collecting and producing the best possible data products in the form of maps, spectra, and various catalogues to benefit all astronomers. We are looking forward to the multitude of great discoveries that are still ahead of us."

Orion B molecular cloud

Sights the original Herschel would have killed to see

Herschel has made over 35,000 scientific observations, generating more than 25,000 hours-worth of data for about 600 programs, much of which is still being processed. Over 600 scientific papers have been published based on its findings and many more are expected, the ESA said.

The telescope used a 3.5 meter mirror – the largest ever deployed in space – which could then feed data back to three measurement units operating at different ends of the spectrum. The instrument was powered by solar arrays and has provided an unparalleled look at the earlier state of the universe.

"Herschel has allowed us to see for the first time a huge population of intensively star-forming galaxies that make up about half of the entire star formation budget of the Universe," said Matt Griffin from Cardiff University.

Herschel star census

Oh my god, it's full of stars

"Stars form in clouds of gas and dust, and most of the energy released by forming stars is absorbed by the dust grains, causing them to warm up. We can detect this warm dust with Herschel and so measure the energy produced by the young stars."

While the telescope's primary mission is stars, the instrument has also been useful for settling matters closer to home. Herschel analyzed the Hartley 2 comet as it went past and found that it not only contained water, but that the H2O matched the isotopic composition of water here on Earth, suggesting our oceans were delivered from the stars over time.

"The comparison between the composition of water in comets and on Earth's oceans may have far-reaching implications: if comets did contribute to enriching our planet with water, they might also be responsible for the delivery of other species, such as the carbon- and nitrogen-based compounds that are of great importance to the emergence of life," said Frank Helmich from SRON Netherlands Institute for Space Research.

Hartley 2 comet

The Hartley 2 comet, or why you can go to the beach

The defunct telescope will now use the last of its propellant to move into a parking orbit that will keep it out of Earth's way for the next few hundred years, although smashing it into a planet was also considered. Hopefully by then we'll have the space-faring capability to retrieve it and bring it home to take its well-earned place in a museum or suitable institute of learning. ®

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