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Herschel closes its eyes - for good

by Bruno Van de Casteele

May 5, 2013

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Donate ESA, the European Space Agency, announced several days ago that their infrared space observatory, Herschel, has gone blind. The probe was specialized in observing near-infrared and sub-millimeter wavelengths, but had to be cooled to almost absolute zero in order to observe. This cooling was assured by an initial stock of 2300 liters of liquid helium, but this has evaporated and is now gone. Basically, the probe is no longer able to observe anything, and has to be written off.

Not that it was a failure.

In fact, the depletion of the stock of Helium was expected to happen any day now. Launched in 2009, the 3.5 m mirror has really shown its worth in observing early star formation. And of course deliver stunning photographs like the one above. ESA claims that about 25 000 hours of observations have been amassed, not bad for a cost of only 1 billion euros. ESA expects that this dataset will still be used over the coming years, and might harbour even more discoveries.

Still, Herschel will be missed. It was a stunning example of space observation with high quality optics and scientific instrumentation. ESA is in the course of shutting it down and parking it in a stable orbit. No worries, the probe is at a Lagrange point 1.5 million kilometers away and will not fall back to Earth.

But there are no space replacements coming soon. There is the ALMA array, just recently operational and specialised in sub-millimeter wavelengths, based in Chili. And there is also the SOFIA telescope, mounted in a Boeing 747 (I blogged about this earlier) for near-infrared observation.

This last one has the advantage of being refuelable, but the big disadvantage of being really close to Earth and not being as big (for obvious reasons) as Herschel. The flying telescope celebrated its 100th flight this month, and discovered something remarkable. A star estimated at being 20 times the mass of our Sun was observed as forming like a much smaller star.

This was observed as a simple contraction of the interstellar cloud it was in, and was contrary to models and thus scientific understanding. Scientists would have expected it to contract in a rapid and very chaotic matter. So this discovery, remarkable in itself, will give rise to new theories and new models, that will help us understand better how stars of all sizes form. And so science carries on, using the tools at its disposition.

by Bruno Van de Casteele

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