Herschel Space Observatory Goes Dark

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The ESA’s Herschel Space Observatory

Between the two of us, Amy and I have started many of the Astronomical League’s Observing Programs. Okay, we’ve started a lot more of them than we’ve finished, but that’s a sign of a curious mind, right?

A few AstroBabe meetings ago, we decided that we would break our “no more programs until we finish the ones we have” rule and go after something big – something that would really stretch our observing abilities. We agreed that it was time to start the Herschel, a really, really long-term project.

Unless you are already familiar with AL’s Herschel Observing Program, you have no idea what a commitment this is. If we knock off one or two Herschel objects a week, then in, oh, maybe 300-400 weeks, we’ll have it done. Yes, it’s a big deal, but on the way to finishing the Herschel program, we’ll also complete the Messier Program and the Binocular Messier Program. Three birds with one giant stone.

It seems ironic that we are beginning this quest just as the European Space Agency’s (ESA) Herschel Space Observatory made its last observation. The Observatory was named after William Herschel, the man who discovered infrared radiation in 1800.

Its mission has been to study the formation of stars and early galaxies, and it has surveyed thousands of galaxies during its four-year mission. The Herschel Observatory made over 35,000 observations and collected more than 25,000 hours worth of scientific data on objects that were previously invisible to us.

Launched by an Ariane 5 rocket on May 14, 2009, the Herschel Observatory has been parked at the second Lagrange point, about 930,000 miles from Earth. The school-bus sized observatory detected infrared wavelengths in a wide range of low temperatures, as low as ten degrees above absolute zero at far-infrared and sub-millimeter wavelengths.

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View of the Horsehead Nebula in the constellation Orion by the ESA’s Herschel Space Observatory.

Because heat interfered with its observations, liquid helium was used to chill the temperature of the detectors to nearly absolute zero (-271 Celsius). When it launched, it brought 2,300 liters of this liquid helium along, which weighed 335 kg (739 lbs), nearly 10 percent of its original mass. It has been slowly using up and leaking a bit of that helium everyday.

It had been estimated that the Observatory would run out of helium in late March, but it managed to squeeze one more month of observing beyond that estimate. On April 29, during the spacecraft’s daily communication session with the ground crew in Western Australia, it reported a significant rise in temperature in all of its instruments, which meant it had finally ran out of liquid helium.

The Herschel Observatory’s mission will be carried on by the launch of a number of telescopes with infrared capabilities, including the Japanese Space Agency’s Space Infrared Telescope for Cosmology and Astrophysics (SPICA) telescope (2017), the James Webb Space Telescope (2018), and the ESA’s Ritchey-Chretien telescope (2022).

Until then, there is plenty of data to study. Much of the data the Herschel collected is available through NASA’s Herschel Science Center at http://herschel.esac.esa.int/. There is also more information on the mission itself on the ESA’s own website at http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=51550.

As for the Herschel Observatory itself? Later this month, it will be propelled into a no-return heliocentric orbit where it will take at least 300 years to return to earth on its own. But who knows? Maybe some ambitious future space clean-up crew will collect it and bring it back to Earth and park it in the Smithsonian where our grandchildren can go to see it.

 Lynn