Mission controllers at ESA’s operations centre in Darmstadt, Germany sent the final command to the Planck satellite on 23 October. Launched in 2009, Planck was designed to tease out the faintest relic radiation from the Big Bang – the Cosmic Microwave Background (CMB). The CMB preserves a picture of the Universe as it was about 380 000 years after the Big Bang, and provides details of the initial conditions that led to the Universe we live in today.

The mission began drawing to a close in August, when the satellite was nudged away from its operational orbit around the Sun–Earth "L2" point towards a more distant long-term stable parking orbit around the Sun. In the last weeks, the spacecraft has been prepared for permanent hibernation, with the closing activities using up all of the remaining fuel and finally switching off the transmitter.

The mission’s instrumentation needed to be maintained at just one-tenth of a degree above the coldest temperature reachable in the Universe, –273.15°C, so that the spacecraft’s own heat did not swamp the signal from the sky. This enabled temperature variations of just a few millionths of a degree to be distinguished in the CMB. But cooling instruments to these extreme temperatures cannot be maintained forever and, indeed, the High Frequency Instrument (HFI) exhausted its liquid helium coolant in January 2012, just as expected. The Low Frequency Instrument (LFI) meanwhile was able to operate at somewhat higher temperatures using the remaining two coolers and continued making observations until 3 October. After conducting post-science activities, it was manually switched off on 19 October.

The mission’s original target was to complete two whole surveys of the sky but, in the end, Planck completed five full-sky surveys with both instruments. Moreover, by mid-August, LFI had completed its eighth survey of the entire sky. The first detailed image of the faint signal from the CMB from Planck was released earlier this year, after foreground emission from our own Milky Way Galaxy as well as all other galaxies had been removed. These latter data resulted in a new catalogue of objects, including many never-before-seen galaxy clusters in the distant Universe.

The 2013 data release provided revised values for the relative proportions of the ingredients of the Universe, namely normal matter that makes up stars and galaxies, dark matter, which has thus far only been detected indirectly by its gravitational influence, and dark energy, a mysterious force thought to be responsible for accelerating the expansion of the Universe.

Link:

Full ESA Press Release: Planck on course for safe retirement

Contact:

Dr. Torsten Enßlin
Max-Planck-Institut für Astrophysik
Tel. 089 30000-2243
E-mail: tensslinmpa-garching.mpg.de

Dr. Hannelore Hämmerle
Pressesprecherin
Max-Planck-Institut für Astrophysik
und Max-Planck-Institut für extraterrestrische Physik
Tel. 089 30000-3980
E-mail: prmpa-garching.mpg.de