ESA Planck instrument loses its cool

Artist's impression of Planck. Credit: Background image: ESA, ESO and STECF. Planck image: ESA/AOES Medialab.

After an impressive two and a half years of operation, Planck's High Frequency Instrument has finally exhausted its onboard coolant gases and reached the end of its very successful mission.

Meanwhile the Low Frequency Instrument, which does not need to be super-cold, will continue taking data with unprecedented sensitivity at longer wavelengths.

Planck’s primary mission is to observe the Cosmic Microwave Background – the afterglow of the Big Bang.

Despite an original mission lifetime of a year, the spacecraft has continued working for almost three years, and has mapped the sky nearly five times.

The expansion of the Universe means that the Cosmic Microwave Background is brightest when seen in microwave light, with wavelengths between 100 and 10,000 times longer than visible light.

To measure such long wavelengths Planck’s detectors have to be cooled to very low temperatures, with the heart of the High Frequency Instrument (HFI) being the coldest place in space.

Professor George Efstathiou, at University of Cambridge and the Planck Survey Scientist, said “Planck is giving us the best ever view of the early Universe, and while the High Frequency Instrument is coming to the end of its mission we have a wealth of data to analyse over the coming months and years.”

Although Planck is an international project, led by the European Space Agency, there is strong involvement from scientists in the UK. Scientists at University of Cambridge, Imperial College, University of Manchester and Cardiff University have been involved in the design, construction and operation of Planck and its instruments for over a decade, and are now heavily involved in analysis of the data.

In addition, one of three refrigeration systems was designed and built at the Science and Technology Facilities Council’s Rutherford Appleton Laboratory near Harwell, Oxfordshire.

The detectors of the High Frequency Instrument (HFI) only work properly when cooled to very low temperatures, and for the duration of the mission have been cooled to 0.1 degrees above absolute zero (-273.15 Celsius) – making them the coldest known place in space! The refrigerator that keeps them cold relies on helium gas, and it is this that has finally been exhausted.