Planck HFI mission draws to a close
16 January 2012
A false-colour image of the whole sky as seen by Planck. The dust throughout the Galaxy (as seen by HFI) is shown in blue, while hot gas (as measured by LFI) can be seen as red regions across the centre of the image. In the background, the mottled yellow features are relic radiation, called the Cosmic Microwave Background, which contains information about the earliest stages of the Universe. This image is a low-resolution version of the full data set.
Image Credits: ESA, LFI and HFI Consortia (2010)
After an impressive two and a half years of operation, Planck's High Frequency Instrument has finally exhausted one of 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.
Cardiff University researchers, led by Professor Peter Ade, have been heavily involved in the design, build, testing and operation of HFI for over ten years. "We put as much Helium-4 and Helium-3 gas onboard as we could squeeze in and are therefore delighted that the HFI has operated for almost three times its nominal mission lifetime", explained Professor Ade. "This is a testimony to the expertise of the scientific and technical teams who designed, built and operated Planck and its scientific instruments." With the loss of cooling gases the detectors will gradually warm rendering them unusable for scientific purposes. Following a salvo of final tests the HFI instrument will be switched off, although it will remain at a chilly -269 Celsius providing a reference source for the LFI which will continue to operating for at least another year.
Planck's second instrument, the Low Frequency Instrument (LFI), does not need to be as cold, though is still at a nippy -255 Celsius. Astronomers from Jodrell Band Centre for Astrophysics, at the University of Manchester, have played a key role in LFI. "The Low Frequency Instrument will now continue operating for another year", said Professor Richard Davis, of the University of Manchester. "During that time it will provide unprecedented sensitivity at the lower frequencies." It is the combination of both instruments that makes Planck so powerful, and gives cosmologists the best ever view of the Universe on the largest scales.
The scientists involved in Planck have been busy understanding and analysing the data since Planck launched in May 2009, with UK efforts being led by the Cambridge Planck Analysis Centre, based at the University of Cambridge. "The fact that Planck has worked so perfectly means that we have an incredible amount of data," explained Professor Efstathiou. "Analysing it takes very high-performance computers, sophisticated software, and several years of careful study to ensure that the results are correct. In fact, the preparation for this work started years before Planck was even launched." Detailed information about the early Universe is now being extracted from the Planck data, with the first cosmology results expected in early 2013.
Professor Andrew Jaffe, from Imperial College London, is also involved in the analysis through the London Planck Analysis Centre, and said "In the last two and a half years, Planck has collected incredible data directly from the early Universe which we currently decoding. We are honoured to have the chance to continue to work with members of the Planck team, in the UK and abroad, and to use Planck's data to understand the Universe on the very largest scales."
One of the major tasks is identifying which bits of the map are showing light from the early Universe, and which parts are due to much closer objects, such as gas and dust in our galaxy, or light from other galaxies. While the cosmologists consider these "foreground" objects to be an annoyance that need to be removed), for some astronomers they are already providing major astronomical results.
"A side effect of studying the distant Universe is that you get to see everything in the foreground," said Dr Clive Dickinson, from the University of Manchester. "The wavelengths Planck observes make it ideal for studying star formation, both in our own galaxy and in others, and having such detailed maps of the entire sky at such a wide range of wavelengths is provides a treasure trove of information." Astronomers have been pouring over the data and have already confirmed the existence of two additional components of the interstellar medium - the gas and dust from which stars form. There are more results on these foregrounds expected to be released during 2012.
"It has been a privilege to be part of the Planck team", concluded Professor Efstathiou. "The satellite has performed flawlessly since launch and has returned data of exceptional quality. I am sure that we will soon have exciting science results on the early Universe."
Planck maps the sky in nine frequencies using two state-of-the-art instruments, designed to produce high-sensitivity, multi-frequency measurements of the diffuse sky radiation: the High Frequency Instrument (HFI) includes the frequency bands 100-857 GHz (wavelengths of 3mm to 0.35mm), and the Low Frequency Instrument (LFI) includes the frequency bands 30-70 GHz (wavelengths of 10mm to 4mm).
Planck was built for ESA by the prime contractor Thales Alenia Space (Cannes, France) with contributions from space industry drawn from ESA's 18 Member States. Because of differing accounting procedures in the many bodies contributing, precise costings are impossible to give. However, the overall cost to ESA and its Member State institutions as well as cooperating agencies world-wide (including NASA and Canadian Space Agency) in round figures is €600M.
Planck was launched in May 2009 from French Guiana. The first all-sky survey began in August 2009 and the first all-sky map was completed in May 2010. Planck completed five all-sky surveys up until mid-January 2010. A first batch of astronomy data, called the Early Release Compact Source Catalogue, was released in January 2011. At the same time, the initial results on galactic and extragalactic astronomy were presented, and further "foreground science" results will be published throughout 2012. The first cosmological results will be made available to the worldwide scientific community towards the end of 2012.
UK role in Planck
The UK has funded work on Planck both through our subscription to the European Space Agency and nationally through direct instrument technology and exploitation of the scientific data. A number of UK institutes and companies form part of the consortium building the two focal plane instruments, the HFI (High Frequency Instrument) and LFI (Low Frequency Instrument). The Jodrell Bank Observatory at The University of Manchester has produced critical elements of the LFI receiver modules. Cardiff University played a major role in the design, manufacture and calibration of the focal plane of the High Frequency Instrument. STFC Rutherford Appleton Laboratory and west-country space company SEA Ltd. helped build HFI, including its super-cool refrigerator. Various UK research groups including Imperial College London and University of Cambridge form the London Planck Analysis Centre and Cambridge Planck Analysis Centre. All the university groups are now involved in the operation, calibration, analysis and simulation of the Planck data. More information can be found in the Planck briefing document. UK funding for the Planck mission is supplied by the UK Space Agency.
Jodrell Bank's role in Planck
Jodrell Bank Centre for Astrophysics (JBCA) is directly involved with the two lowest frequencies of the Low Frequency Instrument, the 30 and 44 GHz radiometers. These have 4 and 6 detectors respectively, operating at 20K (-253.15°C or -423.67°F). The resolution on the sky is 33 and 27 arc minutes, and the sensitivity 1.6 and 2.4 micro K (over 12 months). The cryogenic low noise amplifiers which are the heart of the radiometers were developed at Jodrell Bank, with help from the National Radio Astronomy Observatory in Virginia, USA.
Dr B. Maffei and Dr G. Pisano are involved in the other focal instrument, the HFI. First at Cardiff University and now at the University of Manchester, they have played a major role in the design, development and calibration of the Focal Plane Unit, in particular the cold optics, in collaboration with the Institut d'Astrophysique Spatiale - France, Maynooth University - Ireland and JPL/Caltech - USA.
The work to understand the Galactic emission seen by Planck is being co-led from Jodrell Bank by Emeritus Professor Rod Davies. A number of projects are led by Jodrell Bank scientists, including Professor Richard Davis and Dr Clive Dickinson. Each of the 14 projects focusses on one aspect of the Galaxy as seen by Planck, including the electrons that gyrate in the Galactic magnetic field, the ionized gas that pervades the interstellar medium and the dust grains that emit across the entire frequency range that Planck is sensitive to. Jodrell Bank is also leading the calibration and identifying systematics in the LFI data.
Further informationFor more information, please see:
For more information please contact
Dr Althea Wilkinson,
Jodrell Bank Centre for Astrophysics,
Alan Turing Building,
The University of Manchester,
Manchester M13 9PL
althea.wilkinson [@] manchester.ac.uk
+44 (0)161 275 4184.
Dr Chris North,
School of Physics and Astronomy,
Cardiff CF42 3AA
+44 (0)129 208 70537
Julia Short, Press Officer, UK Space Agency
Email: julia.short [@] ukspaceagency.bis.gsi.gov.uk
Tel: +44 (0)1793 442 012
Jan Tauber, Planck Project Scientist
Science and Robotic Exploration Directorate
European Space Agency, The Netherlands
+31 71 565 5342.