January 11, 2012

Planck is getting warmer

On Saturday 14th of January 2012 at 12am, the helium 3 pressure in the Planck reservoirs passed below the minimal threshold required to maintain the HFI focal plane at its record temperature of 100 mK.

Thanks to a very fine Helium valve management, the mission duration have been doubled by the teams in charge of the HFI operations: 36 months of almost continuous observations and 5 consecutive sky surveys in the microwave range instead of 2, with a sensitivity twice that of the specifications.

The last weeks of the "cold" HFI were used to gather the last necessary calibration data just in time before the temperature went up: satellite's spin-speed acceleration, Mars and Jupiter observations.

The temperature progressively increased thanks to smart management valves which controlled the extraction of the last Helium 3 volutes from the reservoirs. So, on January 16th, the HFI's bolometers still displayed a temperature of only 110 mK. This period of a few weeks was used to update calibration measurements of some electronic equipments. Afterwards, the HFI was planned to remain powered during a year to allow the LFI, which operates at 4K, to acquire supplementary measurements in perfectly stable conditions during a mission extension at a higher temperature.

The scientific harvest of Planck's HFI and LFI only just begun and will surely be huge. In January 2011, the first results were released during the first symposium in La Villette, Paris. The catalogue was much awaited by almost the whole astrophysical community and presented many objects such as remote clusters of galaxies, protostars at every stages of formation, valuable statistical information on the cosmic infrared background radiations (the light in the sky which is though to come from all the remote galaxies), etc.

On February 13th-16th 2012, the scientists met again in Bologna to present the new results obtained in these field since the preceding year. The cosmological contents (i.e. the specifications of the cosmic microwave background - CMB - the first light emitted in the Universe) resulting from the first two surveys, the overachieving goal of Planck, will be released in early 2013. Until that time, the scientific teams are finalizing the data processing which is a real sterling work led by the Institute of Astrophysics of Paris. This task involves separating the different astrophysical components (galactic light, cosmic infrared background, clusters of galaxies and CMB) and artefacts produced by the satellite and its motion from the raw measurement.

The task will then continue until at least 2014 to process all the surveys and reach an historical accuracy. Planck is qualified as "ultimate" mission: its sensitivity is not limited by its instrumental performance, but by the photons' noise of the CMB, a natural impassable barrier.

The international Planck-HFI, developed under the responsibility of the Institute of Space Astrophysics in Orsay and involving a lot of CNRS and CEA's laboratories supported by CNES, will continue to be a model in the space history.

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