The Planck spacecraft is 4.2 meters high and has a maximum diameter of 4.2 meters, with a launch mass of around 1.9 tones. Planck will help provide answers to one of the most important sets of questions asked in modern science - how did the Universe begin, how did it evolve to the state we observe today, and how will it continue to evolve in the future? Planck's objective is to analyze, with the highest accuracy ever achieved, the remnants of the radiation that filled the Universe immediately after the Big Bang, which we observe today as the Cosmic Microwave Background.

Planck is equipped with a passive cooling system that brings its temperature down to about -230°C by radiating heat into space. Three active coolers take over from there, and bring the temperature down further to an amazing low of -273.05°C, only 0.1°C above absolute zero - the coldest temperature theoretically possible in our Universe.

Such low temperatures are necessary for Planck’s detectors to study the Cosmic Microwave Background (CMB), the first light released by the universe only 380 000 yrs after the Big Bang, by measuring its temperature across the sky.

The detectors will look for variations in the temperature of the CMB that are about a million times smaller than one degree – this is comparable to measuring from Earth the heat produced by a rabbit sitting on the Moon. This is why the detectors must be cooled to temperatures close to absolute zero (–273.15°C, or zero Kelvin, 0K).

Details on the different stages of the cool-down process are available via the 'Planck in depth' link at bottom.

At the start of yesterday’s maneuver, Planck was located 1.43 million km from Earth.

Adapted from materials provided by European Space Agency ESA

Image: This artist's view shows the combined focal plane of the two instruments on board ESA's Planck spacecraft. The High Frequency Instrument (HFI) is visible as a circular forest of horns at the centre, surrounded by the Low Frequency Instrument (LFI) ring of horns.

The two instruments detect the collected radiation in different ways. LFI is designed to convert the lower energy microwaves into electrical voltages, rather like a transistor radio. HFI works by converting the higher energy microwaves to heat, which is then measured by a tiny electrical thermometer. The instruments share a common telescope.