Planck spacecraft's first look back in time
Planck, an observatory stationed in space beyond the Earth–moon system, has begun its task of probing the universe as it looked when it was just a sliver of its present age. Last month the European Space Agency probe started to map the cosmic microwave background, the relic radiation from the early universe, taking this "first light" survey between August 13 and August 27. (Planck's preliminary data are superimposed on an optical-light image of the sky.) As the spacecraft spins and follows its loop around the sun, it will build a complete map of the sky in about half a year.
The cosmic microwave background is a wash of electromagnetic radiation that has been propagating through the universe for more than 13 billion years. It contains information about the state of the universe about 380,000 years after the big bang, when the background radiation was emitted. By measuring subtle temperature differences across the microwave background (indicated by color variations in Planck's map), astronomers can see what kind of universe this relic light emanated from.
A similar probe launched in 2001, NASA's Wilkinson Microwave Anisotropy Probe (WMAP), helped nail down the age of the universe as well as the relative abundances of ordinary matter, dark matter and dark energy. Planck will build on those WMAP observations and provide data to test competing theories of inflation, the hypothesized rapid expansion of the universe that followed hot on the heels of the big bang.