An ESA spacecraft launched in 2009 May to study fluctuations in the cosmic microwave background, caused by slight density differences in the early Universe from which galaxies formed. Planck, named after the German physicist Max Planck (1858–1947), carries a 1.5-m mirror to focus microwaves onto two detectors which register variations in the temperature of the background radiation of a few millionths of a degree, with an angular resolution better than 10 arcminutes. Planck was launched on the same rocket as the Herschel Space Observatory, another ESA scientific mission, but the two separated once in space and operate independently at the L2 Lagrangian point, 1.5 million km from Earth in the direction away from the Sun.
http://sci.esa.int/science-e/www/area/index.cfm?fareaid=17 ESA mission website.
Subjects: Astronomy and Astrophysics.