The detectors of Planck's High Frequency Instrument reached their amazingly low operational temperature of -273.05 degrees Celsius (-459.49 degrees Fahrenheit), making them the coldest known objects in space. The spacecraft has also just entered its final orbit around the second Lagrange point of the sun-Earth system, called L2.

For more information, go to the story on ESA's Planck site at http://www.esa.int/SPECIALS/Planck/SEM0Y5S7NWF_0.html