The European Space Agency on Wednesday said goodbye to Planck, an observatory which captured headlines and mapped the relic light of the Big Bang, turning off its transmitter in a bittersweet ceremony at the mission's control center in Germany.

Artist's concept of the Planck spacecraft. Credit: ESA
 
Jan Tauber, the scientist who shepherded Planck through competitive proposals, launch delays and scientific splendor, sent the final command to the spacecraft at 1210 GMT (8:10 a.m. EDT) from the European Space Operations Center in Darmstadt, Germany.

"It is with much sadness that we have carried out the final operations on the Planck spacecraft, but it is also a time to celebrate an extraordinarily successful mission," said Steve Foley, Planck's spacecraft operations manager.

Planck operated four-and-a-half years, three times longer than originally planned.

Launched in May 2009 on an Ariane 5 rocket shared with ESA's Herschel telescope, Planck measured the cosmic fingerprint of the Big Bang, detecting subtle variations in background light originating 380,000 years after the genesis of the universe.

The fluctuations in light in the primordial cosmos represent slightly different densities, and the clumps of matter later coalesced to form the earliest galaxies in the universe.

Scientists analyzed Planck's data using an extensive computer chain on the ground, removing light from nearby stars, the Milky Way's galactic plane, and other galaxies to reveal a "baby photo" of the universe.

The afterglow of the Big Bang imaged by Planck is called the cosmic microwave background. ESA released Planck's first image of the CMB in March.

Scientists plan a second data release in 2014.

The anisotropies of the Cosmic microwave background (CMB) as observed by Planck. The CMB is a snapshot of the oldest light in our universe, imprinted on the sky when the Universe was just 380,000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today. Credit: ESA/Planck Collaboration
 
"Planck has given us a fresh look at the matter that makes up our universe and how it evolved, but we are still working hard to further constrain our understanding of how the universe expanded from the infinitely small to the extraordinarily large, details which we hope to share next year," Tauber said.

The Planck mission, an investment of approximately $1 billion, allowed scientists to refine the universe's age to 13.82 billion years. It also changed the understanding of the universe's ingredients, and researchers adjusted estimates of the amount of normal matter, dark matter and dark energy in the cosmos.

"Planck has provided us with more insight into the evolution of the universe than any mission has before," said Alvaro Gimenez, ESA's director of science and robotic exploration. "Planck's picture of the CMB is the most accurate 'baby photo' of the universe yet, but the wealth of data still being scrutinized by our cosmologists will provide us with even more details."

The spacecraft's two instruments were cooled to frigid temperatures just above absolute zero to make the detectors sensitive to the faint CMB signal.

One of the instruments was rendered inoperable in January 2012, when it exhausted its supply of liquid helium coolant. Two other coolers kept Planck's other sensor active until it stopped taking observations Oct. 3 and was deactivated Oct. 19.

Stationed at the L2 Lagrange point about one million miles from the night side of Earth, Planck completed eight full scans of the sky from 2009 until Oct. 3.

Planck project scientist Jan Tauber at the European Space Operations Center in Darmstadt, Germany, to issue the final command to the spacecraft. Credit: ESA
 
Controllers put Planck on a trajectory away from L2 in August, part of an effort to ensure the 13.8-foot-wide spacecraft would stay away from Earth for the foreseeable future.

Over the last week, engineers drained Planck's remaining fuel and configured the observatory for decommissioning.

"We wanted to set a precedent on how to do proper disposal and spacecraft decommissioning," Foley said. "We wanted to drain all the fuel, we wanted to disconnect the batteries, we wanted to get rid of the helium isotopes that have been used to cool the very cool dilution cooler on Planck, and we have patched the software to make sure the transmitters never come on again."

Controllers did not turn off the spacecraft's main computer, and Planck was expected to continue functioning for several months.

"The software runs completely nominally, and the spacecraft will be notionally healthy, but it won't be transmitting, which keeps the airwaves free," Foley said.

Some time in the next three months, Planck's power-generating solar panels will gradually drift away from the sun. Without fuel to point back toward the sun, Planck's computer will lose power and the spacecraft will turn off for good.