After 12 years, ESA's Rosetta deep-space probe ended its mission today as it made a controlled impact on the Ma'at region of comet 67P/Churyumov-Gerasimenko. According to mission control in Darmstadt, Germany, the unmanned orbiter struck the surface at 11:20 GMT (1:20 pm CEST) after spending two years studying the comet as it swung round the Sun before heading back into the outer Solar System. Because Rosetta is 720 million km (447 million mi) from Earth, the landing was confirmed about 40 minutes after it took place, and the time reflects the moment of reception.
Today's landing follows a series of maneuvers to place the orbiter on target. Yesterday at 20:50 GMT (10:50 pm CEST), Rosetta carried out its 208-second collision burn, while it was only 19 km (12 mi) from 67P and set itself on an intercept course. Today at 08:00 GMT (10:00 am CEST), it received its last commands from Earth to fine-tune its course and confirm its landing time based on data sent back by its navigation camera.
ESA decided to land Rosetta on 67P because it and the comet are moving away from the Sun and will soon cause the spacecraft to shut down as its solar panels are unable to generate sufficient power to keep its systems running. Because the batteries will soon drain, Rosetta's electronics will freeze and the probe will be lost for good. It was therefore decided to use its last hours as a way of taking a final, very close look at 67P.
During the descent, the spacecraft turned both its high-resolution and navigation cameras on the comet and it collected data from its 11 scientific instruments until the very end. In its final hours before impact, Rosetta analyzed gases and dust closer than was safe to do at any time before.
NASA says that the Ma'at region is of interest to scientists because of its 330 ft (100 m) wide active pits that hold structures that could be the "cometesimals" that collided billions of years ago to create the comet. It's hoped that during its descent, Rosetta was able to capture and transmit back images of the area.
Rosetta lifted off atop an Ariane 5 rocket on March 2, 2004 at the Guiana Space Centre in French Guiana. It arrived at 67P/Churyumov-Gerasimenko on August 6, 2014 and was the first mission to escort and orbit a comet as it approached the Sun on its highly elliptical orbit. During its two-year sojourn, the probe would go in and out of orbit at various distances or fly alongside on a parallel trajectory. Because 67P has an escape velocity of only 1 m/s (3 ft/s), even the small thrusters on Rosetta had no problem carrying out such maneuvers.
On November 4, 2014, it carried out another first when it launched its Philae lander in an attempt to make the first soft landing on a comet. Unfortunately, the washer-sized spacecraft bounced several times before coming to rest on its side. Though it was able to send back images and telemetry for about 60 hours, it was unable to charge its batteries and went silent. Though contact was reestablished intermittently, communications were formally terminated on July 26.
ESA says that Rosetta struck the system at about 90 cm/s (2 mph), which isn't very fast, but the spacecraft is very fragile and was very likely damaged, though not severely. However, because of the danger of its radio interfering with deep space tracking networks, Rosetta was programmed to shut down completely on impact and it was the loss of signal as monitored by NASA's Canberra tracking station at that moment that marked the mission end.
"The European Space Agency's Rosetta Mission is a magnificent demonstration of what excellent mission design, execution, and international collaboration can achieve," says Geoff Yoder, acting associate administrator for NASA's Science Mission Directorate. "Being neighbors with a comet for more than two years has given the world invaluable insight into these beautiful nomads of deep space. We congratulate ESA on its many accomplishments during this daring mission."
The animation below shows what Rosetta's impact might have looked like.