The ESA said it decided to end Rosetta’s mission on the surface of 67P because the comet was heading out beyond Jupiter’s orbit—farther from the Sun than the probe had ever traveled. There would be little power, the ESA said, to operate the craft, and no guarantee it would awake from hibernation when the comet returned to the inner solar system.
“It's like one of those ’60s rock bands; we don’t want to have a rubbish comeback tour,” Matt Taylor, the ESA’s project scientist, told the BBC. “We’d rather go out now in true rock ’n’ roll style.”
Rosetta’s mission was groundbreaking. Since its launch in 2014, the probe orbited the Sun six times. Its almost 5-billion-mile (8-billion-kilometer) journey included three flybys of Earth, one of Mars, and two encounters with asteroids, the ESA said. In November 2014, it landed Philae, a robot on the comet’s surface—the first time mankind ever landed anything on a comet. As my colleague Adrienne LaFrance reported at the time:
The lander's mission was to report back to Rosetta—and, by extension, scientists on Earth—about the composition of its new comet home.
But Philae’s battery soon ran out and that was that—until seven months later, it woke up and began transmitting data back to Rosetta.
The ESA said Friday that data transmitted by Rosetta would keep scientists busy for years. Here’s more:
Many surprising discoveries have already been made during the mission, not least the curious shape of the comet that became apparent during Rosetta’s approach in July and August 2014. Scientists now believe that the comet’s two lobes formed independently, joining in a low-speed collision in the early days of the Solar System.
Long-term monitoring has also shown just how important the comet’s shape is in influencing its seasons, in moving dust across its surface, and in explaining the variations measured in the density and composition of the coma, the comet’s ‘atmosphere’.
Some of the most unexpected and important results are linked to the gases streaming from the comet’s nucleus, including the discovery of molecular oxygen and nitrogen, and water with a different ‘flavour’ to that in Earth’s oceans.
Together, these results point to the comet being born in a very cold region of the protoplanetary nebula when the Solar System was still forming more than 4.5 billion years ago.
“Inevitably, we now have new mysteries to solve,” Taylor, the project scientist, said. “The comet hasn’t given up all of its secrets yet, and there are sure to be many surprises hidden in this incredible archive. So don’t go anywhere yet—we’re only just beginning.”