On 30 September 2016 at 13:19 CEST, the final signal from the Rosetta orbiter was received back on Earth. The ESA mission ended when the spacecraft touched down on Comet 67P/Churyumov-Gerasimenko. The international team of scientists had already said their farewells to the Philae lander back in February 2016, when its prolonged radio silence indicated that it would no longer report back to the team in the control centre at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). Originally, there had been no plans for the Rosetta orbiter to land, and so it was not designed for this purpose. But seven of its instruments were able to acquire data during the descent to the comet’s surface and send it back to Earth. "The Rosetta mission can rightly be described as a milestone in space exploration. The achievements of the scientists and engineers have given us an incredible insight into the history of our planetary system," says Pascale Ehrenfreund, Chair of the DLR Executive Board. "The data and images we have received from Rosetta and the Philae lander will be used as a foundation to plan and to define scientific questions for future missions in the Solar System."
The mission featured several 'firsts' – this was the first time that an orbiter had circled a comet on its journey around the Sun, and Philae was the first spacecraft to land a laboratory and conduct measurements directly on the surface of a comet. "The collision of Rosetta with Comet 67P/Churyumov-Gerasimenko has ended a unique mission that has fascinated us for years. It has given us a first-hand view of what the exploration of celestial bodies is like," says Brigitte Zypries, Parliamentary State Secretary at the German Federal Ministry for Economic Affairs and Energy and Coordinator of Federal Government Aerospace Policy. "The Rosetta mission has delivered to scientists an immensely valuable dataset that will take them many years to analyse and interpret."
The mission's completion was a moving moment for the scientists involved, but equally important to their research: "The idea of flying Rosetta on a collision course with the comet has provided us with additional, interesting data from the immediate vicinity of Churyumov-Gerasimenko, for example, the highest resolution images," says DLR comet researcher Ekkehard Kührt, who heads DLR’s scientific involvement in the mission.
Last data from Rosetta
Since the summer of 2016, the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) repeatedly acquired images during close orbits. Operating the imaging system and transmitting its data were assigned high priority during the orbiter’s gradual descent, as they showed the comet from a distance of just five metres. Measurements conducted in the immediate vicinity of Churyumov-Gerasimenko yielded additional valuable data for the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument, which was designed to determine the composition of gases: "Of course, the gas becomes denser as we get closer to the nucleus – and so determining the constituents was more effective than before," says Kührt, who is also a member of the ROSINA science team. The third highly prioritised instrument kept active during the descent was the Rosetta Plasma Consortium (RPC), which investigated the plasma environment immediately surrounding the comet's nucleus and its interactions with the solar wind. In addition, the microwave instrument MIRO, the GAIDA instrument to analyse dust particles, the UV spectrometer ALICE and the RSI instrument to determine the gravitational field were also active. The results are likely to keep the scientists busy for years to come.
"After more than 20 years of our close affiliation with the mission, collaborating in a tight-knit community like a large international family of scientists and engineers, this moment now comes with a touch of sadness," emphasises Ekkehard Kührt. "But in the end, we are all delighted to have participated in a highly successful mission that has yielded immense quantities of unique data. It will take us years to analyse everything, helping us to acquire greater understanding of comets themselves, as well as the development of the Solar System. The Rosetta and Philae mission will revise our previous knowledge of comets in many different areas."