Comet 67P鈥檚 activity is clearly visible in the hours leading up to its closest approach to the sun. This series of images was captured by Rosetta鈥檚 OSIRIS camera on 12 August (Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)
It鈥檚 a day for cometary celebration. The European Space Agency鈥檚 Rosetta spacecraft has been orbiting comet 67P/Churyumov鈥揋erasimenko for a little over a year now, and today it accompanies the comet as it makes its closest approach to the sun, known as perihelion.
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Comet 67P at the moment it reached perihelion, at 2.03 GMT this morning (Image: ESA/Rosetta/NAVCAM 鈥� CC BY-SA IGO 3.0)
鈥淚t鈥檚 really a fantastic milestone that鈥檚 been achieved by our Rosetta today,鈥� said ESA project scientist Nicolas Altobelli in a to mark the occasion.
It鈥檚 the first time a spacecraft has monitored a comet up close as it moves from its dormant phase to heated activity.
A jet of gas and dust on 29 July, as the comet warmed up ahead of perihelion (Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)
As the comet moves closer to the sun, warming gas streams from its surface as in the . Just yesterday the team saw another very bright gas jet coming out from the surface (pictured below).
Even at their closest, 67P and Rosetta keep a safe distance from the sun. The pair passed 186 million kilometres from the sun at 2.03 GMT this morning. That鈥檚 even further out than Earth, which is 150 million kilometres distant.
But the comet鈥檚 most active period will actually be over the next couple of days as the surface warms.
The amount of water streaming off 67P has increased a thousand times since Rosetta鈥檚 arrival last year, said Holger Sierks, who oversees Rosetta鈥檚 main camera. 鈥淓very day you could fill ten Olympic swimming pools,鈥� he says.
These outbursts take cometary material along for the ride 鈥� on 30 July the team saw a chunk, possibly 1 metre in size, flying off the comet 鈥� something that had never been observed before. 鈥淚t鈥檚 great to see this for the first time ever,鈥� said Sierks.
(Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)
The change in illumination as the sun switches sides relative to the comet means the team has been able to map its entire surface, including regions that were previously dark. The team has named four of these regions: Anhur, Wosret, Sobek and Kohnsu.
You can explore the surface of 67P for yourself with a produced by ESA to mark perihelion.
Perihelion has also changed the levels of different types of molecules streaming off of 67P, says Joel Parker of the Southwest Research Institute in San Antonio, Texas. He has had a busy month as he works on both Rosetta and NASA鈥檚 New Horizons mission, which flew past Pluto in July. He notes similarities between 67P and Pluto鈥檚 lumpy moon Hydra, which was imaged up close for the first time by New Horizons. 鈥淚t鈥檚 been an adventure, it鈥檚 been great.鈥�
It鈥檚 not all celebrations, however, as the mission team is still trying to make contact with the Philae lander. The team has had no signal from it for more than a month now. 鈥淚t is quite worrying for us,鈥� said Philae operations engineer Barbara Cozzoni. The activity on the comet around perihelion makes it difficult for Rosetta to get close enough to hear Philae, but the team remains hopeful. 鈥淲e are working hard to get some science from Philae,鈥� she said.
