Rosetta and the Rubber Ducky: arrival at comet Churyumov-Gerasimenko

6 August 2014 by Joanna Barstow

"Rubber Ducky". Image courtesy of ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Today, August 6th 2014, marks a significant milestone in European exploration of our solar system. After a 10-year, 6 billion-kilometre journey, the European Space Agency Rosetta spacecraft achieved a successful rendezvous with comet 67P/Churyumov-Gerasimenko. At 10 am this morning, Rosetta fired its rockets and altered its trajectory to go into a series of triangular passes around the comet. During these passes, data will be gathered that allow mission scientists to decide on an appropriate site for the Philae lander, due to harpoon itself to the comet in November.

Comet close-up. Image courtesy of ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Incredible close-up images have been sent back to Earth already since Rosetta's arrival this morning. Comet 67P has a craggy, battered surface. But the most surprising discovery came a few weeks ago when Rosetta started to get close enough to resolve the comet's shape; it turns out that 67P might actually be two objects that fused together at some point in the past. The 'neck' joining the two sections is noticeably brighter than the rest of the comet, meaning that it may have a different composition. Over the last few weeks the strange shape has become more and more obvious, leading 67P to be rechristened as the "Rubber Ducky" comet - albeit one that has undergone a particularly violent bathtime episode.

"Rubber Ducky" - upside down in this image. Image courtesy of ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

One of the key challenges of the coming months for the Rosetta team will be finding a safe spot on the comet's surface for the Philae lander to touch down in November. Comets are made of a mixture of ices and rock, and tend to have fairly low densities. This means that the gravitational attraction of 67P won't be sufficient for Philae to simply land on the surface - instead, Philae must anchor itself by shooting two harpoons into the surface of the comet. The lander will then begin its work analysing the composition of the comet's nucleus, in the first study of its kind.

As well as the cameras that are providing us with so many wonderful pictures of the comet, Rosetta and Philae have many scientific instruments on board. These are designed to investigate the thermal properties, composition of the nucleus and coma, interior structure, dust environment and interaction of the comet with the solar wind. Oxford is involved with the VIRTIS instrument on the orbiter; VIRTIS is a mapping spectrometer, which means it takes a series of images in lots of different wavelengths of visible and infrared light. This instrument can detect absorption due to different gases in the coma of 67P, and can map the comet's surface properties by measuring the way in which sunlight is scattered off the surface.

We want to investigate comets like 67P because they may provide clues about the formation and history of the solar system. Comets, unlike planets, are fairly primitive bodies that haven't undergone many changes since the solar system was formed, so their chemical composition is a bit like a fingerprint of the solar system as it was then. We also think that comets may be responsible for the Earth being such a pleasant place for us to live; impacts from these water-rich objects may have increased Earth's water budget, and they may have changed our atmosphere too. There is even speculation that comets delivered the organic compounds that form the building blocks of life. Studying 67P will help us get a little closer to answering these questions.

For more information and updates about Rosetta, see the ESA page here. You can also follow Rosetta and Philae on Twitter - @ESA_Rosetta and @Philae2014

Categories: solar system | comets | space exploration