On its way to rendezvous with comet 67P/Churyumov-Gerasimenko (67P, for short), the European Space Agency's (ESA's) Rosetta spacecraft has spied its approaching target and the coma – the "halo" made primarily out of ice and dust that gives the comet its fuzzy appearance – that is developing around its nucleus. At more than 600 million km (373 million miles) from the Sun, the opportunity to observe the early onset of coma production at such distances promises to add much to our knowledge of the life-cycle of a comet as it wends its way around the solar system.
"Rosetta is a big mission for the UK so we’re very excited to see these first images of comet 67P ‘coming to life’," said Dr Chris Castelli, Acting Director of Programmes at the UK Space Agency. “With much of the spacecraft built and designed in the country and UK scientists involved in 10 of the mission’s instruments, we’re looking forward to making history by tracking the evolution of this comet as it swings around the Sun.”
Since leaving Earth in March 2004, and recently awakened from 31 months of deep hibernation, the Rosetta spacecraft has spent more than ten years of its 11-year mission just getting to this point. By the time it reaches its mark, it will have traveled more than 6 billion km (3.7 billion miles), executed four planetary flybys, and made a hazardous trip through the asteroid belt.
The OSIRIS imaging system aboard the spacecraft has now started taking pictures of the volatile gases evaporating from the surface of 67P, which drag waves of myriad tiny dust particles with them to form the coma surrounding the comet. This has led scientists to get even more excited about the prospect of the launch of the Philae probe and its Ptolemy instrument package that is set to touch down on the surface of the comet later this year.
"It’s truly great to see these images and witness the beginning of the comet’s active phase," said Ian Wright, Professor of Planetary Sciences at The Open University. "The Ptolemy instrument team can’t wait to get down on the surface and start making measurements on the body of the comet itself."
Other early observations of 67P have revealed that the comet changes in brightness periodically over the course of several hours, enabling the OSIRIS team to more accurately define its rotational period. As a result, it is now known that one full rotation of the comet takes 12.4 hours, which is approximately 20 minutes shorter than earlier believed.