|A strange new world: Comet 67P/Churyumov-Gerasimenko as seen by the Rosetta spacecraft, which became the first spacecraft to orbit a comet on 6th August. Image Credit: ESA.|
|The surface of Comet 67P/Churyumov-Gerasimenko taken from a distance of 100km with Rosetta's OSIRIS science camera. Image Credit: ESA|
Previous missions and telescope observations have revealed that comets like Churyumov-Gerasimenko are "dirty snowballs", irregular mixes of ice and dust. Working out how that chemical composition and the varying geological activity of the comet has produced such a landscape is one of the questions that Rosetta will try and answer.
Unlike most space missions, Rosetta's initial orbit around Comet 67P doesn't follow the standard circle or ellipse. Until the mass of the comet can be measured by observing its gravitational pull on Rosetta, the ground controllers at ESA don't know exactly what manoeuvres will be needed to reach a stable orbit.
Instead, as the video shows, Rosetta will fly around the comet in a strange triangular orbit, flying in hyperbolic arcs with thruster burns at each corner. From there the orbit will be slowly lowered, until the spacecraft is in an ellipse just 10km above the surface of Comet 67P.
|An overexposed image of Comet 67P taken on 2nd August, revealing jets of material streaming from the surface. Image Credit: ESA|
This activity will continue to increase during Rosetta's time at the comet. By the time Churyumov-Gerasimenko reaches perihelion, the closest point in its orbit to the Sun in a year's time, the plumes will have grown into a characteristic tail, or coma.
Arguably the most exciting phase of the mission is still to come. In November Rosetta will deploy the Philae lander, a fridge-sized box that will attempt to become the first man-made object to land on a comet. Rosetta has already made an initial search of Churyumov-Gerasimenko for possible landing sites, shown as green cricles in the video. Over the next few months this will be narrowed down to one area for Philae to target, guiding itself in with a pair of harpoons.
With a successful orbital insertion, the Rosetta mission is shaping up to be one of the most exciting space missions ever carried out. The pictures and data that it is returning are already fantastic, and I'm sure I'll write about it again as the mission continues.
P.S. Last time a wrote about Rosetta, I was contacted by a group working on a website where you can see a visualisation of the whole mission, charting the entire ten-year voyage up until now. I recommend a look.
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