The European Space Agency’s Rosetta spacecraft is now close enough to Comet 67P/Churyumov-Gerasimenko to photograph its own shadow on the surface of the comet. The shadow shows Rosetta as a small fuzzy blob, with an additional area of brightness around it. On its long journey through the solar system, Rosetta seems to have earned a halo.
The comet-chasing spacecraft is in the most exciting phase of its mission. In August 2014, after a journey of billions of miles, it finally reached its carefully planned and executed rendezvous with Comet 67P/Churyumov-Gerasimenko. In November last year, it dispatched its robot lander probe, Philae, to the comet’s surface.
The photograph was taken on February 14, from a height of only 6 km from the comet’s surface. The sun was directly above Rosetta, which allowed it to take photographs of the landscape free of any significant surface shadows. This alignment may also have been responsible for the area of brightness seen around the comet’s shadow, producing an effect known as “opposition surge”.
Comet 67P/Churyumov-Gerasimenko is a periodic comet that completes its circuit of the sun every 6.5 years. Though it is very small (just 4 km across), it was chosen for the rendezvous because its orbit and return dates can be predicted very accurately. It took Rosetta ten years and boosts from the gravitational fields of Earth and Mars to successfully perform the complicated maneuvers to intercept its comet. En route it also performed close flybys of two asteroids, which required careful planning of its flight trajectory.
Comets contain remains the protoplanetary disc out of which the planets of the solar system were formed. As such, they offer important clues to the origins of the planets and the evolution of the solar system. Currently, scientists are looking at the composition of the water found on the comet to discover if it could have been responsible for the creation of the oceans on earth, bringing water to the earth’s surface once it had cooled down after formation. Rosetta will stay on orbit as the comet reaches perihelion in August. The mission is scheduled to end in December 2015.