The target of ESA’s Rosetta mission has started to reveal its true personality as a comet, its dusty veil clearly developing over the past six weeks.
A new sequence of images of comet 67P/Churyumov–Gerasimenko was taken between March 24 and May 4, as the gap between craft and comet closed from around 3.1 million miles (5 million kilometers) to 1.2 million miles (2 million kilometers). By the end of the sequence, the comet’s coma extends about 800 miles (1,300 kilometers) into space. By comparison, the nucleus is roughly only 2.5 miles (4 kilometers) across, and cannot yet be ‘resolved.’
Comet 67P/Churyumov–Gerasimenko's coma has developed as a result of the comet moving progressively closer to the sun along its 6.5-year orbit. Even though it is still more than 373 million miles (600 million kilometers) from the sun – four times the distance between Earth and sun – its surface has already started to warm, causing its surface ices to sublimate and gas to escape from its rock–ice nucleus.
The escaping gas also carries a cloud of tiny dust particles out into space, which slowly expands to create the coma. As the comet continues to move closer to the sun, the warming continues and activity rises, and pressure from the solar wind will eventually cause some of the material to stream out into a long tail.
The Optical, Spectrocopic and Infrared Remote Imaging System (OSIRIS), and the spacecraft’s dedicated navigation cameras, have been regularly acquiring images to help determine Rosetta’s exact trajectory relative to the comet. Using this information, the spacecraft has already started a series of maneuvers that will slowly bring it in line with the comet before making its rendezvous in the first week of August. Detailed scientific observations will then help to find the best location on the comet for the spacecraft's Philae lander to descend to the surface in November.
Comets are time capsules containing primitive material left over from the epoch when the sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in-situ observations, the Rosetta mission should become a key to unlocking the history and evolution of our solar system, as well as answering questions regarding the origin of Earth’s water and perhaps even life. Rosetta will be the first mission in history to rendezvous with a comet, escort it as it orbits the sun, and deploy a lander.
ESA member states and NASA contributed to the Rosetta mission. Airbus Defense and Space built the Rosetta spacecraft. NASA's Jet Propulsion Laboratory, Pasadena, California, manages the U.S. contribution of the Rosetta mission for NASA's Science Mission Directorate in Washington.
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