CometWatch from Gaia

This blog post is based on an image release published on the ESA Space Science portal . On 14 September 2015, Comet 67P/Churyumov Gerasimenko was imaged by Gaia, ESA's billion star surveyor. Located at the Lagrange point L2, 1.5 million km away from Earth in the opposite direction from the Sun, Gaia scans the entire sky about every three months to map the positions and motions of a billion stars in our Galaxy. In the process, the satellite also picks up objects much closer to home, such as asteroids and comets in the solar system, gathering data that will be used to determine their orbits to unprecedented accuracy. Gaia is optimised to detect stars, which appear as point sources in its camera, and measure their properties, but it does not routinely return images of celestial objects. To acquire an image of a particular object, a special trick can be used. This is what Gaia astronomers did to ensure that, when the satellite scanned the patch of the sky including Rosetta's comet, the star-mapper camera would capture an image of this iconic object. “Comet 67P/C-G had just passed its perihelion on 13 August, and calculations predicted that the patch of the sky containing the comet and Rosetta would be scanned by Gaia on 14 September,” comments Fred Jansen, Gaia mission manager and former Rosetta mission manager. “It was a remarkable occasion: Gaia and Rosetta, two ESA science missions separated by over 260 million kilometres, one looking at the other and its object of study.” For this special occasion, the astronomers made sure that Gaia’s star-mapper camera would cover that patch of the sky using a special mode in which a full image is recorded and transmitted to the ground instead of point sources only, as in Gaia's normal science mode. “This […]

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