The European Space Agency's (ESA) Rosetta spacecraft, which back in January awoke from 957 days hibernation on its way to rendezvous with comet 67P/Churyumov-Gerasimenko, has now started its first instrument observations. Included in these instruments are three NASA science packages; MIRO, ALICE, and IES, all of which have started sending science data back to Earth.

"We are happy to be seeing some real zeroes and ones coming down from our instruments, and cannot wait to figure out what they are telling us," said Claudia Alexander, Rosetta's US project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. "Never before has a spacecraft pulled up and parked next to a comet. That is what Rosetta will do, and we are delighted to play a part in such a historic mission of exploration."

Since leaving Earth in March 2004, the Rosetta spacecraft has traveled more than 6 billion km (3.7 billion miles) in an attempt to be the first spacecraft to successfully rendezvous with a comet. In November, Rosetta’s mission is then to launch its Philae space probe to the comet which will provide the first analysis of a comet's composition by drilling into the surface. Rosetta is presently nearing the main asteroid belt between Jupiter and Mars. The spacecraft is still about 300,000 miles (500,000 km) from the comet, but in August the instruments will begin to map its surface in earnest.

Of these instruments, the NASA devices include:

MIRO, the Microwave Instrument for Rosetta Orbiter. Built in two parts, the microwave section of MIRO is designed to measure surface temperatures to provide information on the mechanisms that cause gas and dust to pull away from the surface of the comet to form the coma and tail. The other part, a spectrometer, will allow measurements of water, carbon monoxide, ammonia, and methanol in the gaseous coma of the comet.

Alice (which is not an acronym, but just a name that the instrument’s principal researcher, Alan Stern, liked) is a UV spectrometer designed to determine the gases present in the comet, and therefore gauge its history. For example, if Alice discovers neon gas, then the comet has not been heated to more than 16 K (-257º C or -430º F). If the neon appears to be part of the comet's original material the comet must have formed in an area of space colder than 16 K. Alice will also be used to measure the rate at which the comet releases water, carbon monoxide, and carbon dioxide, which will provide details of the surface composition of the nucleus.

IES, the Ion and Electron Sensor. One of five plasma analyzing instruments that make up the Rosetta Plasma Consortium (RPC) suite, the IES will measure the charged particles as the comet draws nearer to the sun and the solar wind increases.

During May and August, the Rosetta spacecraft will be executing a series of 10 orbit correction maneuvers (that is, thruster burns) to line itself up to meet comet 67P on 6 August. Rosetta will then continue to follow the comet around the Sun as it moves back out toward the orbit of Jupiter.

The lander, Philae, is planned for delivery to the comet’s surface in November 2014.

Sources: NASA/JPL, ESA

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