Instruments on the Rosetta spacecraft, which will be the first to orbit a comet and land a probe on its nucleus, have started transmitting data.
Rosetta currently is approaching the main asteroid belt located between Jupiter and Mars, still about 300,000 miles from the comet, and is due to arrive at comet 67P/Churyumov-Gerasimenko in August before landing a probe in November.
The European Space Agency (Esa) spacecraft is carrying three US instruments as part of a suite of 11 science instruments, which include the Microwave Instrument for Rosetta Orbiter (MIRO), an ultraviolet spectrometer called Alice, and the Ion and Electron Sensor (IES).
"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 (JPL) 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."
Alice will analyse gases in the comet's coma, which is the bright envelope of gas around the nucleus of the comet developed as a comet approaches the sun. Alice also will measure the rate at which the comet produces water, carbon monoxide and carbon dioxide. These measurements will provide valuable information about the surface composition of the nucleus.
MIRO is designed to provide data on how gas and dust leave the surface of the nucleus to form the coma and tail of the comet. Studying the surface temperature and evolution of the coma and tail provides information on how the comet evolves as it approaches and leaves the vicinity of the sun.
The instrument also will measure the amount of argon present, an important clue about the temperature of the solar system at the time the comet's nucleus originally formed more than 4.6 billion years ago.
IES is part of a suite of five instruments to analyse the plasma environment of the comet, particularly the coma. The instrument will measure the charged particles in the sun's outer atmosphere, or solar wind, as they interact with the gas flowing out from the comet while Rosetta is drawing nearer to the comet's nucleus.
NASA also provided part of the electronics package for the Double Focusing Mass Spectrometer, which is part of the Swiss-built Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument.
ROSINA will be the first instrument in space with sufficient resolution to be able to distinguish between molecular nitrogen and carbon monoxide, two molecules with approximately the same mass. Clear identification of nitrogen will help scientists understand conditions at the time the solar system was formed.