The Microwave Instrument for Rosetta Orbiter, MIRO, a high-resolution spectrometer, has made the first detection of water vapour coming from comet 67P/Churyumov-Gerasimenko.

The result was submitted to the International Astronomical Union Central Bureau of Astronomical Telegrams, which is the official worldwide ‘clearinghouse’ for new discoveries.

Copied below is the electronic telegram (CBET 3912) circulated to subscribers of this service over the weekend:

S. Gulkis, Jet Propulsion Laboratory, California Institute of Technology, on behalf of the Microwave Instrument on Rosetta Orbiter (MIRO) science team, reports that the (1_10)-(1_01) water line at 556.9 GHz was first detected in Comet 67P/Churyumov-Gerasimenko with the MIRO instrument aboard the Rosetta spacecraft on June 6.55, 2014 UT. The line area is 0.39 +/-0.06 K km/s with the line amplitude of 0.48 +/-0.06 K and the line width of 0.76 +/-0.12 km/s. At the time of the observations, the spacecraft to comet distance was ~360,000 km and the heliocentric distance of the comet was 3.93 AU. An initial estimate of the water production rate based on the measurements is that it lies between 0.5 x 10^25 molecules/s and 4 x 10^25 molecules/s.

Water is a major volatile component of comets, along with carbon monoxide, methanol and ammonia. MIRO will help teach us about the abundance of each of these volatiles, in order to understand the nature of the comet’s nucleus, the process of outgassing and how the comet’s coma develops. Indeed, as Rosetta escorts 67P/C-G as it gets progressively closer to the Sun, MIRO will track the thermal evolution of the comet, providing important insights into the origins of outgassing regions on the surface of the comet.

This first estimate of the water production rate is within the range of models being used for comet 67P/C-G, and is excellent confirmation that MIRO is on target with its science goals. Needless to say, we’ll be keenly following how these numbers change over the course of the mission!