News story

Rosetta’s comet ‘sweats’ two glasses of water a second

67P is releasing the equivalent of two small glasses of water into space every second

First detection of water vapour
First detection of water vapour

Europe’s Rosetta spacecraft has found that comet 67P is releasing the equivalent of two small glasses of water into space every second, even at a cold 583 million kilometres from the Sun.

The first observations of water vapour streaming from the comet were made by the Microwave Instrument for Rosetta Orbiter, or MIRO, on 6 June, when the spacecraft was about 350 000 kilometres from the comet.

Since the initial detection, water vapour has been found every time MIRO has been pointed towards the comet.

First detection of water vapour
First detection of water vapour

Water is a major volatile component of comets, along with carbon monoxide, methanol and ammonia. MIRO is designed to help determine the abundance of each of these ingredients, in order to understand the nature of the comet’s nucleus, the process of outgassing and where they originate on the surface.

These gases stream away from the nucleus carrying dust, forming the comet’s surrounding ‘coma’. As the comet moves closer to the Sun, its coma will expand and, eventually, pressure from the solar wind will cause some of the material to stream out into a long tail.

Rosetta will be there to watch these developments up close. The comet – and Rosetta – will make its nearest approach to the Sun in August 2015, between the orbits of Earth and Mars.

Determining the changes in production rate of water vapour and other gases as the icy object moves around the Sun is important for comet science. But it is also vital for mission planning, because once Rosetta is closer to the comet, the outflow of gases may alter the craft’s trajectory.

Our comet is coming out of its deep-space slumber and beginning to put on a show for Rosetta’s science instruments,” says Matt Taylor, ESA’s Rosetta project scientist. “Rosetta’s engineers will also be using MIRO’s observations to help them plan for future mission events when we are operating close to the comet’s nucleus.

Today, the spacecraft is within 72 000 km of its destination. Six out of a total of ten rendezvous manoeuvres still need to be carried out to ensure that Rosetta arrives at a distance of just 100 km from the nucleus on 6 August.

UK involvement in Rosetta

Rosetta is a mission with significant UK involvement from industry and science.

One of the main challenges for all the companies designing instruments for Rosetta has been to ensure the components remain intact for ten years, while the spacecraft makes its way to the comet, and then work perfectly when it gets there. Not an easy task!

More about UK involvement in the mission can be found on our Rosetta page.

Published 1 July 2014