Comet-chasing spacecraft to launch February 27th

On Friday morning at 0736 GMT, an Ariane 5 rocket is due to soar from French Guiana, launching ESA's Rosetta spacecraft on a daring mission to orbit, and land on, a comet.

Comets are building blocks of the outer solar system, virtually unchanged for 4.6 billion years. They hold key information to how the solar system formed. The mission is called Rosetta after the Rosetta stone which held key information to deciphering Egyptian hieroglyphics.

The mission will take 10 years to reach its target comet Churyumov-Gerasimenko (C-G for short), at 600 million km from the Sun (four times the Sun-Earth distance). Orbital speeds around comets are slow at centimetres per second, so the speed of the spacecraft needs to match the comet very precisely.

As the spacecraft orbits it will accompany the comet on its route towards the Sun, monitoring the development of the comet's tail and activity. Before the activity starts, a separate lander named Philae will detach from the spacecraft and land on the comet. The Philae obelisk was also a key in the understanding of hieroglyphics. Both orbiting and landing on a comet are space firsts and represent enormous technical challenges, with similarly huge scientific payoffs.

Dr Andrew Coates of MSSL-UCL is a co-investigator and science team lead for the Rosetta Plasma Consortium (RPC), a suite of 5 instruments on the orbiter. RPC is sensitive to plasma, the 4th state of matter after solid, liquid and gas, and will monitor the solar wind as it interacts with the comet to form the tail. "We are interested in how plasma affects the comet and how the comet affects the plasma in return. We should be able to measure properties of the nucleus like electrical conductivity and any magnetism present, as well as exploring the previously unknown environment within a few km of the nucleus. For us, the real excitement will be in 10-12 years but the long journey starts on Thursday" says Dr Coates.

RPC may be the first instrument to detect the comet's activity as it awakes from cosmic deep freeze approaching the Sun. Dr Coates is responsible for planning the comet operations science phase for RPC.

MSSL-UCL have a long interest in comets, they provided instrumentation for ESA's first comet mission which flew past comet Halley in 1996 and Grigg-Skjellerup in 1992. Giotto's two comets had a factor 100 difference in the production of gas, revealing important clues on how comet tails form. Over Rosetta's mission, C-G's production will change by a factor a million, giving much more information about how weak comets behave.