Deep Impact is not the only mission designed to study the composition of comets. Since the armada of spacecraft from Europe, Russia and Japan flew past comet Halley in 1986 and gave us our first view of a comet nucleus and direct measurements of gas and dust released from it, the ultimate goal has been to return samples of material to Earth from within a comet nucleus itself. This ambitious goal to obtain unaltered samples of material from the birth of the solar system is not yet within our reach but two current missions are designed to sample cometary material in very different ways.

Stardust:
The NASA Stardust spacecraft collected dust particles from comet Wild 2 during its 236 km flyby on 2 January 2004 and is now en route for a return to Earth in January 2006. The Open University provided sensors for the Dust Impact Monitor that detected almost 9000 dust particles impacting the bumper shield, seven of which penetrated the front shield but were not large enough to damage the spacecraft. These results predict that there are several thousand particles captured in the aerogel (an ultra low density porous glass) collectors for return to Earth. Some of these microscopic samples will be analysed in The Open University’s Planetary and Space Science Research Institute laboratories to investigate their composition and origin. This dust may be older than the solar system itself, revealing conditions that were present in the stars from which it originally formed.

Rosetta:
Rosetta is a European Space Agency mission which will make the first ever landing on the surface of a comet. It was launched on 2 March 2004 on a 10 year journey to comet Churyumov-Gerasimenko. It will arrive when the comet is far from the Sun and relatively inactive, to allow it to map the nucleus and release the lander, called Philae which will measure the composition and physical properties of the comet's surface and subsurface material. The orbiter, carrying 11 scientific instruments, will continue to study the evolution of the nucleus activity, and the surrounding dust, gas and magnetic fields, in unprecedented detail as the comet’s activity builds up during its approach to perihelion (closest approach to the Sun). The Open University is involved in the dust detector on the orbiter and three of Philae’s nine experiments, and leads the Ptolomy experiment to investigate the composition of ice sampled from below the surface.