February 23, 2004. Copyright 2002. Graphic News. All rights reserved.

Ten-year journey to catch a comet

LONDON, February 23, Graphic News: Scientists are anxiously awaiting the launch of a pioneering spacecraft designed to look back 4.6 billion years to an epoch before planets existed, when only a vast swarm of asteroids and comets surrounded the Sun.

The European Space AgencyÕs 892 million euro (US$1.1 billion, £600 million) Rosetta will bounce around the solar system like a cosmic billiard ball to catch up with the nucleus of a comet. Once in orbit it will land a washing machine-sized robot on the cometÕs icy surface to observe the changes that occur in activity as the nucleus hurtles towards the sun.

After being delayed for more than a year, Rosetta is due to blast off on Thursday (February 26) at 07:16GMT (2:16 am EST) atop  a Ariane 5 rocket from Kourou in French Guiana for its rendezvous with Comet 67P/Churyumov-Gerasimenko (67P/C-G). 

Named after the Rosetta Stone, the key which enabled linguists to discover the secrets of ancient Egypt by deciphering hieroglyphics for the first time, it is expected that the modern Rosetta will prove instrumental in unravelling an even older mystery, the birth of the solar system. 

Because these primordial leftovers were never subject to the kinds of thermal and chemical change that happened during the formation of the planets, comets are, in a sense, time capsules that can be used to find out more about conditions in the early solar system.

These Òdirty snowballsÓ may also be able to answer specific questions about the early history of the Earth. For example, some scientists suggest that much of the water in the EarthÕs oceans, and the original gases in its atmosphere before life got to work on them, were ÒplasteredÓ on to the planet by collisions with comets, rather than emerging from its interior through volcanic vents. If the water found on comets contains an Earth-like ratio of deuterium (a form of hydrogen that has a heavy nucleus) to ordinary, light hydrogen, that would favour the plastering theory. 

A more intriguing area that this mission is meant to cast light on is the origin of life -- or, rather, the chemical precursors of life. Comets contain amino acids, which are the building-blocks of proteins. If comets ever did contribute to the EarthÕs oceans, they may have brought part of the complex carbon-based chemistry of life with them. RosettaÕs Cometary Sampling and Composition experiment, which will analyse dust for carbon-based molecules, may indicate that life on Earth is indeed a legacy of the stars. 

The spacecraft consists of two main components, a box-like orbiter carrying communications, solar arrays, propulsion systems and payload of 11 scientific instruments, plus a nifty 100kg lander named Philae.

Rosetta will weigh a chunky 2.9 tonnes at launch, with over 50% of the mass being onboard propellant to keep the spacecraft moving throughout its 10-year mission, particularly during the delicate and complex manoeuvres in orbit around the comet nucleus.

As a result, ESA will use EuropeÕs most powerful launcher, the Ariane 5, to boost Rosetta towards its destination. Even then the flight will also require a gravity-assist flyby of Mars in 2007 and three similar flybys of Earth in 2005, 2007 and 2009, to put Rosetta on track for rendezvous with 67P/C-G in May 2014. En route, Rosetta will wake from its hybernation to study two asteroids at close range.

On reaching the comet, Rosetta will first match velocities, and then drift along carrying out observations. Once in orbit, mission control will refine the course of the spacecraft using images sent back by the probe to move Rosetta as close as 2km (1.2 miles) above the nucleus, to provide the most detailed views yet obtained of a comet. 

In November 2014, once detailed mapping has been completed and a landing site selected, Rosetta will release the lander which will descend onto the surface and secure itself in position against the cometÕs feeble gravity using a harpoon fired into the surface. 

The lander will operate for at least a month, transmitting its data back to Earth via the orbiter which will continue to observe the comet until the expected end of its mission in December 2015.
/ENDS

Source: European Space Agency