Comets may be just “dirty snowballs”, but they hold vital keys to unlocking the secrets of the processes at work during the formation of planets in our solar system that started about 4.6 billion years ago.
A spacecraft is speeding to a rendezvous with a comet where it is scheduled to perform several space exploration firsts: orbiting a comet, analysing the comet as it is drawn into a fiery encounter with the sun and – spectacularly – even landing a probe on to the comet’s surface.
It will study the comet at close range “as it transforms from a quiet nugget of ice and rock, frozen solid by years spent in deep space, to a sun-warmed dynamo spewing jets of gas and dust into a magnificently evolving tail”, says Dr Tony Phillips production editor of Nasa Science News.
This spacecraft is the European Space Agency’s Rosetta mission, with contributions from member states and the US space agency Nasa, and it is hurtling towards Comet 67P/ Churyumov-Gerasimenko that it is due to meet in August and to deploy its lander in November.
The craft is named after the inscribed stone tablet that was key to deciphering ancient Egyptian hieroglyphics, and scientists are hoping it will do the same for comet “language”. Its lander is named Philae after an island in the Nile River where an obelisk was found that helped decipher the Rosetta Stone.
The spacecraft was launched on its 11-year journey by an Ariane 5 rocket from Kourou in French Guiana in March 2004, and it flew past asteroids 2867 Steins (in 2008) and 21 Lutetia (in 2010) before entering deep space hibernation mode in June 2011. Then, with its destination in sight, it was “woken” on January 20 and its cameras were turned on.
“At first, the comet looked like “a dimensionless pinprick, inactive except for its quiet motion through space”, said Phillips. Then, on May 4, a bright cloud appeared around the nucleus.
“It’s beginning to look like a real comet,” said Holger Sierks of the Max Planck Institute for Solar System Research in Germany where Rosetta’s high-performance science camera was built.
Claudia Alexander, project scientist for the US Rosetta Project at Nasa’s Jet Propulsion Laboratory in California, said the comet was “coming alive – and it’s even more active than I expected”.
The spacecraft is carrying 11 scientific instruments to probe the comet’s nucleus – estimated to be 4km across – and to map its surface in fine detail. The lander is carrying instruments to study what is described as “some of the most primitive, unprocessed material in the solar system”.
Comet fly-bys to collect data have been performed on several occasions, but Rosetta is expected to do a lot more.
In particular, it will track the comet and examine its behaviour before, during and after perihelion – the point in the comet’s orbit at which it is nearest the sun – before finally shutting down at the end of next year.
“A fly-by is just a tantalising glimpse of a comet at one stage in its evolution. Rosetta is different,” Alexander said. “It will orbit 67P for 17 months. We’ll see this comet evolve right before our eyes as we accompany it towards the sun and back out again.”
The lander will anchor itself to the comet’s surface with harpoons to counter the lack of gravity. “The feet may drill into something crunchy like permafrost, or maybe into something rock solid,” he said. - Cape Argus
The Rosetta Stone is a rock tablet inscribed with a decree issued at Memphis in 196 BCE on behalf of King Ptolemy V.
The decree appears in three scripts: the upper text is Ancient Egyptian hieroglyphs, the middle portion Demotic script, and the lowest Ancient Greek.
Because it presents essentially the same text in all three scripts (with some minor differences), it provided the key to the modern understanding of Egyptian hieroglyphs.
Although it is believed to have originally been displayed within a temple, the 114cm high and 72cm wide stone was probably moved and was eventually used as building material in the construction of Fort Julien near the town of Rashid (Rosetta) in the Nile Delta.
It was rediscovered in 1799 by a soldier, Pierre-François Bouchard, serving in the Napoleonic expedition to Egypt.
l Source - Wikipedia
Key dates of the Rosetta mission:
l Launch – March 2, 2004
l First Earth gravity assist – March 4, 2005
l Mars gravity assist – February 25, 2007
l Second Earth gravity assist – November 13, 2007
l Asteroid Steins fly-by – September 5, 2008
l Third Earth gravity assist – November 13, 2009
l Asteroid Lutetia fly-by – July 10, 2010
l Enter deep space hibernation mode – June 8, 2011
l Exit deep space hibernation – January 20, 2014
l Rendezvous manoeuvre – May 2014
l Arrive at comet – August 2014
l Start global mapping – August 2014
l Lander delivery – November 2014
l End of mission – December 31, 2015