After travelling a distance of 6.4 billion kilometres since it was launched in March 2004, Rosetta made space history on August 6 when it became the first spacecraft to rendezvous with a comet — 67P/Churyumov-Gerasimenko, a 4.5-km-long object. The craft, which is at an altitude of about 100 km, will in the next couple of months move closer to 67P till it is about 4 km above its surface. At this altitude, the next biggest challenge will be to ensure that the lander, Philae, to be airdropped from Rosetta, lands safely on the comet. The identification of a smooth landing site to deploy the lander in November was not done in advance as little information was available about the nature of the terrain. Images collected by the craft from a distance of 285 km from the comet have suggested a ragged surface marked by “sharp-edged structures” with precipitous cliffs. It remains to be seen if the “smooth” areas seen from that height are indeed smooth when better-resolution pictures become available as the Rosetta gets closer. Unlike the Curiosity rover that is moving freely on Mars, Philae, with an array of instruments, would be anchored to the surface. Rosetta has already changed our understanding of 67P’s shape — it appears as a “double-lobed structure” with a neck connecting the two. It could have either been formed by the fusion of two comets or by differential erosion at the spot that now forms the neck.
Comets are primitive objects formed from debris left over when the Solar System was formed around 4.6 billion years ago. They retain primordial secrets — the gas, dust and organic molecules since they were created. Hence, information garnered from 67P can unlock many secrets about the birth and evolution of the Solar System and the origin of water and life on Earth. It is believed that comets had seeded Earth with water and carbon-containing molecules, particularly amino acids that are the building blocks of life. By studying materials lying 20 cm below the comet’s surface, Philae is expected to provide vital information about organic materials that are securely locked and cannot be studied from Earth. Since life on earth is comprised exclusively of left-handed amino acids, the “predominance” of such molecules in 67P would strengthen the possibility of comets’ role in seeding life on the planet of humans. Another important study is the assessment of the ratio of normal to heavy water (where one of the two normal hydrogen atoms has been replaced by the heavy hydrogen isotope deuterium) to ascertain if the comet’s ice signature matches that of water on Earth. A few years ago, the Hartley 2 comet was found to have the same signature as water; none of the other comets studied before had a similar match.