Europe’s Rosetta probe is back online after two and a half years of hibernation, and is now preparing to approach Comet Churyumov-Gerasimenko and land on its surface later this year.
The spacecraft is still many million kilometers away from its final target, but once it catches up, it will approach to within about 100 kilometers of the comet’s nucleus and select a suitable spot for the Philae lander to touch down. The plan is for Philae to anchor itself to the comet’s surface—a challenging feat, accomplished with the help of a harpoon—while Rosetta continues to orbit the comet and make measurements from a distance. If the gutsy landing maneuver succeeds, it will be the first landing on a comet.
Comet 67 P (also named for its discoverers, Ukrainian Klim Churyumov and Svetlana Gerasimenko of Tajikistan), has spent most of its life in the far reaches of our Solar System. But in 1840 its orbit brought it close to Jupiter, and the planet’s enormous gravitational pull changed the comet’s orbit Sun-ward. Its closest orbital approach to the Sun reduced to 1.29 AU (1 AU is the distance from the Sun to Earth), during which times it heats up and sprays dust and ice into space.
The scientific objectives of the Rosetta mission are to characterize the comet’s nucleus and topography and determine its chemical and mineralogical composition. Thermal, electrical and magnetic properties also will be measured, with a suite of instruments on both the orbiter and lander.
An instrument called Rosina (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) is probably of most interest to astrobiologists, because it will help us determine what the physical conditions were when comet Churyumov-Gerasimenko formed, and whether it even originated in our Solar System. The instrument can measure organic compounds within the comet, particularly amino acids, which scientists believe played a big role in the origin of life on Earth.
Another lander instrument whose results we’ll be watching closely is called COSAC (Cometary Sampling and Composition), which gathers information on the chemical composition of the comet’s surface. Even more exciting is that the lander has a drill, which can obtain cores down to a depth of about 20 cm (8 inches). The samples will be analyzed onboard the spacecraft, and data on their chemical and isotopic composition also will help us puzzle out where the comet came from.