ESA`s space probe to reveal mysteries of comets

ESA`s space probe Rosetta, which is supposed to rendezvous, next spring, with comet Churyumov-Gerasimenko, is set to reveal many mysteries about comets.

Washington: ESA`s space probe Rosetta, which is supposed to rendezvous, next spring, with comet Churyumov-Gerasimenko, is set to reveal many mysteries about comets.

On its way toward the Sun comet Churyumov-Gerasimenko, next year`s destination of ESA`s spacecraft Rosetta, will start emitting gas and dust earlier than previously expected.

The comet`s activity should be measurable from Earth by March 2014. This is one of the results of a new study performed by a group of researchers under the lead of the Max Planck Institute for Solar System Research (MPS) in Germany.

The scientists analyzed numerous images from the comet`s past three orbits around the Sun, obtained with ground based telescopes. For the first time, they were able to reconstruct the comet`s activity in all phases of its orbit.

A comet spends the main part of its existence far from the Sun as an unchanged lump of ice and rock. When it approaches the Sun, however, a metamorphosis takes place: highly volatile substances vaporize from the nucleus carrying fountains of dust particles with them.

These accumulate to form the comet`s atmosphere, the coma, and are the origin of its tail, a comet`s most characteristic feature. However, the principles governing these processes are still only poorly understood. What instances spark the ejection of gas and dust? How does this activity evolve? And which processes on the surface and within the comet`s nucleus are decisive?

Next year, ESA`s spacecraft Rosetta will try to answer these questions. The space probe is scheduled to rendezvous with comet Churyumov-Gerasimenko in spring, deposit a lander on its surface in the autumn of 2014, and accompany the comet on its way toward the Sun.

The mission therefore offers the unique chance to study all phases of the onset of cometary activity from close-up. The new results presented by researchers from the MPS now suggest that Churyumov-Gerasimenko could allow for exciting insights very early in the course of the mission.

The scientists base their predictions on 31 data sets recorded by them and other professional groups in the years between 1995 and 2010 with telescopes like the Very Large Telescope (VLT) at the European Southern Observatory (ESO). The images show the comet at different points during its orbit and thus in different phases of activity.

In their new study the researchers were able to analyze data that had been unusable before. Key to this success was a method usually employed to discover exoplanets in these crowded star fields. Images taken shortly after one another are subtracted making the crowded starry background disappear and revealing bodies that -- like a comet -- change their position. After using this technique to make the comet stand out from the camouflage of background stars, its brightness could be accurately measured.

The elaborate calculations rendered astonishing news: to the researchers` surprise the comet`s brightness increased distinctly at a distance of 4.3 astronomical units from the Sun.

This is 4.3 times the distance between the Sun and Earth. Before, it had been thought a rule of thumb, that comets become active at a distance of approximately 3 astronomical units. At this distance the Sun heats the comet`s surface enough for water ice to sublimate.