It has been an active summer for Rosetta’s comet. In August, 67P/Churyumov-Gerasimenko reached its perihelion (the closest point to the Sun), which led to a significant increase in surface activity.
In a new paper, soon to be published in Astronomy & Astrophysics, Rosetta scientists have discovered significant new features that appeared suddenly in the equatorial region of the comet's surface. The area is named after the Egyptian polymath Imhotep, and since last summer until May of this year, it has been a mostly smooth, dust-covered terrain.
In June, however, astronomers working with the probe data noticed the formation of a small circular feature. After a handful of days, the feature had expanded significantly, with a second feature also appearing. In a matter of weeks, the first feature had reached 220 meters (722 feet) in diameter, its companion 140 meters (459 feet) and a third feature had begun to appear alongside it. By the time Rosetta snapped the last picture used in the study on July 11, the three features had merged together and two more had started forming.
Annotated sequence of 10 images showing changes in the Imhotep region on Comet 67P/C-G. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
Dramatic changes are expected when a comet approaches the Sun. While 67P has shown incremental overall activity, the reason for the origin, structure and speed of the changes in these features remain unclear. Compared to theoretical models, the rate of erosion observed is significantly quicker. “These spectacular changes are proceeding extremely rapidly, with the rims of the features expanding by a few tens of centimetres per hour,” lead author Olivier Groussin said in a statement.
A few explanations have been put forward, but so far no conclusive evidence has been found, as the instruments on Rosetta haven’t identified any unusual gas or dust activity over the area. Being so close to the equator, the Imhotep region receives a substantial amount of sunlight; this could accelerate the release of larger particles, which are more difficult for Rosetta to detect.
Comet 67P continues to be a unique and fascinating object. We can expect more interesting science released by the Rosetta team in the next few months as data from the effect of the perihelion, which was on the 13th of August, are thoroughly analyzed.
Main image credit: Comet 67P on 19 September 2014 by ESA, via Flickr. CC BY-SA 2.0