Examination of exosolar debris disk reveals unusual features

Ars Technica : The variable star AU Microscopii was discovered in the 1980s, and the Hubble Space Telescope later revealed that it was orbited by a disk of debris thought to be the remains of planetary material. The Hubble images revealed variations in the light passing through the debris, which suggested clumps of material that could be planets. Now, a team of researchers led by Anthony Boccaletti of the Paris Observatory used the new SPHERE instrument at the Very Large Telescope to study the disk more closely. The SPHERE images revealed even more clumps both closer and farther away from the star than were initially spotted. A reanalysis of the Hubble data revealed that the clumps have moved over the past few years at speeds reaching 4–10 km/s, with the outermost clumps moving fastest. The two farthest clumps appear to have speeds greater than AU Microscopii’s escape velocity. However, the fact that none of the other material in the disk is moving outward rules out the possibility that the clumps are driven by a stellar wind, and none of the other possible explanations have strong supporting evidence either.