73P/Schwassmann-Wachmann 3-B observed from the optical ground station

¹ Research and Scientific Support Department of ESA, ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands e-mail: tra-mi.ho@esa.int
² Science Payload and Advanced Concepts Office of ESA, ESTEC, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands
³ Sterrewacht Leiden, Nils Bohrweg 2, 2333 CA Leiden, The Netherlands

Received: 8 February 2007
Accepted: 17 September 2007

Abstract

Aims.In 2006 comet 73P/Schwassmann-Wachmann 3, which split in 1995 into five pieces, approached the Sun again with a swarm of new fragments. The same year in May, the conglomerate of sub-fragments from the original fragment B was observed with the S-Cam3 instrument mounted on the 1-m ESA Optical Ground Station (OGS) telescope in Tenerife, Spain. With a total FOV of ~876 km 730 km and a spatial resolution of ~73 km/pixel, the S-Cam3 observations provided the possibility to examine dust fragmentation processes, as well as dust and gas outflow, within the first few hundred kilometres of the sub-fragment surfaces.

Methods.The superconducting camera, S-Cam3, is an ultra-fast photon counting camera developed by ESA. Cooled to ~0.3 K, its sensitive superconducting tunnel junction sensors detect single photons, measuring their arrival time to accuracies of microseconds and determining its crude wavelength. The camera is also essentially noise-free except for sky background photons. Thus S-Cam3 essentially provides high-speed, low-resolution spectra between 395 nm and 1052 nm with a resolution of ~35 nm at 500 nm wavelength.

Results.The images acquired show three intensity maxima that were identified as most likely from the B fragment itself and two clusters of sub-fragments 253 km and 896 km away from fragment B. Furthermore we could see spatial intensity variations on short time scales (2–4 min), indicating the varying dust and gas emission of “subnuclei”. The gas and dust profiles do not show an inverse radial distribution () in all flow directions, but rather a clear deviation from a free radial outflow. This most likely is due to the gas outflow of one cluster of sub-fragments hitting the outflow of the other cluster. In other words, the material is expanding from one cluster into the other. In addition, the dust particles continue to fragment.