A numerical study of comet ISON near perihelion

The comet ISON has an extremely small perihelion distance (2.7 solar radii) and is also expected to have a very high production rate during its passage close to the sun in November of 2013. During that period, it is planned to be monitored by many ground- and space-based observatories, i.e. SOHO, STEREO, SDO, MRO, MESSENGER, SWIFT, Chandra, Spitzer, etc., all of which are able to provide substantial observational data of high quality about the comet and its interaction with the solar wind. In addition, as this sun-grazing comet penetrates so deep into the solar atmosphere, where the plasma environment is totally different from the normal solar wind conditions we are familiar with, it offers a great opportunity to study a new type of solar wind-comet interaction. Near perihelion, the photo-ionization time scale of the cometary neutrals is on the order of 100 s, which means that a large portion of neutrals are lost and most of the cometary ions are produced in a small region near the nucleus. Therefore, a much smaller upstream mass-loading region, a high production rate, a solar wind with a low Mach number and a strong interplanetary magnetic field together can dramatically alter the conventional cometary plasma environment of a bow shock, diamagnetic cavity and plasma tail. Preliminary results of a numerical study using the University of Michigan BATSRUS MHD model exploring the nature of the solar wind interaction and the coma environment are described. This work has been partially supported by grant AST-0707283 from the NSF Planetary Astronomy program and NASA Planetary Atmospheres program grant NNX09AB59G.