Mars Express Observations During Comet Siding Spring Mars Encounter

Abstract:

The fly-by of Mars by Comet Siding Spring provides an absolutely unique opportunity both to study at close range an Oort Cloud comet, and to study from short distance and even in situ, the interaction of cometary gas and dust with a planetary atmosphere. Mars Express has been in orbit around Mars since December 2003 and the spacecraft and its instruments are still performing very well. After an initial worry about the safety of the spacecraft it has now been established that the risk for damage to the spacecraft is acceptable. A small phasing of the orbit was done in June in order to “hide” the spacecraft behind Mars during the time of the closest approach of the comet. Apart from that no special precautions are planned and a full set of observations of the comet and of Mars will be performed during the days around the closest approach. The cometary activity is being closely monitored and if new information of a possible increased risk appears, a safe spacecraft pointing and switching off non-essential instruments and sub-systems can be performed at a late stage.

The planned observations include imaging and taking spectral data of the comet nucleus and the coma, stellar occultation measurements through the coma, and observations of the Martian atmosphere and ionosphere. In situ observations of energetic particles and local plasma density measurements will be performed at several occasions and topside ionospheric sounding will be done. Detection of direct impacts on the spacecraft will be attempted as well as optical detection of meteor showers in the Martian atmosphere and remote observations of the hydrogen corona.

Mars Express instruments involved in the observations include HRSC, SpicaM, Omega, Aspera, MARSIS and PFS.