MAVEN remote sensing observations of Comet Siding Spring and its effects on Mars

The MAVEN spacecraft enters Mars orbit four weeks before Comet Siding Spring's passage by the planet. If orbit insertion and commissioning go according to plan, MAVEN is poised to make once-in-a-lifetime remote sensing observations of the comet and its effects on Mars. MAVEN's Imaging UltraViolet Spectrograph (IUVS) was designed to map emissions from common solar system gases and is therefore well suited to obtaining multispectral images of the comet at close range. IUVS's 115-340nm spectral range includes emissions from H, O, C, S, CO, CO2, and OH. The instrument includes the first interplanetary UV echelle which may be capable of measuring the D/H ratio given sufficient time on target. During IUVS's campaign on 17 October 2014, the comet's apparent size will increase 50% as it approaches.

MAVEN's truly unique opportunity is the search for potential changes in the atmosphere due to the comet. Since MAVEN was conceived to measure the atmosphere's response to changing solar influences, it is perfectly situated to detect atmospheric changes due to the deposition of gas, dust, energy and momentum from the comet. MAVEN will obtain the "before" picture by observing Mars for approximately two days pre-comet, and the "after" picture starting soon after its closest approach. IUVS's multiple observing modes each present an opportunity to detect atmospheric changes. First, limb scans of atmospheric emissions from 70 to 225 km altitude could detect new species, including metal ions from the dust, as well as detect changes in the atmospheric scale height due to heating by incoming cometary gas and dust. Second, scans of the extended atmospheric corona up to 4500 km altitude will be sensitive to atoms and molecules ejected or rebounding from atmospheric collisions, especially H, O and OH. Finally, multispectral imaging of the planet's disk might even detect "auroral"-type influences on the segment of the nightside directed into the comet flow. The primary limitation on MAVEN's sensitivity to these changes may be the timing of its safe return to operations after the passage of Siding Spring's debris cloud.