There is a comet currently approaching the inner solar system that has been generating a lot of interest since its discovery last year: comet C/2012 S1 (ISON).
ISON is a "sun grazer" comet, which means it will get unusually close to the sun. This is also ISON's first journey around the sun, and so it may have a lot of water and carbon-dioxide ice to burn off, which should create a lovely tail. Astronomers are very interested in observing ISON to gather more information on these types of comets, and we're all hoping that it will survive the journey around the sun to put on a spectacular display for us as it passes by Earth in December. However, before ISON gets close to Earth on its outbound swing, it gets even closer to Mars on its inbound journey.In August, ISON ought to be getting more active and developing its tail as it warms up, and astronomers want to get more information on this stage of the comet's development. Due to solar system geometry, ISON cannot be observed easily from Earth at this time - but it can be from Mars! In addition, we have a fabulous camera (HiRISE) and imaging spectrometer (CRISM) on the Mars Reconnaissance Orbiter in orbit at Mars. MRO is going to attempt to make measurements of ISON on August 20.
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This is clearly a complicated challenge, involving the HiRISE team, the CRISM team, and the spacecraft team all working together to get the timing and commands correct and to make sure that this sequence doesn't cause any harm to the spacecraft itself. We've done a few unusual observation campaigns before, including HiRISE observations of Mars' moons, Jupiter, and the Earth-Moon system (images can be found here: http://hirise.lpl.arizona.edu/releases/), so we're very hopeful that we can get successful measurements of comet ISON.
Even if the comet is not bright enough to get good images this time since it is still 93 million miles (150 million kilometers) away!, this will be good practice for a second observing campaign, including observations with more of the MRO instruments, as ISON passes by Mars at just 6.8 million miles (11 million kilometers) in late September and early October. Stay tuned!