Hubble spots Comet Siding Spring flying past Mars

Comet Siding Spring makes near miss of Mars in this image form the Hubble Space Telescope. Click to enlarge! Image Credit: NASA, ESA, PSI, JHU/APL, STScI/AURA 

Last Sunday the comet C/2013 A1  Siding Spring flew past Mars at a distance of just 140 thousand kilometers, or one third of the distance between the Earth and the Moon. It's the closest we've ever seen a comet get to a rocky planet- so close, in fact, that initial observations suggested it might even hit.

Data and observations are pouring in from the flotilla of orbiters around the Red Planet, and I'll certainly write more on this story as more results become available. For this blog post though I just want to show this amazing image, taken by the Hubble Space Telescope, showing Siding Spring at its closest point to Mars. Click on the image to zoom in.

This photo, which is defiantly now on my list of favourite space images, is actually a composite of two observations, one of Siding Spring and another of Mars. Although both objects would have fitted in the field of view of Wide Field Camera 3, the instrument used to obtain the image, Mars is around ten thousand times brighter than the comet. An exposure long enough to see any detail in Siding Spring would have captured Mars as just a shining white blob! A second problem that Siding Spring was moving across the sky much faster than Mars. Hubble had to track across the sky in time with it's motion, so a picture of Mars taken at the same time would have been a blur.

Photographic trickery aside, the result is incredible. I especially like the amount of detail on Mars, as well as the structure visible in Siding Spring's tail.

Much more on Siding Spring to come! Followed by the the main comet-related event of the year on 12th November, when the Rosetta spacecraft will send down a lander to make the first attempt at landing on a comet.

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