Ah, now this was the beautiful view we were waiting for! When comet Siding Spring grazed past Mars last weekend, the robots hid while trying to sneak a peek. The first images of the comet's nucleus taken were historic, but it takes the Hubble Space Telescope to make it beautiful.
Top image: Composite of Siding Spring comet and Mars. Credit: NASA, ESA, PSI, JHU/APL, STScI/AURA
The image is a composite of several exposures. Hubble imaged the comet between 8:06 am on October 18th and 11:17 pm, and Mars at 10:37 pm on the 18th. The images are composited onto a background starfield from the Palomar Digital Sky Survey, with an angular separation of 1.5 arc minutes between the comet and planet during closest approach.
It had to be a composite, because a single exposure would've been a total mess. The fainter comet and stars would've been swamped by Mars' brightness, while their relative motions would have left them blurred.
Siding Spring is the first comet we've seen from the Oort Cloud, and this is our first chance to observe one up close and personal. Substantially less pretty but more scientifically interesting is this image of the comet from MAVEN, the new Martian satellite dedicated to watching gas concentrations and escape in the upper atmosphere.