Click on the image for the full animation
This two-image blink shows a comparison of two exposure times in images from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity showing comet C/2013 A1 Siding Spring as it flew near Mars on Oct. 19, 2014.
The images were taken about two-and-a-half hours before the closest approach of the comet's nucleus to Mars, with exposure durations of 50 seconds and 10 seconds. The sky was still relatively dark, before Martian dawn. At the time of closest approach, the morning sky was too bright for observation of the comet.
The images have been processed by removal of detector artifacts and slight twilight glow. The duration of the exposure resulted in a 2.5-pixel smear from rotation of Mars.
A Martian dust storm to the west of Opportunity hampered visibility somewhat on Oct. 19, compared to the sky over Opportunity a week earlier.
For more information about comet Siding Spring, see http://mars.nasa.gov/comets/sidingspring/.