On December 18, 2013, the Hubble Space Telescope tried to observe Comet ISON one last time. As many people expected, there is no evidence of Comet ISON in these images.
The above image shows a composite of Hubble's observations. If there had been a feature that appeared in all of the images at the same place, that would have been very strong evidence of the comet. But all of the features in these images are not repeated at the same place from image to image. Nothing that appears in the images looks like a piece of a comet. Mostly what shows up are stars that are moving across the frame as the telescope tracks the comet's expected position, and a few galaxies, also trailed.
Other features are well-known artifacts produced within the camera, reflected and scattered light from brighter stars, and cosmic rays, which cause bright streaks across the images. Each of the four panels is a combination of two separate exposures. Had Comet ISON actually been present, it would have shown up in the same location in two or more of these frames.
These two images are composites of several exposures each, with Hubble pointing at two different ...