Is Comet ISON a UFO? Hubble's scientists do a reality check

Image: Comet ISON
This is a close-up from a composite Hubble image that has been manipulated to show what appear to be three objects. They're actually three exposures of the same object: Comet ISON.

It's not at all certain that Comet ISON will turn out to be the "comet of the century," as hoped, but a couple of things are certain: It's not an alien spaceship, and it hasn't split up into three pieces.

Those were apparently questions on the minds of some folks last month, thanks to a flurry of videos and blog postings based on imagery from the Hubble Space Telescope's archives. The hoohah got hot enough to merit an official response, posted to the Space Telescope Science Institute's archive website and its ISON Blog.

It all started with a series of images captured by Hubble's Wide Field Camera 3 UVIS instrument on April 30. Various exposures were combined to produce a widely distributed color picture of Comet ISON against a background field of stars. When Internet sleuths took a close look at the archived image, it looked as if there were three separate objects hiding in the glare of ISON's coma.

Was ISON breaking up? Was the comet being escorted by two alien spacecraft? No. Just no.

Richard White, principal investigator for the Mikulski Archive for Space Telescopes, explained that the image was a composite, created by averaging the data from three separate camera exposures. The three objects are just different views of Comet ISON's nucleus.

"The comet itself does not have three pieces," White wrote. "They are an artifact from adding up the separate exposures. The comet does not look the same in each exposure because both the comet and the Hubble telescope are moving during the exposure. The comet is blurred, just as a picture taken out the window of a moving car will be blurred."

Check out the full explanation, and to get the latest prognostications on how bright Comet ISON will get in November, check in with the ISON Facebook page as well as the Comets Mailing List and the Twitter hashtag #ISON.

Image: Comet ISON in color
This is the image of Comet ISON that incorporates the three exposures from April 30 to produce a color image.

More about Comet ISON:

Alan Boyle is's science editor. Connect with the Cosmic Log community by "liking" the NBC News Science Facebook page, following @b0yle on Twitter and adding +Alan Boyle to your Google+ circles. To keep up with's stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.