Scientists aren't sure how much, if any, of Comet ISON's nucleus survived a pass by the sun Thanksgiving Day, and that will likely mean the comet won't be visible in the night sky as had been hoped.
"There just doesn't seem to be enough left of the comet after its pass by the Sun," the Space Telescope Science Institute's Tracy Vogel wrote Sunday on the institute's ISON Blog.
The scientists plan to use the Hubble Space Telescope to get a closer look at the comet's nucleus, the ball of ice and dust from which its tails emanate, but that won't be possible for a few days as the comet moves away from the sun.
Because of the uncertainty over what actually happened to the comet on Thursday when it grazed the sun, it remains unclear whether it will shine brightly enough to be visible with the naked eye. If it does occur, it would likely be around Dec. 6-7, according to the observing campaign.
There is still much to learn from the comet, scientists said.