The photographic proof is in: Reports of Comet ISON’s demise were greatly exaggerated. Contrary to some pessimistic predictions, new Hubble data show the comet still trucking along as it falls inward of Mars and ever closer toward the Sun.
This new image, recorded by Hubble on October 9, combines long exposures taken through blue and red filters. Over 29 minutes, Hubble switched back and forth between these filters as it tracked Comet ISON across the sky.
What little color ISON has is due to differences between a comet’s coma and its tail. The tail, comprised of dust particles torn away from the comet by the gentle pressure of sunlight, appears redder because dust grains reflect redder light. The coma, by contrast, is bluer. It doesn’t contain much dust, just gas sublimating from the comet’s surface.
The comet’s nucleus, estimated at less than 2 kilometers in diameter, is tiny even through Hubble’s eagle eyes. A single pixel in this image spans 55 km of comet, making the nucleus un-resolvable at this separation (about twice the Earth-Sun distance). Still, careful study of this image suggests the nucleus is almost certainly still intact — the coma spreads out evenly from a single point, ...