• December 4, 2013

    ISON: One Last Look?


    People are writing loving obituaries for Comet ISON, the sungrazer who lived life a little too close to the edge. Is that it? Are we ISON'ed out? In a post-ISON era? Adrift and alone in a universe bereft of ISONs?

    Probably, but Hubble is planning to do one more observation in late December, to try to get a glimpse of the remains.

    So what will it see? Well, possibly nothing. The pieces could be so small that they don't reflect light, or they could be slightly off the expected trajectory after breaking apart. (Hubble will have to follow the expected path unless Earth-bound observatories can help pinpoint the comet bits -- otherwise the telescope would just be guessing at a location.) Some people have wondered whether there's a danger from the fragments. The answer is no -- they still follow the general trajectory, and they're still extremely far away from Earth.

    Best case scenario, Hubble sees something like a coma, an expanding cloud of diffuse particles, or some bits of rubble that were once a nucleus.

    So there may be a little – very little – more ISON in your life sometime in the next several weeks. Hubble can't look right now -- the comet is still so close to the Sun that an observation would damage Hubble's optics. Hubble actually has safeguards that shut the telescope down if it tries to gaze at an object to close to the Sun. Ground observatories are also unable to view whatever's left of the comet at this point due to its location near the Sun -- by the time it would be in view, the sky is too bright.

    If Hubble does observe ISON, astronomers will be able to do things like estimate the size of the particles, and judge the speed at which the comet is disintegrating -- which will help us learn about ISON's composition and structure. Now, like a team of forensic examiners at the scene of the crime, it's time for astronomers look back on the data they've collected and figure out how and why ISON went to pieces, and what that means about Oort Cloud objects, sungrazers, and comets in general.