• 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.



  • December 1, 2013

    ISON Hanging On


    So, something of Comet ISON has clearly survived its encounter with the Sun, but astronomers are still unsure exactly what made it -- a bit of the nucleus or a cloud of debris. This is where Hubble will come in. Once it's safely away from the Sun (Hubble cannot observe objects too close to the Sun, for fear of damaging its delicate optics) and in a good position to be viewed, around mid-December, Hubble will observe ISON to see if there's anything left of the nucleus.

    At this point, it's doubtful that ISON will be visible to the naked eye in the night sky. There just doesn't seem to be enough left of the comet after its pass by the Sun. ISON has surprised everyone before, though. If ISON were to become visible to the unaided eye, it would be around Dec. 6-7, according to the observers at NASA's Comet ISON Observing Campaign, whose blog has great, in-depth analysis of the latest news.

    Here's the lastest from NASA's Solar and Heliospheric Observatory, which has imagery through Dec. 1. Notice how whatever's left of ISON appears to be fading away at the conclusion.



    And here's the latest imagery from NASA's Solar Terrestrial Relations Observatory, which goes through Nov. 29.




  • November 29, 2013

    ISON: Not Dead Yet?

    Something seems to have survived ISON's encounter with the Sun ... but the question is what?

    After fading in the sights of two NASA observatories and vanishing entirely from a third yesterday, astronomers speculated that ISON had met its demise. But then a faint smudge appeared in the images from the Solar and Heliospheric Observatory (SOHO). This could have been nothing more than a bit of leftover dust, but the fan-shaped feature didn't disperse, and began to brighten.

    Observers at NASA's Comet ISON Observing Campaign have more analysis, but the gist is that no one is sure yet what, if anything, survived perihelion. It could be a fragment of ISON's nucleus. It could be too small to last more than a couple of days. Or there's a chance that it might have enough mass to grow back a tail and eventually appear in Earth's night sky. 

    We'll have to wait and see.