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SYFY WIRE Bad Astronomy

Comet ISON: Still Alive

By Phil Plait

As of Oct. 9, 2013, comet C/2012 S1 (ISON) is still alive.

Thatâs the verdict from a Hubble Space Telescope image taken on that day. At a distance of 280 million kilometers (175 million miles), the comet presented a fine sight to Hubbleâs keen eye:

There has been some speculation that this comet may disintegrate as it gets near the Sun in late November. Comets are basically dirty snowballs; ice, rock, and gravel mixed together. As the comet warms, the ice turns into a gas, creating the fuzzy head around the solid nucleus, and the long tail that streams away due to the solar wind and pressure from fierce sunlight. If enough of the ice goes away, the comet loses structural integrity and can fall apart. Weâve seen that in images of other comets (including a dramatic one from Hubble back in 2006).

The thing to note is that the head of Comet ISON, the tiny fuzzy part at the bottom left, appears intact. If the comet were breaking up, we should see tiny pieces trailing behind it. The image looks clean, so it seems to me this comet still has some sizzle left to go.

ISON is on an orbit that will take it deep into the solar system, practically scraping the Sunâs surface, missing it by only a million kilometers (700,000 miles or so), less than the diameter of the Sun itself. Because it will be so close to the Sun, ISON could get very bright; Iâve seen comets get to naked-eye visibility when this happens!

Or, it might not. As Iâve said before, comets are basically as predictable as cats. I wouldnât bet either way.

Still, this latest Hubble image gives me hope this comet may yet brighten quite a bit. Weâll see. If you want to observe it yourself, star charts are available online. I plan on taking a look soon myself. Good comets are rare beasts, and I want to make sure I take every chance I get to see one.

Previous posts about ISON:

What the Heck Is Comet ISON Doing?
Hubble Spies a Surprisingly Active Comet ISON
Comet ISON Among the Sparkling Stars
WWCID? (What Will Comet ISON Do?)

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