Bad Astronomy

Comet ISON: Still Alive

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

That’s 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 Hubble’s keen eye:

Hubble Comet ISON
I spy with my Hubble eye a spry iceball. Click to hairystarenate.

Photo by NASA, ESA, and the Hubble Heritage Team (STScI/AURA)


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. We’ve seen that in images of other comets (including a dramatic one from Hubble back in 2006).

Comet 73P/Schwassmann-Wachmann losing its grip in 2006.

Photo by NASA, ESA, H. Weaver (JHU/APL), M. Mutchler and Z. Levay (STScI)


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 Sun’s 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; I’ve seen comets get to naked-eye visibility when this happens!


Or, it might not. As I’ve said before, comets are basically as predictable as cats. I wouldn’t bet either way.

Still, this latest Hubble image gives me hope this comet may yet brighten quite a bit. We’ll 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?)