What happens to ISON's remains?

Apologies for going quiet on this site - it takes a while to recover from events like this! I have actually started several blog posts and then never gotten chance to finish them. That will happen eventually, and I'll post new content on here from time to time, but right now I just want to address this one issue that I'm still getting an email bombardment about: what happens now to comet ISON's remains?

As we all know, comet ISON is no more. It clearly fell apart in the hours surrounding its close brush with the Sun and now exists simple as a dusty cloud and some warm fuzzy memories. But what of that dusty cloud? What if there are chunks remaining? Where are they going? Will they change course and hit Earth? Is Earth going to pass through ISON's remains? Are we doomed?!!

These are all variations on several questions I've been receiving, so let me clear up some of these, and hopefully allay the concerns of a few people.

As comets travel through space they leave behind themselves a huge trail of tiny dust that can be millions of miles long. Our solar system was already full of them and now, thanks to ISON, it has another one. Now, I have not actually seen any professionally made orbit simulations but, from what I understand, there's a chance that in mid-January of 2014, Earth might pass through, or close to, part of comet ISON's dust trail. So, time to panic? NO! And here are three good reasons why:
  • Reason #1: Any dust that was released from comet ISON will be tiny. We're talking about sand-grains here. And what happens when a sand-grain sized rock hits Earth's atmosphere? It burns up at extremely high altitude, and we get to see a shooting star in the sky! How many will we see? Well that brings me nicely to...
  • Reason #2: Space is B-I-G and empty, and so are comet tails. If you were a typical dust grain in a comet's tail, within a few hours of being released you would be well separated from your sibling dust grains and within a few days, you may find yourself hundreds or even thousands of miles from your nearest neighbor. When we talk about a region of space being dusty, we mean it's dusty as opposed to being a complete vacuous void. It's not dusty like an old abandoned warehouse, or one of those construction trucks that drops chunks on the highway that crack your windshield. Instead, think of ISON's tail like a stream of smoke. At the source it might be relatively dense, but very quickly it diffuses and becomes so thin that you can barely notice it. That's what we would have with any dust trail left behind ISON. Not only would the dust be tiny and harmless, there's very little of it! But if that isn't enough to convince you...
  • Reason #3: When was the last time Earth passed through the tail of a comet? A centuries years ago? A few years maybe? Nope. How about last weekend! That's right, we just had the annual Geminid meteor shower, and this year it was a pretty good show! The Geminids are believed to be the resulting trail from the asteroid comet space-rock 3200 Phaeton. If you check out Wikipedia you can find a complete list of meteor showers that Earth experiences, all of which are the result of passing through comet tails and debris trails in space.
So the takeaway message here is that there's apparently a chance that in mid-January, Earth might encounter a handful of sand-grains that are substantially fewer in number than it encounters on one of a couple of dozen occasions throughout the year. Terrifying, right?

OK, now on to the second part, which is much shorter. I've read concerns from folks who are worried that now ISON has fallen apart, there could be a whole load of comet chunks flying off in all directions. That's simply not true. Any larger (centimeter? meter?) chunks of rubble remaining from comet ISON will continue along in the same orbit that we knew the comet would follow - namely, harmlessly right out of the solar system. (That aforementioned dust trail I just talked about refers only to stuff that was released by ISON before it got vaporized.)

We are safe, I promise! I just paid all my bills for the month. Believe me, if I thought the apocalypse was around the corner, I'd be sitting somewhere hot and sandy with a beer in my hand right now instead of blogging and reaching for another mug of mediocre coffee!

Keep up-to-date on the latest ISON and sungrazing comet news via my @SungrazerComets Twitter feed. All opinions stated on there, and in these blog posts, are my own, and not necessarily those of NASA or the Naval Research Lab.