[meteorite-list] What Happens to Comet ISON's Remains?

[Ron Baalke]

http://www.isoncampaign.org/karl/what-happens-to-isons-remains

What happens to ISON's remains?
by Karl Battams 
NASA Comet ISON Observing Campaign
December 18, 2013

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!