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View Full Version : COMET ISON - Rare? Medium?, or Overdone?



Spacedude
2013-Jun-07, 02:56 PM
Like probably all of you I'm hoping for Rare. Looking at ISON's approach to the inner solar system it's interesting to see that it passes almost directly over Mars coming in and almost directly over the Earth heading out (assuming it survives grazing the sun of course). Our various assortment of cameras on and in orbit around Mars should have a good look at ISON as it whizzes overhead there by August. By then we should know how good of a show it will put on, at least coming in. I had read that as early as mid-July ISON should be close enough inbound to start melting water ice around the time it passes by the asteroid belt. Others may be cautious about ISON's performance due to past comet duds but I have a good feeling about this one. How about you?

antoniseb
2013-Jun-07, 04:08 PM
There have been a number of comet non-duds, and depending on which Hemisphere you live in they are memorable. I remember very well comets Hyakutake and Hale-Bopp. The first was a tiny comet that passed very close to Earth (closer than ISON will). The second was a giant comet that didn't get too close. Both of these were easily visible to the unaided eye far from the horizon. On the other hand I remember Ikeya-Seki was the comet of the Century, but because it was very bright only when near the Sun, my (at that time) untrained eye never saw it. It was a beautiful photographic object at Sunset.

So what will ISON be? Probably pretty good as comets go, but too subtle to make your friends suddenly love astronomy because of this AMAZING sight.

Spacedude
2013-Jun-07, 07:50 PM
I've been an avid comet watcher for about 50 years and the top performer for me was Comet Bennett back in 1970. I must have caught it at a perfect moment in time on that crisp clear spring pre-dawn morning. I estimated the head-to-tail length at at least 25 degrees and the tail appeared to flicker a bit, stars could be easily seen through the tail. I'm hoping for a repeat performance from ISON.

Swift
2013-Jun-07, 08:40 PM
CNN.com has a story about ISON today (http://edition.cnn.com/2013/06/07/us/comet-ison-5-things/index.html?hpt=hp_c4) (sort of an FAQ)

I thought this bit was funny:

"Predicting the behavior of comets is like predicting the behavior of cats -- can't really be done," Don Yeomans of NASA's Near-Earth Object Program told CNN.com in March.

And for those of you who worry:

What if ISON breaks apart? Is Earth in danger?

No. Experts say the comet won't threaten Earth. In fact, even if it breaks up, Battams says it could put on a big show.

KaiYeves
2013-Jun-07, 09:47 PM
Is it selfish to wish for ISON to be stunning because I was too young to remember Hale-Bopp or Hyakutake?

Hornblower
2013-Jun-07, 09:56 PM
A good example of a comet that exceeded expectations was Comet West of 1976. The nucleus shattered near perihelion and released a lot of dust in the process. If it ever returns it will be in the form of several lesser and widely separated comets.

Spacedude
2013-Jun-07, 10:30 PM
From what I've read about ISON it will experience 1 million degrees (F?) as it passes through the solar plasma while grazing around the sun and heads back in the Earth's direction. ISON will be at an approximate distance from the sun surface by about 1 solar diameter. At that temperature it seems that the surface of ISON would vaporize just about anything much less icy materials. At recent estimations of just 3-4 miles in "size" ISON will be put to the test with the double whammy of incredible heat and whiplash G forces. Looking forward to a double dipping comet for Thxgiving as it first passes by, and hopefully again at Xmas for a return visit......kinda like family :)

antoniseb
2013-Jun-07, 10:43 PM
From what I've read about ISON it will experience 1 million degrees (F?) as it passes through the solar plasma ...
The millions of degrees in the corona are kind of like millions of degrees of vacuum. There is next to no thermal inertia in the stuff it is going to pass through. The direct heating from the light and IR of the Sun will be a much bigger impact. Will THAT be enough to break ISON apart? No idea. As to the G forces, the comet will not experience any significant tidal forces breaking it up.

Spacedude
2013-Jun-08, 01:25 PM
Thanks for that clarification Antoniseb, I had wondered if reports of 1 million degrees of plasma exposure was as "real" as one might think. Do you know what the actual surface temperature of ISON might be at closest approach? Just judging by Mercury's sun facing temps in the 800F range ISON's should well exceed 1,000F. Good to hear too that the G-forces won't be too significant.

btw, I'd like to correct my previous post on the timing. ISON reaches the sun by Thxgiving (not by it's first pass by the Earth's orbit). Passing across the Earth's orbit will be closer to late Oct or Halloween as it heads towards the sun.

antoniseb
2013-Jun-08, 01:34 PM
... Do you know what the actual surface temperature of ISON might be at closest approach? Just judging by Mercury's sun facing temps in the 800F range ISON's should well exceed 1,000F. ...
*I* don't know what it will be, perhaps someone else here can venture an educated guess. The fact that ISON is rotating, and blowing off the highly heated surface material probably means that it won't get as hot as you might guess by comparing it to Mercury... beyond that I can't say.

Spacedude
2014-Feb-28, 04:02 PM
Just dusting off this old thread to answer my own question --- OVERDONE!

publiusr
2014-Feb-28, 09:58 PM
or rather, well done, seeing how close to the sun it got.

Best to pull a vanguard and say

OH WHAT A FLOPNIK

Superluminal
2014-Feb-28, 10:15 PM
It may have been a dud visually. But, we still got some interesting science from it.
http://www.astrobio.net/pressrelease/6034/a-rare-form-of-nitrogen-on-comet-ison