November 29, 2013
ISON: Not Dead Yet?
by Tracy Vogel
Something seems to have survived ISON's encounter with the Sun ... but the question is what?
After fading in the sights of two NASA observatories and vanishing entirely from a third yesterday, astronomers speculated that ISON had met its demise. But then a faint smudge appeared in the images from the Solar and Heliospheric Observatory (SOHO). This could have been nothing more than a bit of leftover dust, but the fan-shaped feature didn't disperse, and began to brighten.
Observers at NASA's Comet ISON Observing Campaign have more analysis, but the gist is that no one is sure yet what, if anything, survived perihelion. It could be a fragment of ISON's nucleus. It could be too small to last more than a couple of days. Or there's a chance that it might have enough mass to grow back a tail and eventually appear in Earth's night sky.
We'll have to wait and see. HUBBLESITE
After fading in the sights of two NASA observatories and vanishing entirely from a third yesterday, astronomers speculated that ISON had met its demise. But then a faint smudge appeared in the images from the Solar and Heliospheric Observatory (SOHO). This could have been nothing more than a bit of leftover dust, but the fan-shaped feature didn't disperse, and began to brighten.
Observers at NASA's Comet ISON Observing Campaign have more analysis, but the gist is that no one is sure yet what, if anything, survived perihelion. It could be a fragment of ISON's nucleus. It could be too small to last more than a couple of days. Or there's a chance that it might have enough mass to grow back a tail and eventually appear in Earth's night sky.
We'll have to wait and see. HUBBLESITE
AND THEN GONE AGAIN NOW...
sadly as mere dust in the wind?
I close my eyes
Only for a moment and the moment's gone
All my dreams
Pass before my eyes with curiosity
Dust in the wind
All we are is dust in the wind
But in ISON's wake - a trail of questions! NASA Comet Ison Observing Campaign says:
Comet C/2012 S1 ISON in the Cor-2 images on the NASA STEREO Ahead spacecraft.
[Image credit: NRL/NASA]
Comet C/2012 S1 ISON in the Cor-2 images on the NASA STEREO Behind spacecraft.
[Image credit: NRL/NASA]
Pretty cool, huh?! Now I'm sure you have even more questions, and I promise we're almost there but first I want to be sure you understand what you're looking at here.
These images are "coronagraph" images, just like the SOHO/LASCO images we've been seeing, and the Sun is represented by that white circle in the center. But the spacecraft that took these images are in very different locations in space -- on the opposite side of the Sun, in fact! I recommend you check out this image that will show you exactly where the spacecraft were relative to the comet when these movies were made. (Keep in mind also that the SOHO spacecraft is close to Earth, so we have three unique views of ISON, which is just fabulous!) I also want to quickly note that these images have been processed to make them look "pretty", and have been rescaled, colorized and compressed. Thus these should not be used for robust scientific analysis -- you will need the actual "FITS" image data files for that. These are just a very beautiful look at a truly spectacular comet!
OK, Q and A time...
- What happened to comet ISON? Is it still alive? Great question, and we recommend you find a comet expert to answer that. ... [crickets] ... Sigh, OK I guess that's us. Well we don't have a very clear answer yet but there are a couple of things we can say for sure. First, during its passage through the Sun's million-degree corona, its dusty/gassy coma got very much burned away, though clearly some fine dust survived (which is the fine cloudy stuff you see being pushed away from the Sun). Second, something did emerge from the corona. It could be a comet, or just the remains of what once was. We can't tell right now.
- If there is a nucleus, how big is it?
There is no way we can tell this from the spacecraft data we have right now. We will need to wait for Hubble to be able to observe the comet, which will be in mid-to-late December, I believe. What I can tell you is that however big ISON's nucleus was a few weeks ago, it is much smaller now! - Will it be naked eye visible? When? How bright?
This is definitely the toughest question but also the most frequent. We still don't know if it will be naked eye but based on its current brightness in the LASCO images - which is around magnitude +5 and fading - it does seem unlikely that there will be much to see in the night sky. I suspect that some of the outstanding astrophotographers around the world will be able to get something, but I doubt it will be as spectacular as before perihelion. I hope I'm wrong though.I'd guess that a few observers will begin picking up ISON in a couple of days but if - and I do mean IF - comet ISON becomes naked eye visible, it won't be until near the end of next week (say, Dec 6 or 7). Please don't get your hopes up, but we all need to keep in mind how ISON keeps surprising us.
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But what about those seemingly unnoticed but evident monumental CME's in the images blasting away into our solar system? You wonder...
