Comet Holmes in Outburst (APOD 26 Oct 2007)

[orin stepanek]

http://antwrp.gsfc.nasa.gov/apod/ap071026.html
I wonder why no Tail? Doesn't the solar winds normally create the cometary tail? Must be something different about this comet's atmosphere.
Orin

[Case]

I wonder why no Tail?

As NASA's orbit diagram shows, the comet is approximately in opposition, so the tail will be mostly at the 'backside' of the comet. This one might not get the long sideways pointing tail. Its distance from the sun is growing, so I think the tail should be shortening with time.

[orin stepanek]

Thanks Case; makes sense, I never considered that the orbit was so circular. It is more like the orbit of an asteroid than a comet.
Orin

[goredsox]

Apparently the comet is out by Jupiter right now. If this outburst is a tail viewed head-on from earth, it must be quite a sight from the side. Quick! Turn those Cassini cameras on it!!

[BMAONE23]

This is a JAVA driven webpage that shows the comet's orbital path and current respective location. It appears to be an asteroid belt comet.

http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=17P&orb=1

[JohnD]

Second Comet Holmes APOD, 29th Oct.

See link to "sunglasses" in last line.

Is this a hack, or has APOD a GSoH?

John

[orin stepanek]

Second Comet Holmes APOD, 29th Oct.

See link to "sunglasses" in last line.

Is this a hack, or has APOD a GSoH?

John

http://antwrp.gsfc.nasa.gov/apod/ap071029.html
Think it will get that bright? Nice song though!
Orin

[mjmurraype]

I know this is a long-shot, but is there any possibility that it increased in brightness due to a collision? Given that it orbits in the asteroid belt, surely this is a possibility?

[Chris Peterson]

I know this is a long-shot, but is there any possibility that it increased in brightness due to a collision? Given that it orbits in the asteroid belt, surely this is a possibility?

Of course it is possible, but I think in this case very unlikely. Collisions are rare in any case (even in the asteroid belt, where the density of objects is still extremely low), but since we know that this is at least the second time 17P/Holmes has undergone an outburst, it seems far more likely we are seeing something related to its structure or composition.

[ta152h0]

the bloody thing hit something. Bet you a an ice cold one. rare collisions does not imply no collisions.

[Chris Peterson]

the bloody thing hit something. Bet you a an ice cold one. rare collisions does not imply no collisions. :P

I don't know how to collect on that bet! But if hitting something at all is rare, doing so twice in a century is truly unlikely. And there are perfectly reasonable mechanisms that can explain outbursts like this without requiring any sort of collision.

[BMAONE23]

the bloody thing hit something. Bet you a an ice cold one. rare collisions does not imply no collisions.

I don't know how to collect on that bet! But if hitting something at all is rare, doing so twice in a century is truly unlikely. And there are perfectly reasonable mechanisms that can explain outbursts like this without requiring any sort of collision.

If it did collide with an asteroid, then it's orbit will be slightly changed, and since we have been observing it for more than 40 years (8 or so orbits) it should be relatively easy to determine if it was perturbed by an asteroidal collision event. Now, on the other hand, a meteroid impact might be a possible cause as well.

[Pete]

Think it will get that bright? Nice song though!
Orin

I hope it gets that bright! More likely it will eventually make its way to conjunction and get lost behind the Sun.

[ta152h0]

Which part of the pulverised rock would you follow the orbit of ? that decision could become crucial in the future if an object similar choses the earth as a target and future generations will have to deal with it.

[MalcolmP]

http://antwrp.gsfc.nasa.gov/apod/ap071026.html
I wonder why no Tail?

As NASA's orbit diagram shows, the comet is approximately in opposition, so the tail will be mostly at the 'backside' of the comet.

I am wondering why it appears so symmetrical, circular even
(although spaceweather.com calls it spherical, dunno how they know that in 3d !? )

I have read of various possibilities such as impact/collision and collapsing sink-holes/caverns but would that not require the coincidence of 'it' happening right up its 'backside' as we are viewing it ? If you see what I mean !
Would a 'side' impact still create such a circular cloud of debris ?

PS. The bad news was that I was looking at that area of the sky just the night before it all happened, nothing seen, then we had cloud and rain for several days , the good news is that it is now, finally, clear in SW England and I finally got to see the spectacle just a few days late

[Chris Peterson]

I am wondering why it appears so symmetrical, circular even
(although spaceweather.com calls it spherical, dunno how they know that in 3d !? )

I have read of various possibilities such as impact/collision and collapsing sink-holes/caverns but would that not require the coincidence of 'it' happening right up its 'backside' :-? as we are viewing it ? If you see what I mean !
Would a 'side' impact still create such a circular cloud of debris ?

A spherical cloud is what you would expect from ordinary diffusion. A high velocity impact would probably produce a directed debris stream. But some sort of surface collapse, or a low speed collision (as would be expected from co-orbiting debris) would simply release material at a low speed. The low speed, especially given a rotating nucleus, would favor a spherical cloud.

[Case]

we had cloud and rain for several days, the good news is that it is now, finally, clear in SW England and I finally got to see the spectacle just a few days late

First clear night since the news broke for me, too. Lovely sight! If friday is clear too, I might get a glimpse through a 30 cm (12") f/5 Newton.

[MalcolmP]

Chris : thanks for good explanation, I'm understanding your high vs. low speed impacts.
So far so good, but I still have a bit of a problem with the spherical theory,
if stuff is ejected (or diffuses out) at low speed it would still have the orbital velocity of the comet superimposed, so it should be ellipsoidal/sausage shaped, elongated fore and aft, but with a circular crossection as viewed from behind ?? or am I still not getting a grip on this thing ?
It is remarkably symmetric though for something that is not gravitationally bound, like a gas giant for example.

Perhaps another glass of beer might help me visualise

Case : Lucky you ! I am presently limited to 10x50 and 32x50 binos. my homemade 6" Newt is badly in need of realuminising
I'll keep my fingers and everything crossed for you for Friday !

[Chris Peterson]

So far so good, but I still have a bit of a problem with the spherical theory,
if stuff is ejected (or diffuses out) at low speed it would still have the orbital velocity of the comet superimposed, so it should be ellipsoidal/sausage shaped, elongated fore and aft, but with a circular crossection as viewed from behind ??

It is precisely because it carries the orbital velocity of the comet that the coma is spherical. If you take the center of the nucleus as your frame of reference, the particles move away from it in all directions but at a constant speed. Of course, the path of the nucleus is an ellipse, not a straight line, so given enough time you would expect material to be distributed along the orbit (each particle enters its own orbit, slightly faster or slower than the nucleus), but in the few days this comet has been outgassing, there hasn't been enough movement to show much asymmetry. But the nucleus does appear to be offset from the center of the coma, which may be related to its motion.

[ta152h0]

wonder if cASSINI can image this phenomenal object ?

[orin stepanek]

I wish a probe could be sent there. It would make a most interesting study. A lot could be learned from this comet.
Orin

[craterchains]

, , , , , , but, what made it get brighter?

OOOOO000000OOOOOO00OO0o0oo00

[orin stepanek]

, , , , , , but, what made it get brighter?

OOOOO000000OOOOOO00OO0o0oo00

Just maybe; that's one of the things we could learn.
Orin

[MalcolmP]

It is precisely because it carries the orbital velocity of the comet that the coma is spherical. If you take the center of the nucleus as your frame of reference, the particles move away from it in all directions but at a constant speed...

Thanks, brill. explantion yes I see.
/offers Chris a pint of homebrew beer

[JohnD]

Today's APOD (3/11/7) makes the point that the comet is receding, tail first, and happens to have the tail pointing directly away from Earth.

Many comets have two tails, one dust, the other plasma (?- electrically charged, anyway) that curves. If we can't see that curving tail, then Holmes doesn't have one. What does this tell us about Holmes?

JOhn