I wonder why no Tail? Doesn't the solar winds normally create the cometary tail? Must be something different about this comet's atmosphere.
![Confused :?](./images/smilies/icon_confused.gif)
Orin
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 wrote:I wonder why no Tail?
http://antwrp.gsfc.nasa.gov/apod/ap071029.htmlJohnD wrote:Second Comet Holmes APOD, 29th Oct.
See link to "sunglasses" in last line.
Is this a hack, or has APOD a GSoH?
John
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.mjmurraype wrote: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?
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.ta152h0 wrote:the bloody thing hit something. Bet you a an ice cold one. rare collisions does not imply no collisions. :P
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.Chris Peterson wrote: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.ta152h0 wrote:the bloody thing hit something. Bet you a an ice cold one. rare collisions does not imply no collisions.
orin stepanek wrote:http://antwrp.gsfc.nasa.gov/apod/ap071026.html
I wonder why no Tail?
I am wondering why it appears so symmetrical, circular evenCase wrote:As NASA's orbit diagram shows, the comet is approximately in opposition, so the tail will be mostly at the 'backside' of the comet.
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.MalcolmP wrote: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 ?
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 wrote: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
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.MalcolmP wrote: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 ??
Thanks, brill. explantion yes I see.Chris Peterson wrote: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...