23693Re: [comets-ml] 67P is a contact binary
- Jul 18, 2014From what i remember, the theory that explains striae is that time by time a larger fragment is released from nucleus (maybe few meters in size) then later it disintegrate to smaller and smaller pieces due casdading fragmentation. Or it is just larger dust that disintegrating to smaller and smaller pieces during it travel throughout tail.
On 07/18/2014 03:30 AM, David Seargent seargent@... [comets-ml] wrote:The striae in these large dust tails remind me very much of the similar features seen in the spray of water jets and even in drifting showers of rain. Does anyone know if there has been any work on the physics of these water-spray features? I guess that they are due to the breakup of larger water droplets and, if so, would tend to support the model of cometary striae as being due to similar disruption of larger tail particles rather than being caused directly by jets from the nucleus.
Date: Fri, 18 Jul 2014 10:17:12 +1000
Subject: Re: [comets-ml] 67P is a contact binary
Marshall thanks, for the links and thoughts.Does any have a good link that talks about Mcnaught and Panstarrs large striae features?I would like to understand if the rotational aspects can explain the synchronised deposit of material intothe bands. And how rotational momentum of this material make the tail widen over time.?I have some good images I will put some notes on to illustrate what I am trying to say here?regards, Alan
On Fri, Jul 18, 2014 at 3:13 AM, Marshall Eubanks tme@asteroidi nitiatives.com [comets-ml] <email@example.com> wrote:
On July 17, 2014 at 12:52 PM "Marshall Eubanks tme@... [comets-ml]" <firstname.lastname@example.org> wrote:Here is the DLR animation, which I don't think anyone has posted here :Looking at the video, I am not at all sure about this being a contact binary - I would expect a contact binary to be "nose to nose" and not side-by-side, from dynamical considerations. Both Toutatis and Itokawa appear to be nose-to-nose - see this image http://www.parabolicarc.com/tag/toutatis/ . I wonder if this shape for 67P couldn't be from erosion of a single body caused by heating during this comet's multiple passes by the Sun.Regards
On July 17, 2014 at 11:50 AM "Marshall Eubanks tme@... [comets-ml]" <email@example.com> wrote:
On July 17, 2014 at 5:49 AM "Alan Watson c2009a1@... [comets-ml]" <firstname.lastname@example.org> wrote:Gidday All,I was wondering if the shape of this comet could be explained by the effects of very long term cavitation, caused buy solar windSimilar to the effect seen on materials passing through continuous stream of fluids.The low density materials ejected from the comet due to the rotational momentum once free enough to roll off the surface.While the interstellar wind is fairly slow, the solar wind is fast all the way out the heliopause, order 400 km / sec. That is fast enough that(assuming there is no magnetic field on the comet) the Solar Wind protons come in at ~1 KeV, which tends to erode the surface, as it is energetic enough to breakmolecular bonds and ionize any atom it hits. This "sputtering" is thought to be a major cause the space weathering seen on small bodies throughout the solar system, and, on Europa (which has ice exposed to vacuum) there is evidence that it preferentially removes hydrogen from the surface, enriching the ice with oxygen.Of course, all of this would be very slow in the outer solar system (unless, like Europa, you happen to be in a planetary magnetosphere), but I would expect the result to be something more like sandblasting than moving material around on the surface.This has been studied a lot for asteroids, and in particular for Kuiper Belt Objects (which are more likely to be roughly equal binaries);Just thinking out aloud, could explain a lot of those peanut shape objects, but depends on rotational axis stability?
take a look at http://arxiv.org/abs/astro-ph/0504060
On Thu, Jul 17, 2014 at 12:42 PM, David Seargent seargent@... [comets-ml] <email@example.com> wrote:This is a very interesting object! The images remind me of the "balancing boulders" sometimes seen in rocky country. The background space can even be seen between the two nucleus components, except for a very small area around the point of contact.
The question is: Were these originally two unrelated comets that froze together following a very low-velocity collision in the Kuiper belt or was there initially a single nucleus which split (maybe after a meteorite impact?) and separated at such low velocity that the weak mutual gravitational attraction of the two fragments brought them back together again as a contact binary? The latter possibility seems the more likely, I think.
Either way, a minority of split comets may have started out as similar contact binaries. The most likely candidates are those which split into two nearly equal and enduring fragments. I recall that a backward computation of the orbits of two short-period comets (28P and 53P I think) revealed that these split apart from a single object over 100 years ago. That would seem to be a good candidate for a disrupted contact binary I think. Maybe 67P w ill also separate into two comets at some time in the future.
> To: firstname.lastname@example.org
> From: email@example.com
> Date: Tue, 15 Jul 2014 18:41:46 +0200
> Subject: [comets-ml] 67P is a contact binary
>> Hello all,
> this might be interesting for you
> Cheers, Maik
> If they give you ruled paper, write the other way. * Juan Ramon Jimenez
> http://www.comethunter.de * https://twitter.com/skymorph
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Kind regards, Alan Watson
--Kind regards, Alan Watson
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