Round #2: Tempel 1

[CraigS]

Thought I'd start some excitement build-up for the second encounter with comet Tempel 1, this time by Stardust-NExT ….

NASA plans Valentine's date with a comet (http://www.physorg.com/news/2011-01-nasa-valentine-date-comet.html)



Should be interesting to get a close-up view of the impactor site.

Yep .. its all happening on February 14, folks !!

(I can't wait … I had a lot of fun with the Hartley 2 encounter … )

Cheers

[astroron]

Craig, yes it will be very interesting to see what the impactor crator looks like :question:
Cheers

[renormalised]

I think what the scientist need to realise is that each comet is a case all unto itself. Not every pile of rubble floating about out there is going to conform to the expected definition of what a comet is made of, how it's pieced together or even what it's history is. Tempel 1....is what it is. Until they find more comets just like it, they can only speculate as to what its origins and the derivation of its makeup are.

[CraigS]

Yep Carl …

Cool words.

After thinking through some of the questions posed by David Higgins recently, I'm starting to form a view that scientists' leaning towards classifying objects not yet understood, should come with a set of rules. The first rule would seems to be something like:

"Don't let the classification of an observed object become the primary driver for origin theory"

I mean, its hard to distinguish between, from either an origin, (or even a composition perspective), an Asteroid or a Comet, is it ?

Further, could I get away with saying that at the moment, the primary difference between a comet and an asteroid, is its orbit ?

Cheers

[renormalised]

The primary difference between a comet and an asteroid is their assumed points of origin and their general makeup. Asteroids....for the most part, have little or no free water in the form of ice. Some maybe chocka block full of water, but it's contained within their minerals. Comets have a large proportion of their structure made up of ices in various states of crud....from almost pure to thick mud :)

Quite a few asteroids have orbits very similar to comets....some probably are old comets that have completely de-iced and what you have left is the rocky bits hanging about in the old orbits.

[CraigS]

Yep. From our wrangling on Comets with certain folk, we dug fairly deeply into the spectroscopic technologies currently used to develop the picture pertaining to the composition of comets and asteroids.

Presently, there are holes in the infrared and near infrared arsenals, which (as usual), have resulted in:

- post-processing techniques (which mostly, have theoretical models underpinning them) and;
- in the case of Hartley-2, resulted in them sending one on the spacecraft, specifically designed to detect what we can't do directly from Earth based instruments. In the press releases, they actually stated that no Earth based spectrometer could have resulted in unambiguous confirmation of CO2 jets from the beastie.

There are debates presently raging about the veracity of the models and hence, the outcomes. (I think this may also be behind the Gliese 581g debate at the moment, as well).

What they need is a toe-cutter to sort 'em all out .. ;) :P :)

Cheers

[renormalised]

Think I should go in all guns blazing :):P

[sjastro]

I hope we don't have to go through that again.:bashcomp:

Regards

Steven

[CraigS]

I think there were detailed coffee shop discussions scheduled over the Xmas/NewYear period weren't there ??

I have expectations of new information, now.

Cheers

[sjastro]

Yes I believe they were going to rewrite the science of spectroscopy to get the right answer.:D

Regards

Steven

[renormalised]

Or would that be invent a completely new science...."electroplasmaspecology" :):P

[Rob_K]

What are Tempel 1 & Hartley 2?

"Thus, at the end of 2000, the ICQ adopted the practice of eliminating the suffixed numerals to comet names; this does mean, however, that permanent numbers or year/letter/number designations must be used with the name (of course, it is sufficient to use the permanent numbers or designations alone without the name, but not vice versa). The IAU adopted a policy of *optionally* including or excluding suffixed numerals to comet names when it approved the new set of comet-naming guidelines in March 2003. Thus, the Minor Planet Center and the Central Bureau for Astronomical Telegrams also no longer use comet-name suffixed numerals. (While a few people who have dealt a lot with comets over the last several decades will wish to continue using the redundant suffixed numerals for nostalgic reasons, such use will fade into oblivion during the next generation of astronomers -- so one might as well stop using them now and concentrate instead on the more logical prefixed numerals. This will make it easier on astronomers of the future, who will soon be wondering what the suffixed numerals stood for in the "old" literature, as the old suffixed numerals fall rapidly into dis-use.)"
http://www.cfa.harvard.edu/icq/cometnames.html

;)

NASA (pretty much alone) still uses the old designations, as well as a dying collection of crusty old comet observers & some new comet observers who want to sound like crusty old comet observers, but really the world has moved on! It was a lousy idea anyway, suited to a time when an astronomer might hope to only find a couple in a lifetime - LINEAR & NEAT killed this off!! :lol:

Tempel 1 tells you nothing. 9P (Tempel) tells you it was the 9th recognised short period comet, so it must have been early! :P

Cheers -

[CraigS]

Not long to go … should have some pictures about Tuesday night/Wednesday morning this week ?

Nasa JPL Stardust website here (http://stardustnext.jpl.nasa.gov/) ..
Images taken on Jan 18/19 16.3 and 15.8 mill miles here (http://stardustnext.jpl.nasa.gov/mission/comet_hunter_pr.html) ..

Looking forward to this.

Cheers

[higginsdj]

Or they have surface's that prevent contained ice from sublimating.....

In my view, there are only a certain number of formation mechanisms utilising only a limited number of compounds from a, universally speaking, small amount of space. As such, there should not be a great deal of difference between one comet and the next as there shouldn't be a great deal of difference between one asteroid and the next, though within the asteroids, there may be a mix of asteroids and 'dead' comets.

Of course 'great deal of difference' is relative. :)

Cheers

[higginsdj]

Yes.

No, by definition, a comet will exhibit a coma at some point during it's life, an asteroid won't. An Asteroid that suddenly displays a coma will be reclassified.

Typically, we can classify certain orbits to be comet like but as stated by others, we don't know enough about the origins and evolution to make such a call.

Cheers

[CraigS]

I guess there is one exception (so far) to this definition .. P/2010 A2.
They seem to have ended up classifying this as a binary asteroid because no gases were detected in the tail (via spectroscopic analysis), but it exhibited all the visual characteristics of a 'comet' (as I understand it), due to the debris in the tail.

Perhaps the gas part is now a differentiating factor, as a result of this (?)

Interesting …


Cheers

[higginsdj]

I would then argue that it wasn't a coma, just debris. By definition, a coma is the result of sublimation rather than impact.

Who has classified it as a Binary? Has a satellite been directly imaged or the presence of one uncovered photometrically or spectroscopically?

Cheers

[CraigS]

Hi David;

I referenced the reports in the How to Deflect an Asteroid (http://www.iceinspace.com.au/forum/showthread.php?t=71267) thread.
Here's the original David Jewitt et al report (http://arxiv.org/pdf/1010.2575v1) and here is the ESA report (http://arxiv.org/abs/1010.2883).

There were two papers written about it that I can find. I think one of them confirmed the binary nature. {EDIT: I stand corrected !! I don't think either of these said it was a binary … apologies for that !!}
The object was originally classified as a comet. The ESA Planck reports states:



This changed after their analysis.

Worthwhile reading the reports. (This thing is an oddball. I doubt that classification criteria would change because of it .. especially now that they've decided what it is).

Cheers

[higginsdj]

Yes, I think the conjecture was that some of the excavated material could settle into an orbit and acrete into a satellite but from the images a lot of it seems to have been blasted well out of range of being captured by the primary.

Cheers

[CraigS]

Yes David;

They say the parent body is likely to have been a rubble pile, too .

Cheers

[CraigS]

Ok folks, for the record:

Stardust Next Images here (http://stardustnext.jpl.nasa.gov/multimedia/tempel1_images.html).

Mission press conference here. (http://www.ustream.tv/recorded/12717282)

Notes from the press conference (by time on video) follow:

3:00 mins How do they get the trajectory correct ? "Its all done with MATH".
14:00 The impactor site has been spotted 150 m across with a mound in the centre. Ejecta fly up, and then came back down and settled (gravity). Conclusion is that the impact site was a weak, fragile, self-healing area.
16:55 About one dozen 1mm size impacts hit the spacecraft. About 5,000 smaller impacts. The impacts are bursty in nature, sounding like 'clods' , likened to flying through 'flak'. (Spacecraft approach velocity is 10.9km/sec - or about 24K mph)
18:51 Audio tape of the impacts.
19:50 Chemical analysis of spacecraft impact material: Carbon and Carbon-Nitrogen (CN).
21:30 Comet composition H2O ice (in part)
24:44 Observed smooth flows from subsurface volatile gas eruptions. Material flows downhill due to comet's own gravity.
26:08 Impactor site perimeter definition - size as expected, consistent with ejecta flying up and then resettling on the impact site.
27:07 Finally, they show the comparison of 2005 vs 2011. Oblique impact trajectory of 30% leaving crater of about 150 m across.
29:00 "Ejecta was all ice" - Schultz.

That's about the best I can get from it all.
The 'before' and 'after' impactor images will become available on the web shortly (not available at the time of writing this).


Cheers

[bartman]

Thanks for the summery and post Craig!
Cheers!
Bartman