[X] My Assistant

[SigurRosFan]

Reporting today:

- http://spaceflightnow.com/news/n0604/04deepimpact/

--- Tempel 1 is usually a rather dim, weak comet with a water production rate of 16,000 tonnes per day. However, after the Deep Impact probe hit the comet this rate increased to 40,000 tonnes per day over the period 5-10 days after impact. Over the duration of the outburst, the total mass of water released by the impact was 250,000 tonnes. ---

[Bob Shaw]

This sounds like the dry(ish) comet hypothesis may also take a whacking...

Bob Shaw

[djellison]

laymans guestimate of implications....

DI spotted a lot of dusty material, and less water than was expected - but ground based obs show lots of water over time following the impact.

So - perhaps what we have is an object that was once a comparatively even mix of dust and ice, but the ice in the upper layers of the body slowly sublimes away under the influence of the warmth of the sun. However, the deeper the ice, the slower it can escape. This leaves the comet being more dust rich near the surface, and more ice rich toward the centre.

You whack it hard, and out flies a huge ammount of the dust, but what you also do is expose some of the more water rich material under the upper layers - so you get an initial outbusrt of dust, and then over the hours and days that follow, the exposed area returns to the dust rich balance near the surface as the sun warms the newly exposed material, forcing the higher water content to sublime out.

Maybe I'm a million miles from the mark, but it would seem to add up.

Doug

[Bob Shaw]

Doug:

Sounds reasonable - and all the more reason for a second flyby, if possible, so we can see the evolution of the crater. If the edges of the initial void have boiled away, then we might see Bruce's pet 'sun traps' in action, eroding the surface into strange non-impacty (you know what I mean!) shapes.

Bob Shaw

[Guest_PhilCo126_*]

Man, can't wait to see the photos of the impact area ... but it's a long wait untill the 2011 flyby

[ElkGroveDan]

250,000 tons of water, released by Deep Impact

And it's all landing on Northern California this week.

http://www.weather.com/weather/extended/US...cm_ite=CityPage

[ElkGroveDan]

So - perhaps what we have is an object that was once a comparatively even mix of dust and ice, but the ice in the upper layers of the body slowly sublimes away under the influence of the warmth of the sun.

I think you are spot on. This is the way snow works on Earth. Toward the end of the winter you will find snow fields and snow banks covered with dirt on top. Throughout the winter the particles of dust and dirt that fell with the snow were mixed evenly. As the snow sublimates the dirt gathers in a denser and denser layer on top. If you dig below you will see that the snow beneath it looks relatively clean. The effect will be exaggerated under trees or at the base of a hill where much more material mixes with the snow throughout the winter.

This is also one of the reasons cross-sections of glaciers seem to be striped. Waxing and waning warm seasons and varying snowfall levels allow the particulate matter to accumulate in layers that are either annual or multi-year cyclical.

In the more static environment of a comet there is only sublimating going on and no new snowfall. One can imagine that a crust of dust and other particles would build up on the surface over the eons, with clean ices beneath it.

[The Messenger]

Doug:

Sounds reasonable - and all the more reason for a second flyby, if possible, so we can see the evolution of the crater. If the edges of the initial void have boiled away, then we might see Bruce's pet 'sun traps' in action, eroding the surface into strange non-impacty (you know what I mean!) shapes.

Bob Shaw

Agreed, but only if the analysis holds water.

I am a nervous about the lack of a visual signature - this would be a more direct reading, than subtracting out variation in the solar wind flux. How do they know what the flux is, precisely at Tempel 1? Since the water was not found in more direct measurements - by Kleck, Hubble and others, (and it should have been), I would be all over the data reduction techniques used in the Swift analysis. I smell Dr. Von Eggle raising his ugly head

[Guest_BruceMoomaw_*]

It's always been assumed that this is how sublimation affects the surfaces of comets: the ice sublimates from the top layer, producing a crust of some sort, with the underlying ice later vaporizing in pockets immediately underneath it (especially since that black crust absorbs solar heat so well) and occasionally building up enough pressure to burst through it in jets.

The questions have always been (1) how deep the crust is (Mike A'Hearn pointed out in his early articles advocating the Deep Impact mission that estimates vary from 1 to 100 meters); and (2) whether it's loose powder or caked together into a crust with some degree of hardness. Given the violent and sporadic nature of cometary venting, the latter would seem more logical, unless there's a very deep layer of loose powder -- but, if http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1068.pdf is right, unfortunately the DI mission didn't even settle that question.

Probably the worst scientific loss from the failure of CONTOUR was the fact that it would have flown by one of the 3 fragments of Schwassmann-Wachmann 3 just this year, only a few years after that comet underwent enough of an internal pressure buildup to split into 3 fragments -- which would have given us a nice, very fresh cross-sectional look at the interior of a comet. The proposed CONTOUR 2 would also probably fly by a piece of SW-3 -- but 10-15 years later, by which time the Sun may have done God knows what to that nice exposed internal surface, or even caused all the fragments to crumble completely into little bits (as one of the three original fragments has already exploded into five still smaller ones). I wonder if that sort of internal pressure buildup doesn't require more layering than just an external crust of carbonaceous grit -- one thing DI did confirm is that solar heating also likely boils away still lower-temperature volatiles (such as ethane) from the ice immediately beneath the outer dark crust, leaving behind a layer of higher-temperature ices (water, methanol, HCN, etc.) When a comet is warmed enough, there are thus probably additional pockets of vaporized gas from the even colder innermost ices underneath that layer of less volatile ices, which serve as an additional pressure seal to keep in the internal gases until they reach a really high pressure level.

[The Messenger]

Check out the plots:

http://www.astrobio.net/news/modules.php?o...order=0&thold=0

I think they are dowsing.

That is not a limb I would crawl out on

[djellison]

The graph is a bit small, but whatever the values are, they go from between 5-10 as a baseline, to around 50 a few days later. Nothing particularly ambiguous about that.

Doug

[The Messenger]

[quote name=QUOTE REMOVED - un-needed when replying to it
[/quote]

Read the fine print. In order to establish the baseline, they measured the solar wind fluctuations in another part of the solar system and extrapolated, establishing what the baseline should be at the location of Tempel 1. The obvious and necessary sanity check here, would be to compare the result of this extrapolation with the estimates of the moisture content right after the impact. The two numbers do not agree, not even within one magnitude, so the most logical conclusion is that the extrapolation is not valid, not that every other observation was wrong.

Keep in mind that we all expected much more moisture - myself included, so it is natural to accept results that align with our preconceptions.

There is an argument in meteorlogical circles over whether or not last years record season is related to global warming. Many scientist, such as Gray of the USWB, insist the baseline has not shifted, and point out there were fewer than normal Pacific storms last year. It is rather myoptic to ignore the fact the poles are melting.