Thanks ToSeek,

You better change your name in ToFind (or ToFound)

This is a remarkable change of tone to previous press releases, I don't see too many differences between comet Borrelly, Wild 2 and Tempel 1. A good thing is that the dirty snowball model can be laid to rest (even the snowy dirtball is out when the dust to ice ratio is in favor of dust), but I'm not sure I agree with the new picture of a comet with less density than a snowbank, possibly without a core????

Then how can we explain all the topological features? How can the features on Wild 2 be explained, I just don't buy all this "fluffiness".

I also wonder on what A'Hearn is basing the idea that the interior is totally different from the surface; did he see any of the subsurface?

And I didn't see any mention of the "bright patches", I'm curious what kind of "fluff' produces those patches.

Cheers.

This is becoming a

It is interesting that the craters on Wild 2 are not thought by this team to be impact craters...

This second article (overview of conclusions, not detailed observations yet) DID say that there was spectral evidence for subsurface water in the impact.

They haven't said anything about how they have come to the conclusion about the density, but the only way they could be sure would be if they were able to measure accurately the gravitational influence of the comet nucleus on the spacecraft (impact or flyby).

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Ok, we had a "dirty snowball" model, then a "snowy dirtball" model, is this the start of a "fluffy no-ball" model?

There already was evidence of water molecules, there just wasn't any increase (maybe even a decrease) on impact, just a humungous amount of dust; that's why the surface "must be" dusty (or fluffy). It begs the question how jets can form on comets, a large amount of fluff could never account for highly collimated jets, ubiquitous on comets. I wonder what happens to the need for subsurface ice/volatiles, if the "snowball" model is abandoned what can produce the dusty jets?

Cheers.

How about a potato covered with dust? Or according to O'Hearn, a potato full of fine dust and crystaline water?

I've missed you guys! and just because I started to sound too much like Hoagland and got myself BANNED, doesn't give you an excuse to take off your THINKING CAPS.

As V- has stated, it is difficult to imagine how a pile of fluffy, snowy dust could form inside an object shape, complete with craters.

O'Hearn questions whether or not they are craters, because we have not seen craters on other comets. Invalid argument - we haven't looked at any quite this closely. What are they? Eyes? I've seen a lot of potatoes covered with dust, but not one potato filled with finely ground silicates. How would fine dust get inside of anything?????

A better explaination MIGHT be, the probe struck a resilient dusty, icy surface, creating the initial hot water and dust blast. The depressed surface then rebound, bouncing cold icy dust over a fairly broad area of the surface of the comet airbourne.

So I guess, not so much a clang like a bell, but the vibration of a kettle drum.

But like everyone else, I did not predict dust, and the complete absence of Iron from the spectra doesn't help.

O'Hearn needs to release more data that supports his model...As is, I don't buy it.

__________________
jwj

It's ok not to know. We should try harder to find out.

The "snowy dirtball" theory specifically means there is more dirt than ice in the comet.


Bob Clark

Welcome back Jerry!!

I once almost got myself "banned" with my multiple-split-personalities (per my disclaimer below), so I understand how it feels to not be, certainly leaves me humbled. I also once thought I had comets figured out, as per this,
where I wrote: ...but I must admit I'm not sure anymore. If comets are solar system "scrubbers", gathering up dust way out there in the cold of outer system, and releasing dust in the warmer regions close to the Sun, it sort of makes sense to me. But this raises more questions than answers for me, since then comets are not primordial but rather current things. So I really don't know anymore. And the craters on Tempel1, how to explain those, if comet is not that dense? What about Halley's comet? Is it a "fluff ball" too?

Glad you're back!

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Maybe this is a simple question.... I read A'Hearn today say that the comet was maybe "75 to 80% empty space". Doesn't this mess with predicting the trajectory of the comet? I mean, how can the density be 1/5th of what it was originally believed to be? Does that mean it has a really dense core to bring it's total mass up to speed? Or am I just missing something?

Thanks!

I think there might be another reason that A'Hearn doesn't want to see any craters on comets; if they are impact craters, then the formation scenario would have trouble finding a dense enough environment for those impacts to happen. Plus, what would an impact do do a "fluffy no-ball" that is 75-80% empty space?

Maybe it has to do with how this is measured, I'm not sure if the trajectory of the flyby satellite was used, or if other measurements were used, I wouldn't want to guess anything without the data from the Rosetta lander, at least that would give better clues to what a comet is made of.

Cheers.

The mass of the comet is so small relative to that of the Sun and the planets that I doubt variations would make much of a difference - for most purposes, its mass is probably treated as zero, anyhow.

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Everything I need to know I learned through Googling.

This is what I could find on A'Hearn's density calculation of Tempel 1 (from the Planetary Society weblog)

This should be compared to the orbital and flyby calculations, does anyone know these values?

Cheers.

I agree that Rosetta will tell us a lot more. Future (yet-unplanned) missions will tell us yet more. I think it would be interesting to build another deep-impact type probe to target the next comet coming in with a hyperbolic trajectory (a few percent of all comets seem to come from outside the solar system). Of course next time we'll want a string of flyby cameras, not just the one, and a few more specialized instruments, such as a high speed high resolution camera that can get spectra from the initial flashes.

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Forming opinions as we speak

Gravity based soley upon ejecta trajectories ignores (or at best approximates) bouyancy - collision with both gas and fine particulate still propagating from, and in temporary kinetic and triboelectric suspension above the nucleus. It is difficult to explain a density of 0.6g/cc when most of the minerals excavated (or bounced off of the surface) have densities > 2g/cc. If the core is so hollow, why isn't the dust falling into the cracks???

If average particle size is 10microns as advertised, that SHOULD return a bulk density factor of greater than 90% of the solid volume, giving us a density of not less than 1.8g/cc, or 1.4g/cc if the internal nucleus is 50% water - which should also help fill the voids - remember, they found carbonates and other compounds that are only know to form at temperatures > 273K, so the ice making up whatever percentage of the comet was likely at one time, water. Structurally, IAOTO it would take a complex silicate or organic matrix to reduce the density to 0.6g/cc. Any sign of spider webs? There should be cracks, caves and fissures on the surface. There are none. Anyone ever find a geod full of ice and dust?

I don't think that the fly-by would have been close enough to measure a gravimetric perturbation, and the probe was knocked about enough that there would be no hope of recovering a reasonable estimate from the probes acceleration. Orbits are good for estimating the mass of the sun (where Mass sun>>>>Mass Comet and r~1AU), but worthless in estimating the mass of the comet. A reasonable density determination may have to wait for Rosetta. 0.6 g/cc fails too many sanity checks.

__________________
jwj

It's ok not to know. We should try harder to find out.

Does anyone have access to the on-line Science articles, the subscription I have does not allow me to see the on-line Deep Impact articles, the publications in Science journal will be "several weeks" later. Please PM me.
Thanks.

I read the editorial and the abstracts and it seems the message is that the DI mission found sort of what they expected with only one new surprise, the surface shows layering. Everything else is more or less "as expected", or "not too far from what planetary scientists foresaw".

I guess the one thing that distinguishes comets from other celestial objects, their jets and coma, is not worth talking about from the DI point of view. How do these jets form?

Cheers.

Did they find what they expected, or did they jam what they found into the what-we-expected box? Clays and Carbonates - not part of the standard model. Apparently this was not a big surpise to some, but I can't find any references stating comets would likely contain these types of molecules.

I also remember being taught that comets were not covered with dry dust liek the moon, because of their formation history, low gravity, high moisture content, and frequent 'sweeping' by the solar wind.

A layer of dry dust creates an obvious mechanism for jets: Static electric discharge. Dry silicates with an icy (conductive) interior or underskin: a Leydon jar, charged by continuous interaction with the solar wind. The jets might be localized, where either the dusty layer has been blown off, or is naturally more conductive or geometrically shaped for isolating charges with long lasting periodic capacitive discharges, heating the ice that is released as pressurized water vapor. If this is true, the IR of water vapor very near the comet surface should be quite warm.

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jwj

It's ok not to know. We should try harder to find out.

Deep Impact wasn't built to study such phenomena. And we've already sent several probes to study the coma. The jets are about the only major features left to investigate closely, and we seem to have a pretty good grasp on how they're formed. Perhaps a future probe will be designed to specifically study them.

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Avatar courtesy of Bunny.

Could you point to those papers where they show their "pretty good grasp"? I have the idea that especially the jets are poorly understood.

Cheers.

Well modeled? Well understood? As expected? From Wikapedia:

.

The obvious implication here is that the water contained in comets has never been unfrozen, therefore, there should not be any clays or carbonates. We should now suspect either: 1) Tempel 1 has a warmer past or 2) The outer solar system contains materials that had a warmer past or 3) Tempel 1 did not form in the outer solar system or 4) amaze your freinds with a new comet theory, because the old one is flawed.

DEAD Wrong! Deep Impact results indicate comets have very low thermal inertia; cooling very quickly: The fine dust on the surface is an excellent insulator, and most of the thermal energy is quickly radiated away.

Wrong again! Yes? No? Some organics have been spotted, but simple ones.

Well stated, and a sullen contrast with 'we saw what we expected'. The mission was launched because we were not sure what to expect.

There is nothing about Tempel 1 that suggests unknown physical processes, no anti matter, no exotic or unknown chemistry, nothing at odds with existing physical theory. But what is known about comets, or at least about this comet is very different from the most widely accepted theoretical expectations, especially with regard to the composition and formational history of the solar system. Stating otherwise demeans the importance of the knowledge gained from the Deep Impact probe.

There is still much to learn.

__________________
jwj

It's ok not to know. We should try harder to find out.