[X] My Assistant

[Guest_BruceMoomaw_*]

Let me add to that list my previous question:

(6) Could the very high temperatures in the immediate vicinity of the impact have synthesized the detected carbonates after all?

[The Messenger]

One -

The dust no one expected - is this an indicator that the density of the comet, and therefore the gravitational attraction, was possibly greater than expected? Is anyone trying to quantify how much of the dust resettled on the probe, and how much was blown away by the solar wind? This has implications for how the comet became dusty in the first place.

As an asside - Rosetta -http://www.williams.edu/Astronomy/jay/chapter19_etu6.html

Samples of material supplied by the Lander's Drilling and Distribution system (SD2) will be placed in a small oven and heated in stages up to 800C. Gases released from the ices will then be analysed to determine their composition.

67P is characterized as a 'dusty' comet.

A successful landing may lead to a GC choked with dust, not ices. Yes?

Edited to add: I checked with a chemist who works with GC's in adverse environments. At particle sizes ~2u it becomes difficult to both filter and control flow rate, as frits quickly plug.

[elakdawalla]

I am sitting in the press room at DPS, having just finished pounding the keyboard for my first blog entry from the meeting, and I am witnessing some very strange behavior on the part of Carey Lisse. He has just come into the room waving spectra and boasting about data he has and talking about giving his press conference talk early, on Tuesday, instead of Wednesday as scheduled, and talking about all his connections with various people on the Deep Impact team. But this is not typical behavior for a scientist; he's definitely grubbing for attention, which immediately makes me concerned about what message he's trying to sell me, and why he's working so hard to sell it. I started writing some stuff down and he saw me start to type and told me not to write down anything that he was saying. The BBC radio guy iwho is here is trying to tell him about responsible behavior for scientists and the Science embargo. It's all really odd.

Emily

[The Messenger]

Deep Impact is touching a lot of raw nerves, and no matter what model emerges, it will have to be sprinkled with dust. Data, please data.

HASI recorded an increase in the permittivity of the Titan surface at 12 minutes after impact.

What It would take some serious outgassing / chemical compositional change / fluid movement to modify the permittivity. Perhaps there really is a mooning Titanian, and he is a sand worm

They don't know what it means, and are working first to rule out anything that might be coming from within Huygens to cause that observation...But to do that, they need data from all the other science teams, and individual teams are often reluctant or at least slow to share the necessary data.

http://planetary.org/blog/20050905.html

This is disheartening. I can understand why some data is being withheld from the public (but I don't like it). For the teams trying to analyse and reduce such puzzling data to not share every piece of the puzzle with each other is retarded.

Stardust is scheduled to land in the Utah Desert in January of 2006. I propose we get together and fund a helicopter to intercept and pirate the probe to a secret laboratory that allows complete internet access to all the data as it emerges. Otherwise, the PIs will spirit it off like Genesis, and disappear forever.

[djellison]

For the teams trying to analyse and reduce such puzzling data to not share every piece of the puzzle with each other is retarded. 

I totally agree. It almost seems that one instrument is happier to share data with an instrument on a foreign spacecraft, before sharing it with it's neigbours onboard it's own spacecraft.

Doug

[The Messenger]

O'Hearn is reporting basically the same interpretive model as Lisse.

http://spaceflightnow.com/news/n0509/06deepimpact/

In a couple of seconds the fast, hot moving plume containing water vapor left the view of the spectrometer, and we are suddenly seeing the excavation of sub-surface ice and dust,

I am having all kinds of problems envisioning how a solid body could be filled with dusty ice, and how a probe could excavate subsurface ice after a violent heat exchange at the surface.

I see a timpanic model as more consistent with the observed shallow craters: A dust laden, but resilent surface that absorbed some of the energy, then the surface rebounded, flexing a circular shock wave across the surface, liberating ambient fine dust and ice from the adjacent surface terrain.

If this is correct, there should be secondary surface waves, and at least one harmonic in the explosion of dust, roughly consistent with the first interval.

[antoniseb]

I see a timpanic model as more consistent with the observed shallow craters: A dust laden, but resilent surface that absorbed some of the energy, then the surface rebounded, flexing a circular shock wave across the surface, liberating ambient fine dust and ice from the adjacent surface terrain.

Do I understand correctly that you are suggesting that the comet's surface is like a sand covered snare drum, and that the probe's collision stretched the surface, and it rebounded elastically? That can't be what you mean, but it's what I keep reading.

It could be that the top layers are fluffy, but ice free, and that after penetrating several meters of fluff the probe hit something more like the icy dirt that we've been saying comets are made of. I think that's what the paper is trying to say.

[The Messenger]

Do I understand correctly that you are suggesting that the comet's surface is like a sand covered snare drum, and that the probe's collision stretched the surface, and it rebounded elastically? That can't be what you mean, but it's what I keep reading.

Yes, that is what I mean, only a surface more like the earth, or a meteor. Yes, I will agree the interpretation that the probe 'punched through' is more consistent with models of what a comet should be, but I do not see how the interior of any solid object could be composed of very fine dust. Notice that the probe cannot be responsible for creating the dust, because this would have elevated the temperature and produced a more consistent IR spectra. And why would dust and or ice be ejected? A dust-filled nucleus would absorb energy like a Kevlar vest. If not, the compression necessary for a kinetic rebound should have melted the internal ice and ejecting a cloddy, muddy slurry, not dust and ice.

It could be that the top layers are fluffy, but ice free, and that after penetrating several meters of fluff the probe hit something more like the icy dirt that we've been saying comets are made of. I think that's what the paper is trying to say.

"Several meters' of dust would have a very high surface area. This would almost certainly absorb significant amounts of the underlying moisture...[thinking out-loud here] without which, this dusty layer would have a high dielectric strength and charge loading potiential. Moving against the solar wind, look at the potential for 'lightning strikes' within a comet! What a great primary mechanism that explains why comets are comets!

How deep the probe penetrated: It all boils down to the intensity of the initial UV spike. I am wondering if the CCD saturated and the energy released cannot be quantified - this would explain why they have not released an impact temperature. But even a saturated signal would provide a lower limit.

Edited to add:
According to Emily's Blog today, the spectra at the moment of impact was missed, A'Hearn stating that it would have saturated. She also states that the probe hit on a glancing blow - 20-36deg ...Now I'm confused, because there were images released on July 4th that definitely recorded the impact in the visual spectrum - how could the IR have been cockeyed?

http://planetary.org/blog/20050905.html

The science team is not convinced that we have seen the crater yet...A'Hearn quickly slid through several dozen attempts by the imaging team to process the images in ways that would reveal the crater, but I will verify that there was absolutely nothing in any of the images that looked convincingly like a crater (or even much of anything at all).

Two possibilities: 1) The dust hid the crater. 2) There is no significant crater, just a big cloud of surface dust.

Jessica Sunshine talked more about the post-impact spectra. They contained evidence of "literally glowing water, carbon dioxide, and organics in C-H bonds. The gases all had temperatures on the order of a couple of thousand Kelvin."

That is awful hot gases for a probe penetrating an object with 75% void volume, and no appreciable surface strength. Something is not right.

[SigurRosFan]

NASA's Spitzer and Deep Impact Build Recipe for Comet Soup

http://www.jpl.nasa.gov/news/news.cfm?release=2005-144

--- When Deep Impact smashed into comet Tempel 1 on July 4, 2005, it released the ingredients of our solar system's primordial "soup." Now, astronomers using data from NASA's Spitzer Space Telescope and Deep Impact have analyzed that soup and begun to come up with a recipe for what makes planets, comets and other bodies in our solar system. ---

[Guest_RGClark_*]

NASA's Spitzer and Deep Impact Build Recipe for Comet Soup

http://www.jpl.nasa.gov/news/news.cfm?release=2005-144

---  When Deep Impact smashed into comet Tempel 1 on July 4, 2005, it released the ingredients of our solar system's primordial "soup." Now, astronomers using data from NASA's Spitzer Space Telescope and Deep Impact have analyzed that soup and begun to come up with a recipe for what makes planets, comets and other bodies in our solar system. ---

Thanks for the link, Sigur. Here's another article on it:

Composition of a Comet Poses a Puzzle for Scientists
By KENNETH CHANG
Published: September 7, 2005
"In the burst of light after the collision, Spitzer detected specific colors of infrared light that indicated that Tempel 1 contained clays and carbonates, the minerals of limestone and seashells.
"Clays and carbonates both require liquid water to form.
"How do clays and carbonates form in frozen comets where there isn't liquid water?" said Carey M. Lisse, a research scientist at the Applied Physics Laboratory at Johns Hopkins University who is presenting the Spitzer data today at a meeting of the Division for Planetary Sciences in Cambridge, England. "Nobody expected this."
http://www.nytimes.com/2005/09/07/science/...html?oref=login
[may require free registration]

I'm surprised Lisse would say nobody expected the aqueous minerals to be seen. It is a well-known theory among comet researchers that radioactive heating may have allowed liquid water to form in comets early on in the Solar Systems history.
This theory was probably only controversial because it raises the possibility of life in comets, especially given the large abundance of organics, also confirmed by Deep Impact, in comets.


Bob Clark

[Stephen]

This theory was probably only controversial because it raises the possibility of life in comets, especially given the large abundance of organics, also confirmed by Deep Impact, in comets.

"Life" or merely some rather complex organic biochemistry? On the face of it, life as such surely still seems unlikely to evolve in a comet, if only because sources of energy in the interior it might use must surely be few and far between while those on the exterior would swiftly exterminate it.

======
Stephen

[edstrick]

Messenger: "That is awful hot gases for a probe penetrating an object with 75% void volume, and no appreciable surface strength. Something is not right. "


Uh... think of the awfully hot gasses for a meteorite penetrating an atmosphere.. with a density 0.00000something of the fluff on the comet's surface. You do bore in a bit, but by the time the impator/penetrator's punched through a dozen meters or so of "freeze-dried-icecream" or fluffy dust, it's pushed into the same mass per square meter as it's made of, has vaporized, and the vapor is mixed with the same amount of vaporized dust by mass, and is still is travelling downwards into the surface, but some gas is starting to expand / blowback out the hole. Hell yess it's gonna be hot!

[The Messenger]

Hell yess it's gonna be hot!

The problem is where the heat is: An extremely hot spectrum on impact, followed by an extremely cold one. To evacuated a deep cavitation, wouldn't the energy have to be carried by the probe - or the vaporized probe, to the "bottom", generating steam pressure that lifts the mass and causing the evacuation? The thermal energy should be distributed and not limited to the initial peak.

"In the burst of light after the collision, Spitzer detected specific colors of infrared light that indicated that Tempel 1 contained clays and carbonates, the minerals of limestone and seashells.
"Clays and carbonates both require liquid water to form.
"How do clays and carbonates form in frozen comets where there isn't liquid water?" said Carey M. Lisse

The spectrum tells us this comet is clearly not composed of virginal molecules: This comet has a terrestrial (warm) history. There is no reason, other than the rather iffy density determination, to assume this comet has a primal structure. Occur's razor preferentually places dust on the surface of a rock with obvious evidence of surface impacts. Since we can see no deep cavitation, and based upon the differential spectral temperatures, particle size, composition, impact angle, and icy state of the dust cloud, I see no reasonable evidence for A'Hearn's model. It is incredible.

[SigurRosFan]

New Spitzer Press Release: Tempel 1's Secret Ingredients Revealed

http://www.spitzer.caltech.edu/Media/relea...c2005-18a.shtml

--- Astronomers were most surprised to see clay, carbonates, and crystallized silicates because these chemicals are thought have formed in warm environments, possibly near the Sun, but away from the chilly outer neighborhood of comets. How did these compounds get inside comets? One possibility is that materials in our early solar system mixed together before being sorted out into individual bodies. ---

[Guest_BruceMoomaw_*]

The evidence is simply overwhelming, it seems, that "Messenger" is wrong, and that Tempel does indeed have a very low density with a surface layer of sun-dried dust covering an interior that still has a lot of water ice. Money quotes from various sources:

http://planetary.org/blog/20050905.html : "The surface temperature was 326 degrees Kelvin, 'nowhere cold enough to be at the sublimation temperature of ice. So the ice is not at the surface, it's below the surface.'

"The crater formed in a gravity-controlled regime, meaning that the impact happened into a material that had no significant strength holding it together. Which is pretty obvious from the dustiness of the ejecta. 'This wasn't a surprise' to most of the team 'but we're happy that we guessed right,' A'Hearn said. Almost all of the ejecta that came out of the crater was in the form of particles smaller than 10 microns, which is really tiny. The total ejected mass was about 10 or 20 million kilograms, and the plume remained connected to the surface for hours (which also would be expected from a gravity-controlled crater). The trajectories traced out by the ejecta allowed them to measure the force of gravity on the comet directly, and it came out to 50 milligal, or 50 parts in a million of Earth's gravity. That, in turn, lets you back out the mass of the comet, about 7 x 1013 kilograms. That, with the shape model, lets you calculate a density, 0.6 grams per cubic centimeter, but the density has large error bars, about plus or minus 0.35. But if you believe the 0.6 g/cc number, A'Hearn said, 'the porosity of Tempel 1 must be at least 75%. The comet's empty.'

"The size of the dust particles were 'mostly less than 10 microns, a mix of rocky dust and volatile solids.' They have lovely spectra from both before and after impact. A'Hearn showed a graphic illustrating that the slit of their spectrometer actually mis-pointed off of the impact site (down-range, off the southern edge of the comet), but that was 'good news' because otherwise the spectrometer would have saturated. There is a lot of information in the spectra. Water, carbon dioxide, and the C-H bond of organic molecules are obvious. Less obvious and more tentative identifications include methyl cyanide, sulfur dioxide, acetylene. 'The methyl cyanide is going to be controversial, because it looks like there is a lot of it.'

"Jim Richardson talked a little bit about the paths that the ejecta took. 'Less than 10% of the ejecta escaped the comet.' The material that made up the ejecta is extremely weak, with strengths measured at around 100 millipascals. But given the weak gravity at Tempel 1, this weak stuff can still hold a scarp. 'You can make a 20 or 40 meter scarp on a comet, but you couldn't pile it up a millimeter high on Earth.'

"Jessica Sunshine talked more about the post-impact spectra. They contained evidence of 'literally glowing water, carbon dioxide, and organics in C-H bonds. The gases all had temperatures on the order of a couple of thousand Kelvin.' Comparing pre-impact to post-impact spectra, Jessica said, they saw a 10-fold increase in the amount of water and carbon dioxide visible; but a 20-fold increase in the amount of organics. So there was a dramatic change in the abundance of organics, which they can't explain yet but has to do with what they excavated from the comet's interior. It's not clear yet whether it means that the surface is somehow depleted in organics, or maybe the organics at the surface are tied up in large grains so they only became visible when the impact dissociated all the large grains into little sub-grains.

"Jessica also said that they have discovered relatively recently that 'almost immediately after the vapor plume passes, we identified water ice. We have very strong evidence that we have water ice near the surface.' Remember, water ice can't be at the surface because the surface is too hot for it. Evidence suggests that the thermal inertia of the comet is nearly zero, meaning that it heats and cools quickly in response to sunlight, but the heating and cooling doesn't propagate into the interior...

"Pete Schultz reported that the observations of the impact flash, the continuous ejecta, the low velocity central plume, and several other details indicated that the comet was very porous, like the impact experiments he'd done into perlite. From the impact ejecta volume, he calculated a crater size of around 150 to 200 meters. But, he cautioned, the same volume could give you a 100-meter crater that was deep. And that the volume (and thus the crater size) could be greater for a very low surface density. He thinks that evidence suggests--but does not prove--that there is a highly porous surface layer, which is underlain by a weakly bonded upper 30 meters of the comet.

"Finally, Carey Lisse reported on the Spitzer observations. They have beautiful pre-impact and post-impact spectra. The post-impact one is full of features, a direct result, he said, of the fineness of the dust that the impact produced. He said that the impact must have broken apart aggregates into their component tiny grains. The spectra contain 'huge silicate features, indicative of fine dust.' The models of the impact process indicate that the impact produced 'gentle excavation of cold ejecta' and that 'the vast majority of the material was disaggregated on impact.' Among the features, the silicate features from minerals like forsterite and enstatite 'swamp' the other features, 'so our first job will be to understand' the abundances of the silicates. They saw 'a little hint of water in the first spectrum after impact but not much afterwards.' In addition to the enstatite, forsterite, and PAHs, they are trying to model their spectra using a library containing dolomite (a carbonate), smectite (a clay), spinel/hibonite, pyrrhotite, iron oxide, and elemental carbon grains. Lisse remarked that 'PAHs have never been seen before in a comet, but we expected them.' At which point ESA scientist Bernard Foing, who was sitting behind me, muttered 'no, they were' detected before. Lisse pointed out that he didn't yet have a suggestion for where all the iron and sulfur you would expect to see could be found.

"The carbonate and smectite that Lisse sees are the most controversial. As far as scientists understand it, it takes an aqueous (liquid water) environment to make these minerals. Yet the textural evidence suggests that Tempel 1 formed in the outer solar system. A'Hearn remarked that 'The high porosity tells me that things came together at very low speeds, far from the Sun, where the Keplerian velocities are very low, and with circular orbits, because elliptical orbits lead to high-speed encounters' and less porosity and more chemical alteration of the components of the comet. It would be difficult to form carbonate and smectite in the inner solar system and migrate it out to the outer solar system and not have a more violent birth for comets. So Lisse is going to have to work hard to prove that the carbonates are there. A'Hearn said 'it's premature to try to take our data, which we've only looked at 10% of in any detail, and apply it to the rest of the solar system at this point.'

"Someone asked Mike A'Hearn, 'with Deep Impact, did we learn about comets in general, or just Tempel 1?' A'Hearn's answer was that 'nothing may be typical' of comets. But if the high porosity result is true, then 'it's really hard to understand how you are going to attach the Rosetta lander to the surface' of its comet. 'They really have to think about that seriously. How well that's going to work with this incredibly weak stuff, I'm doubtful. Uwe Keller said yesterday he thought it would sink in. But I don't think its gravity is strong enough for it to sink in.' "

http://www.spaceflightnow.com/news/n0509/06deepimpact/ : "Mission data indicates the nucleus of Tempel 1 is extremely porous. Its porosity allows the surface of the nucleus to heat up and cool down almost instantly in response to sunlight. This suggests heat is not easily conducted to the interior and the ice and other material deep inside the nucleus may be pristine and unchanged from the early days of the solar system, just as many scientists had suggested.

" 'The infrared spectrometer gave us the first temperature map of a comet, allowing us to measure the surface's thermal inertia, or ability to conduct heat to the interior,' said Olivier Groussin, the University of Maryland research scientist who generated the map.

"It is this diligent and time consuming analysis of spectral data that is providing much of the 'color' with which Deep Impact scientists are painting the first ever detailed picture of a comet. For example, researchers recently saw emission bands for water vaporized by the heat of the impact, followed a few seconds later by absorption bands from ice particles ejected from below the surface and not melted or vaporized.

" 'In a couple of seconds the fast, hot moving plume containing water vapor left the view of the spectrometer, and we are suddenly seeing the excavation of sub-surface ice and dust,' said Deep Impact co-investigator Jessica Sunshine, with Science Applications International Corporation, Chantilly, Va. 'It is the most dramatic spectral change I've ever seen.' "


http://skyandtelescope.com/news/article_1589_1.asp : "The mass of Tempel 1's nucleus is around 72 trillion kilograms. The density is about 0.6 gram per cubic centimeter. That density, along with the gravity-dominated nature of the nucleus, has led team members to conclude that Tempel 1 is a porous rubble pile. This very loose body must be very weakly held together by gravity...

"The comet's outer layer is dusty fine powder. No blocks or boulders were seen flying from the impact site; only talcum-powder-like debris was observed.

"The spectrometer watched the ejecta plume expand outward. The observations revealed a distinctly layered comet. After the first blast of hot gas and plasma shot past the flyby craft's spectrometer, the instrument recorded a large peak due to water ice. 'It's the first thing we see after the hot vapor goes past. It must be near the surface,' says team member Jessica M. Sunshine (Science Applications International Corporation). The water was soon followed by a strong signal of organic materials...

"Team members conclude that far too much dust was released for it to have ever been heated by more than a few degrees. That suggests the material excavated by the impact is primordial — representing the original raw materials present when the comet first formed at the beginning of the solar system. 'Comets are the dinosaur bones of planet formation,' says Lisse. [This seems to put the last nail in the coffin of my theory that the possible carbonates might have been formed by the heat of the impact itself -- Moomaw.]

"The observed molecules are giving some experts pause, however. The spectra also show hints that Tempel 1 contains unexpected compounds such as carbonates and clays. By conventional thinking, these materials only form by chemical processing in the presence of liquid water. Thus, it's possible that the comet's ejecta might not have been 'primordial' after all. It might have been processed over billions of years. Can carbonates form inside a comet over extremely long time periods without liquid water? Did the comet melt enough for water to form? Future studies may provide answers."

Finally, regarding possible mechanisms by which carbonates might form in the very early Solar System, see one paper from the 2005 LPSC which claims to have found a mechanism by which carbonates can form in pre-planetary nebulas even without the presence of liquid water, through purely gas-phase reactions (
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1894.pdf ) -- which seems to
match well with the apparent detection of carbonates in such nebulas. I still think that the apparent absence of carbonates on the surfaces of comet nuclei, as opposed to their interiors -- and their scarcity (though not total nonexistence) in interplanetary dust particles collected out of Earth's upper atmosphere -- may be due to the fact that they're broken down pretty quickly by solar UV.