ITN: CO2 Powers Hartley !

[Jarvamundo (Alex)]

Originally Posted by sjastro

Alex still has to address the hydroxyl radical in all of this.

I thought the radical was off the available charts? This does not exclude it from existence, i'd be interested if we do have a measurement on this tho?

Do you mean associated hydroxyl? The LCROSS electro-formation of H20 process has shown this is possible. I'm trying to find expectations of this process within an insulating plasma sheath.

Oh yea, Can i have a coherrent answer to my questions above too? fairs fair

[Outbackmanyep]

Originally Posted by Jarvamundo

Questions:
* What do you suggest the crust is made from? if no surface ice detected?
* Given the size of the explosion (blinded the camera to saturation levels), would the vaporization blow out this crust? It would have to yeah... if thats what you are claiming we see?

A couple of things, they did detect surface ice on 9P/ Tempel 1!
http://www.nasa.gov/mission_pages/de...water_ice.html
http://www.ncbi.nlm.nih.gov/pubmed/16456037


The sublimation of ices produces a porous dust mantle, this insulates the ices beneath the surface and perhaps regulates the rate of sublimation. The sublimation is believed to occur a few cm below the surface and the porous surface allows gases to permeate and escape. Heat flow through the surface provides the mechanism for this to happen. This is compatible with surface temps around 320K and for sublimating ices at 215K.
It has been observed that this process is not unform over the entire surface.
Infrared observations by Vega 1 and Deep Space 1 show that the surface temps of Halley and Borrelly were 312K and between 300 and 345K respectively.
Mind you water ice only really takes off for most comets at 3AU from the Sun, at further distances other ices begin to sublime, CO2 at 10AU, CH2O at 18AU etc.

[Jarvamundo (Alex)]

"A couple of things, they did detect surface ice on 9P/ Tempel 1!"

hmm it was 99.975% *not* surface ice on Tempel 1?
http://www.iceinspace.com.au/forum/s...76&postcount=5

So are we saying a "porous dust mantle" can support a spikey pinnacle hundreds of meters high? and kilometer sheer cliffs?

[sjastro]

Originally Posted by Jarvamundo

I thought the radical was off the available charts? This does not exclude it from existence, i'd be interested if we do have a measurement on this tho?

Do you mean associated hydroxyl? The LCROSS electro-formation of H20 process has shown this is possible. I'm trying to find expectations of this process within an insulating plasma sheath.

Oh yea, Can i have a coherrent answer to my questions above too? fairs fair

http://www.mps.mpg.de/en/aktuelles/p..._20101109.html

Regards

Steven

[Outbackmanyep]

Another thing i noticed on the images of 19P, 9P and 103P is that the smooth areas (which on 103P indicate an area of water ice sublimation) occur in the central regions of the nucleus.

[Outbackmanyep]

Originally Posted by Jarvamundo

"A couple of things, they did detect surface ice on 9P/ Tempel 1!"

hmm it was 99.975% *not* surface ice on Tempel 1?
http://www.iceinspace.com.au/forum/s...76&postcount=5

So are we saying a "porous dust mantle" can support a spikey pinnacle hundreds of meters high? and kilometer sheer cliffs?

Who ever said that a comet had 100% surface ice? Is that what you were expecting to find?
A porous dust mantle does not necessarily mean it is uniform over the entire surface or that it's uniform for all comets observed.
Do you see any spikey pinnacles on 103P, 19P and 9P?????
Anybody that has seen the images of 81P will see that it is different from the other 3 i mentioned.

[CraigS]

One of the things Ms Sunshine mentioned during the press conference was something about the dust collecting in the centre region. She (very briefly) alluded to gravity being involved. I think that might have a bit of a blooper!

The thing is too small to have any gravity. Perhaps the dust collects in the centre bit because that's where the axis of rotation is ?

Whaddya reckon ?

Cheers
PS: (Talking about Hartley 1 here).

[CraigS]

Hmm;

Announced this morning:
Stardust-NExT successfully fired its engines for the Tempel 1 revisit (on Nov 20). Intercept date is Feb 14, 2011:

Stardust-NExT will also measure the composition, size distribution and flux of dust emitted into the coma

Cheers

[CraigS]

Originally Posted by sjastro

Bremsstrahlung is a continuous spectrum. In the IR region (thermal Bremsstrahlung) it would be quite featureless compared to the IR spectrums showing H2O and CO2.

Alex still has to address the hydroxyl radical in all of this.

Regards

Steven

Hi Steven;

OK. I know this thread is a monster thread, but I've just gotta ask this question:

"Why is a Bremsstrahlung spectrum continuous, without peaks ?"

Cheers

[Outbackmanyep]

Originally Posted by CraigS

One of the things Ms Sunshine mentioned during the press conference was something about the dust collecting in the centre region. She (very briefly) alluded to gravity being involved. I think that might have a bit of a blooper!

The thing is too small to have any gravity. Perhaps the dust collects in the centre bit because that's where the axis of rotation is ?

Whaddya reckon ?

Cheers
PS: (Talking about Hartley 1 here).

If 103P didn't have any gravity it wouldn't exist i would think!
It may have a very insignificant amount but enough to keep most of it together!

Cheers!

[CraigS]

Originally Posted by Outbackmanyep

If 103P didn't have any gravity it wouldn't exist i would think!
It may have a very insignificant amount but enough to keep most of it together!

Cheers!

Ok .. point taken. Won't argue against the matter having some gravity.

I would think however, that the thing which keeps it together would be the chemistry of the 'glue' (whatever that substance might be) .. ie: mainly ionic bonds, etc.

The 'infalling' dust, following a CO2 jet outburst is what Sunshine was alluding to. Ie: why do particles of dust collect in the centre of the thing ?
There could be lots of answers for this and I would've thought 'gravity' would have fallen a fair way down the list. (In a turbulent, energetic atmosphere, of mixed particle sizes, there are lots of forces at play).

Anyway, just thought it was an interesting phenomenon to ponder .. I'm not pushing any one particular 'bent' about it all - its too complex for that



Cheers

[Jarvamundo (Alex)]

Originally Posted by CraigS

One of the things Ms Sunshine mentioned during the press conference was something about the dust collecting in the centre region. She (very briefly) alluded to gravity being involved. I think that might have a bit of a blooper!

The thing is too small to have any gravity. Perhaps the dust collects in the centre bit because that's where the axis of rotation is ?

Whaddya reckon ?

Cheers
PS: (Talking about Hartley 1 here).

Yeah i immediately thought that didnt make any sense

[Jarvamundo (Alex)]

Originally Posted by Outbackmanyep

If 103P didn't have any gravity it wouldn't exist i would think!
It may have a very insignificant amount but enough to keep most of it together!

Cheers!

unless it was a rock

[CraigS]

Originally Posted by Jarvamundo

unless it was a rock

Or a chunk of water/CO2 ice, or a big snowball with some melted ice bits, or some kind of hydrocarbon gunk, or any of the above !

Have you accounted for the low mass and density measurements, yet Alex ?

Lets get back on track, eh ?

Cheers

[Outbackmanyep]

Originally Posted by Jarvamundo

unless it was a rock

A single rock Alex? I don't think so

[Outbackmanyep]

The dust areas in the centre appear to be an area where water vapour is being ejected from the comet according to the EPOXI images, if the surface is dusty then it could mean that it's porous, if that's the case then there could be something going on under the surface. The CO2 is noticable as at the heliocentric distance the comet was at the time CO2 would have been highly volatile.

[sjastro]

Originally Posted by CraigS

Hi Steven;

OK. I know this thread is a monster thread, but I've just gotta ask this question:

"Why is a Bremsstrahlung spectrum continuous, without peaks ?"

Cheers

Craig,

Let's define what a peak (or line) is in an emission spectrum.

An emission spectrum is like a histogram defining the distribution of the number of emitted photons that fall on any particular wavelength. In a line emission spectra the photons fall into discrete frequencies which corresponds to the transistion of electrons over the energy levels.

In Bremsstrahlung, photons are emitted by the deacceleration of charged particles. The frequency of the photon is determined by the magnitude of deacceleration. The magnitude of deacceleration is random hence photons are emitted over a wide range of wavelengths.

As is no "preferred" wavelength the distribution of photons is essentially even. Hence the spectrum is continuous instead of discrete, and peaks and lines are not evident.

It is possible for absorption lines to be superimposed on a Bremsstrahlung spectrum if the charged particles absorb some of the Bremsstrahlung energy.

Regards

Steven

[CraigS]

Hmm ..

Very interesting .. might have a good think about that one … fascinating !

Thanks Steven.

Cheers

[CraigS]

The Latest EPOXI Findings on 103P/Hartley by Ahearn et al, have been published (16th June).

I thought I'd add the below info to this thread just for completeness .. (no mention of sputtering or electrical discharge, mind you .. ) …

Latest EPOXI findings on Comet Hartley 2 published

Main findings are:

…. confirmed that carbon dioxide is the volatile fuel for Hartley 2's spectacular ice-spewing jets.

The study also provides several new twists in the unfolding story of this small cometary dynamo including that: (1) the smooth, relatively inactive waist of the peanut shaped comet is likely re-deposited, and thus evolutionary rather than primordial material; (2) Hartley 2 has an 'excited state of rotation' because it spins around one axis, but also tumbles around a different axis; and (3) on its larger, rougher ends, the comet's surface is dotted with glittering, blocky objects that can reach approximately 165 feet (50 meters) high and 260 feet (80 meters) wide …. at this point we don't know whether these are deposits or growths, or something else …
...
"Hartley 2 is a hyperactive little comet, spewing out more water than other comets its size," .. "When warmed by the sun, dry ice [frozen carbon dioxide] deep in the comet's body turns to gas jetting off the comet and dragging water ice with it.

The latest reports (April 2011) are here:
The Carbon Monoxide Abundance in Comet 103P/Hartley during the EPOXI Flyby and ..
Rotation of Comet Hartley 2 from Structures in the Coma.

Cheers

[renormalised (Carl)]

Anything the EU say is a lost cause...all the results (including the latest) explain more than adequately what's going on.