ITN: CO2 Powers Hartley !

[CraigS]

Originally Posted by Jarvamundo

Also notice Ahearn touched on the resolution of the spectrometer, saying the resolution of their onboard is pretty poor... said "keck" is better???... so i don't see your desire of actual surface points arc-ing spectro's being possible with this test.

OK. So I've been doing a bit of reading on this front.
Here we go … Deep Impact Instruments (2MB).

Section 5.3.6. IR Spectrometer Alignment, Wavelength Map and Spectral Resolution, Figure 27 (Page 90/91):

Figure 27 shows the spectral resolution at 137 K, the nominal flight temperature. The minimum geometric resolution is 216, which meets the required minimum of 200. Measurements of the line width for spectral lines of Kr and Ar that are known to be singlets shows that line widths are 1–1.1 binned pixels wide. At worst case the spectral resolution is 196.

Spectral resolving power is a measure of the ability of an instrument to resolve features in the electromagnetic spectrum. It is usually defined by:
R=λ/Δλ
where Δλ is the smallest difference in wavelengths that can be distinguished, at a wavelength of λ.

For comparative purposes, the Hubble "Space Telescope Imaging Spectrograph" (STIS) can distinguish features 0.17 nm apart at a wavelength of 1000 nm, giving it a resolving power of about 5,900. An example of a high resolution spectrograph is the Cryogenic High-Resolution IR Echelle Spectrograph (CRIRES) installed at ESO's Very Large Telescope, which has a spectral resolution of up to 100,000.

The graph shows the measured test results of the Spectral Imaging Module (SIM), which has a design bandwidth for detection from 1.05 to 4.8 micrometres. At the top end of 4.8 microns, its resolving power is about 400 which is around the mid point of its resolving range.

So, clearly there are more accurate detectors around but this beastie was designed specifically to fit on a spacecraft AND specifically to examine the nucleuii of comets at close range.

Ahearn's statement is valid ... as is the accuracy of the onboard technology (ie: it is certainly fit-for-purpose to detect H2O, CO2 and organic chemicals in their native modes).

So my only question now is, what emission spectral lines, (of typical, expected ie: 'known' comet compounds), might one expect to find in this band if electrically induced emissions were occurring ?

And are they present ?

Cheers

[CraigS]

Ok. So now I've found another relevant, (to spectra discussions), paper published 14th Jun 2010:

Detection of parent H2O and CO2 molecules in the 2.5–5 μm spectrum of comet C/2007 N3 (Lulin) observed with AKARI (700kB).

Comet C/2007 N3 (Lulin) was observed with the Japanese infrared satellite AKARI in the near-infrared at a post-perihelion heliocentric distance of 1.7 AU. Observations were performed with the spectroscopic (2.5–5.0 μm) and imaging (2.4, 3.2, and 4.1 μm) modes on 2009 March 30 and 31 UT, respectively. AKARI images of the comet exhibit a sunward crescent-like shape coma and a dust tail extended toward the anti-solar direction. The 4.1 μm image (CO/CO2 and dust grains) shows a distribution different from the 2.4 and 3.2 μm images (H2O and dust grains). The observed spectrum shows distinct bands at 2.66 and 4.26 μm, attributed to H2O and CO2, respectively. This is the fifth comet in which CO2 has been directly detected in the near-infrared spectrum. In addition, CO at 4.67 μm and a broad 3.2–3.6 μm emission band from C–H bearing molecules were detected in the AKARI spectrum. The relative abundance ratios CO2/H2O and CO/H2O derived from the molecular production rates are ∼ 4%–5% and < 2%, respectively. Comet Lulin belongs to the group that has relatively low abundances of CO and CO2 among the comets observed ever.

The spectrum is on page 14 and it is interesting to compare it with Hartley's (over, roughly the same, 2.5 to 5 micron band). Nowhere near as much CO2 as Hartley 2 .. a little more H2O though, and similar hydrocarbons (incl CO v(1–0) at 4.67 μm, organics at 3.2–3.6 μm) .. similar, but different to Hartley 2. They talk about a combination of CO, CO2, and dust thermal emissions at 4.5 μm, H2O 'emission' region of 2.7–2.8 μm.

I'm unclear as to whether they actually mean emission or absorption lines. (???).

The paper is an interesting read as it talks about up-to-date near-infrared and infrared detection limitations as well as about the spectra lines and their causes.

Cheers

[sjastro]

Originally Posted by CraigS

Ok. So now I've found another relevant, (to spectra discussions), paper published 14th Jun 2010:

Detection of parent H2O and CO2 molecules in the 2.5–5 μm spectrum of comet C/2007 N3 (Lulin) observed with AKARI (700kB).



The spectrum is on page 14 and it is interesting to compare it with Hartley's (over, roughly the same, 2.5 to 5 micron band). Nowhere near as much CO2 as Hartley 2 .. a little more H2O though, and similar hydrocarbons (incl CO v(1–0) at 4.67 μm, organics at 3.2–3.6 μm) .. similar, but different to Hartley 2. They talk about a combination of CO, CO2, and dust thermal emissions at 4.5 μm, H2O 'emission' region of 2.7–2.8 μm.

I'm unclear as to whether they actually mean emission or absorption lines. (???).

The paper is an interesting read as it talks about up-to-date near-infrared and infrared detection limitations as well as about the spectra lines and their causes.

Cheers

Craig,

IR is low energy. What you see are absorption lines. There is not enough energy to excite electrons into higher energy levels resulting in emission lines when the electrons return to the ground state.

As you decrease the wavelength of the radiation, the energy increases.
Visible and UV radiation will push electrons into higher energy levels. X-rays can remove electrons completely from a chemical bond resulting in ionization, gamma rays are the mother of all photons, apart from completely stripping an atom of it's electrons they can destroy the nucleus.

Regards

Steven

[CraigS]

Originally Posted by sjastro

Craig,

IR is low energy. What you see are absorption lines. There is not enough energy to excite electrons into higher energy levels resulting in emission lines when the electrons return to the ground state.

As you decrease the wavelength of the radiation, the energy increases.
Visible and UV radiation will push electrons into higher energy levels. X-rays can remove electrons completely from a chemical bond resulting in ionization, gamma rays are the mother of all photons, apart from completely stripping an atom of it's electrons they can destroy the nucleus.

Regards

Steven

Ok. Thanks.

These guys seem to be fairly loose in their use of the term 'emission lines' … (thanks for clarifying).

If I'm reading these papers correctly, it also seems that as a comet nucleus approaches the Sun, molecules can be excited to the extent that they can still exhibit lines in a fairly narrow band of the IR spectrum ?

Presumably, this is due to external (solar induced) UV excitation.

Cheers

[sjastro]

Originally Posted by CraigS

Ok. Thanks.

These guys seem to be fairly loose in their use of the term 'emission lines' … (thanks for clarifying).

If I'm reading these papers correctly, it also seems that as a comet nucleus approaches the Sun, molecules can be excited to the extent that they can still exhibit lines in a fairly narrow band of the IR spectrum ?

Presumably, this is due to external (solar induced) UV excitation.

Cheers

Craig,

This is a translated document and one of the better ones.

From experience many translated Japanese scientific and engineering documents end up in incomprehensible Jinglish.

Regards

Steven

[CraigS]

Err …. Ok .. I didn't realise that when I read it .. sorry about that.

The more interesting one is:

Previously unobserved water lines detected in the post-impact spectrum by R.J Baber et al University College London (Oct 2006).

In this one, they talk about 'Solar Pumped Flourescent' (SPF) transitions of H2O following the Tempel 1 impact. (SPFs are apparently transitions from doubly-excited stretch states).
The spectrum centred on the range 2.894 ±0.040 μm. They also talk about measuring secondary peaks shortly after impacts, which they attribute to Solar or Stochastic Heating (SH), (apparently states with 'three or four quanta of vibrational excitation'), although the actual mechanism that created these is still not fully understood, yet. (I think).

Interesting paper (and written in English).

Cheers

[Jarvamundo (Alex)]

Thanks for this info Craig. Cheers

[sjastro]

Craig,

I should have read the Japanese translated paper more carefully instead of assuming that translation errors occurred.

Their use of the term emission is quite correct.

When a molecule absorbs IR, the molecule is in an excited state. However when the molecule returns to the ground state thermal energy is released. Hence an absorption spectrum is observed.

For higher energy photons, the return to ground state emits photons hence an emission spectrum is observed.

Molecules also absorb thermal energy. In this case when the molecule returns to ground state IR is emitted.
The wavelength of the IR radiation emitted is a function of the amount of thermal energy absorbed.

So when CO2 and H2O are boiled off, thermal energy has been absorbed and IR is emitted.
The same principle applies to colliding objects into comets. Part of the impact energy is converted into thermal energy which excites the molecules and IR is emitted.

Hope this clarifies things.

Regards

Steven

[CraigS]

Hi Steven;

Many thanks for that explanation. I'm going way back into my dim, dark education here, but I do recall what you say .. must've actually learnt it somewhere !

Very interesting. A further question … when energy disturbs a body of gas in thermal equilibrium, would both emission and absorption spectra be observed to be occurring simultaneously ? (I'd guess the answer must be yes .. to varying luminosities .. and depending on the different states of the different parts of the gas body and the nature of the imposed energy).

To sustain any spectrum, clearly energy of some form would have to be added continuously at a fairly precise rate also. There must be other very particular constraints. Such as the pressure and density of the gas, the intensity of energy, the time variations over which the energy is applied, the regularity of the energy additions (if continuous), etc.

The presence and nature of such imposed energy must be precisely shown by the spectral lines, which in the case of the Tempel 1 impact event, clearly varies over time (30, 40 minutes to hours, days). If it doesn't vary, then the process causing the spectra would be continuous (or smoothly varying), over that same timeframe and the conditions of the gas must not vary, either.

Very interesting.

Cheers & Thanks.

[sjastro]

Very interesting. A further question … when energy disturbs a body of gas in thermal equilibrium, would both emission and absorption spectra be observed to be occurring simultaneously ? (I'd guess the answer must be yes .. to varying luminosities .. and depending on the different states of the different parts of the gas body and the nature of the imposed energy).

The answer is no.
Quantum mechanics states that the time for an energy transistion to occur such as an electron moving back to it's ground state is related to the energy difference between the excited and ground state. The larger the difference the faster the time for the transistions to occur.
Since a gas can undergoe various transistions at different energy levels none of the transistions occur simultaneously.

A spectrum is simply a record or snapshot of these transistions over a particular exposure time.

The presence and nature of such imposed energy must be precisely shown by the spectral lines, which in the case of the Tempel 1 impact event, clearly varies over time (30, 40 minutes to hours, days). If it doesn't vary, then the process causing the spectra would be continuous (or smoothly varying), over that same timeframe and the conditions of the gas must not vary, either.

The intensity of the peaks in either an IR absorption spectrum or IR emission spectrum relates to the concentration of the functional group causing the peak. Unfortunately this is not an absolute value.
By taking two IR spectra at different time intervals, any variations in the peaks allows one to calculate the emission rate of material from a comet.

As seen in the Japanese paper this is not a straightforward process.

Regards

Steven

[CraigS]

Originally Posted by sjastro

The answer is no.
Quantum mechanics states that the time for an energy transistion to occur such as an electron moving back to it's ground state is related to the energy difference between the excited and ground state. The larger the difference the faster the time for the transistions to occur.
Since a gas can undergoe various transistions at different energy levels none of the transistions occur simultaneously.

A spectrum is simply a record or snapshot of these transistions over a particular exposure time.

Ok. Got it - that's at the atomic scale of things. I think I was thinking of a 'cloud of gas' scale - one part of the cloud could be in the emission state another part of the same cloud could be in the absorption state ? (ie: different temperatures in the cloud).

Originally Posted by sjastro

The intensity of the peaks in either an IR absorption spectrum or IR emission spectrum relates to the concentration of the functional group causing the peak. Unfortunately this is not an absolute value.
By taking two IR spectra at different time intervals, any variations in the peaks allows one to calculate the emission rate of material from a comet.

As seen in the Japanese paper this is not a straightforward process.

Yep. I noticed that they calculate the amount of gas, (in molecules), by integrating the area under the peaks, over the timeframe during which they occur. This seems to be the answer to Alex's question of how they calculate the volume of gases instantaneously expelled .. and by doing this at different times, they can take the differences and work out how long it'll take for the nucleus to sublimate completely.

Also, for emissions: if the external energy (doing the excitation) has regular (or irregular) fluctuations (in terms of frequency), would the discharge emission frequencies also fluctuate ? Ie: higher frequency lines would appear and disappear ? -This being due to the amount of energy being delivered, being proportional to frequency of the excitation ? (Ie: the power/frequency distribution function).

Cheers

[sjastro]

Originally Posted by CraigS

Ok. Got it - that's at the atomic scale of things. I think I was thinking of a 'cloud of gas' scale - one part of the cloud could be in the emission state another part of the same cloud could be in the absorption state ? (ie: different temperatures in the cloud).

In this particular case no. You have a thermodynamic change of state with CO2/CO and H2O solids being converted into CO2/CO and H2O gases.
The solids will produce an absorption spectrum and the gases an emission spectrum since thermal energy has been absorbed by the solids to produce the gasses. IR is therefore emitted by the gasses.

Also, for emissions: if the external energy (doing the excitation) has regular (or irregular) fluctuations (in terms of frequency), would the discharge emission frequencies also fluctuate ? Ie: higher frequency lines would appear and disappear ? -This being due to the amount of energy being delivered, being proportional to frequency of the excitation ? (Ie: the power/frequency distribution function).

Consider the energy of the exciting radiation. It is defined as E=hv. h is Plancks constant, v is the frequency of the radiation.

An atom is composed of increasing energy levels that may or may not be occupied by electrons. For absorption of radiation by the atom to occur there needs to be a difference between 2 energy levels that equals the energy of the exciting radiation. Electron(s) are pushed into the higher energy level and photons are emitted when the electron(s) drop back into the lower energy level.
If you change the frequency of the exciting radiation, E changes and absorption no longer occurs.

Regards

Steven

[CraigS]

Steven;

Sorry for my persistence here and thanks so much from your answers. I really do appreciate them. They are certainly keeping me on track & I'm doing lotsa reading at the same time, also.

So what of flourescence ? (Eg: as in Tempel 1's 'Solar pumped flourescence'). I understand that flourescence happens when a substance absorbs light (or EMR) of a different frequency to that which the substance emits (which ends up being a lower frequency).

The reverse can also happen … the emitted light can end up being of a greater frequency, than what it absorbs.

So, in this case, if you didn't know the frequency of the exciting energy source, you could still work backwards from say, a particular higher frequency spectral line, to see what the frequency of the original exciting source was, and thus guess, as to where it might have come from.

I guess you could only do this if you know what the flourescing substance is to start with. I gather it would be possible to work out what the substance is, from the lower frequency absorption spectrum pattern (perhaps, in a different band), which should match with known substances ?

If the original exciting source was broad spectrum and high energy, there would be lots of flourescence, ie: emission lines corresponding to every element and compound in either crystalline (solid) or gaseous state in probably, all bands (?). If there's not a lot of flourescence lines, then the exciting energy can be assumed to be fairly low (?)

If the exciting source was broad spectrum, sporadic or irregular, and high energy, then the spectrum would change from measurement to measurement. If it were continuously broad spectrum and high energy the lines would be persistent from photo to photo (?)

Sorry about all my questions .. I don't expect a big answer … if I'm way off beam just tell me and I'll go away and read up more !

Cheers

PS: I notice phosphorescence is just a 'slow release' form of flourescence.

[Jarvamundo (Alex)]

Thanks Craig and SJ! great thread.

Originally Posted by CraigS

Yep. I noticed that they calculate the amount of gas, (in molecules), by integrating the area under the peaks, over the timeframe during which they occur. This seems to be the answer to Alex's question of how they calculate the volume of gases instantaneously expelled .. and by doing this at different times, they can take the differences and work out how long it'll take for the nucleus to sublimate completely.

Yeah, how to they *know* it is expelled?

To me this is a time varying measurement of existence. So i take it this tells us nothing of the function of how it came to be.

hmmm

[CraigS]

G'Day Alex;

(Gee I hope this thread has been of benefit to other folk also) !

Other than nucleosynthesis by a star, I don't know how else the gas could've appeared where it it is.

Can you elaborate on other possibilities ?
(gulp !)

Cheers

[Jarvamundo (Alex)]

The electric comet theory is the theory of the formation of these 'gases' from electrical processes.... that is combining with the sputtering of the surface material of the comet.... similar processes to those investigated by LCROSS

http://www.universetoday.com/76329/w...cross-results/

Then came the ‘much more.’ Between the LCROSS instruments, the Lunar Reconnaissance Orbiter’s observations – and in particular the LAMP instrument (Lyman Alpha Mapping Project) – the most abundant volatile in terms of total mass was carbon monoxide, then was water, the hydrogen sulfide. Then was carbon dioxide, sulfur dioxide, methane, formaldehyde, perhaps ethylene, ammonia, and even mercury and silver.

“So there’s a variety of different species, and what is interesting is that a number of those species are common to water,” Colaprete said. “So for example the ammonia and methane are at concentrations relative to the total water mass we saw, similar to what you would see in a comet.”

Colaprete said the fact that they see carbon monoxide as more abundant than water and that hydrogen sulfide exists as a significant fraction of the total water, suggests a considerable amount of processing within the crater itself.

“There is likely chemistry occurring on the grains in the dark crater,” he explained. “That is interesting because how do you get chemistry going on at 40 to 50 degrees Kelvin with no sunlight? What is the energy — is it cosmic rays, solar wind protons working their way in, is it other electrical potentials associated with the dark and light regions? We don’t know. So this is, again, a circumstance where we have some data that doesn’t make entirely a lot of sense, but it does match certain findings elsewhere, meaning it does look cometary in some extent, and does look like what we see in cold grain processes in interstellar space.”

The ideas and processes are not as far out as you may think.

[CraigS]

But there's no spectroscopic evidence of 'sputtering' !
(Which is the source of all that you say, which follows !)

Cheers

[Jarvamundo (Alex)]

Is there any on the moon? asteroids?

[CraigS]

Originally Posted by Jarvamundo

Is there any on the moon? asteroids?

I don't know.
The moon has jets though...

... and the astronauts weren't 'sputtered' during the moon landings !
… now there's an ugly image !

Cheers

[Jarvamundo (Alex)]

There is plenty of sputtering on all of these objects.

Your question is: Is there evidence of eletrical arc (or glow) discharge in a detectable range of the onboard equipment.

Sputtering happens with or without and answer of yes to the above question.

ie... happens on the moon, due to bombardment of solar wind. comets experience higher levels of this bombardment, sputtering is guaranteed to happen on the comet whether it be ice, rock or marshmallow.

If you can't see this simple fact, we have much to do!