Spectrometer of James Webb Space Telescope

[Julian_M]

Can the James Webb Space Telescope 5–28 µm spectra spectrometer detect all substances and gases? If not, what specific substances can it detect? In the following James Webb chemical inventory analysis of comet 3i/Atlas:

https://arxiv.org/pdf/2601.22034

They detected Co2, Co, Methane, Nickel in the comet. But it didn't mention about Methanol which was detected last year (see below). Does it mean there is still Methanol being produced that the James Webb can't detect or does it mean no more Methanol now? If JWST can't detect Methanol. Why is that? The methanol detection paper is here.

https://www.arxiv.org/pdf/2511.20845

In general. How do you know what substances can be detected by 5–28 µm spectra? Why can't 5–28 µm spectra detect Methanol? What substances or gases by be detected by 5–28 µm spectra? And how exactly?

 

[renormalize]

Why can't 5–28 µm spectra detect Methanol?

Your second citation reports detecting methanol ($\text{CH}_{3}\text{OH}$) in the coma of comet 3I/Atlas via spectral measurements at wavelengths around $900\,\mu\text{m}$, using the Atacama Compact Array radio telescope. In contrast, the JWST IR spectrometer employed in the first reference operates at much shorter wavelengths ($5-28\,\mu\text{m}$). Unfortunately, in this range the fluorescence spectrum of methanol is weak and easily obscured by that of other compounds like water, which is likely why no detection of methanol is reported in that reference.
Instead, optical astronomers turn to even shorter wavelengths around $3\,\mu\text{m}$ to measure the spectrum of organic compounds like methanol in comets. You might read, for example, this paper containing NASA Infrared Telescope Facility data for comet Leonard in 2022: Strongly Depleted Methanol and Hypervolatiles in Comet C/2021 A1 (Leonard): Signatures of Interstellar Chemistry?
In particular, examine this spectrum for $\text{CH}_{3}\text{OH}$:

and note that the wavenumbers shown correspond to a wavelength range of about $3.3-3.4\,\mu\text{m}$.
Bottom line: no particular significance can or should be attached to the lack of methanol in the JWST assay of 3I/Atlas's composition.

 

[Julian_M]

Thanks. About Methane in the first paper. Can you mention other comets where release of chemicals was regulated.

Pre-perihelion Webb observations from August 2025 (as reported here) found that 3I/ATLAS is unusually rich in carbon-dioxide (CO2) relative to water (H2O) carrying 87% versus 4% of the total mass loss rate in gas phase, respectively, with most of the remaining 9% being carbon monoxide (CO). The new post-perihelion data implies a CO2/H2O ratio that is half that much or similar for the two epochs of JWST/MIRI spectroscopy, respectively.

The most notable finding from the new data is the robust detection of methane (CH4) production. The production rates of methane molecules in the two observing epochs are 13.7% and 27% of the water molecular production rate, respectively.

The delayed onset of CH4 production raises interesting questions regarding the history of 3I/ATLAS. Solid-phase methane is hyper-volatile, with a significantly lower sublimation temperature than carbon dioxide (CO2). This implies that methane ice near the surface of 3I/ATLAS would have been vigorously sublimating at the time of the first reports of outgassing from 3I/ATLAS before perihelion. However, neither the Webb observations nor the SPHEREx spectrophotometry from August 2025, detected methane. This suggests that methane is depleted in the outermost layers of 3I/ATLAS and was exposed to warming by sunlight only close to the Sun. Within this scenario, the early detection of carbon-monoxide (CO) outgassing on 3I/ATLAS presents an apparent quandary as CO is more volatile than CH4 and should therefore be depleted from the surface, yet it was detected prior to CH4.

 

[renormalize]

Can you mention other comets where release of chemicals was regulated.

Alas no, my familiarity with the literature of comets is too meager to offer suggestions.

This suggests that methane is depleted in the outermost layers of 3I/ATLAS and was exposed to warming by sunlight only close to the Sun.

Yes, exactly as is explained in the last paragraph appearing on pg. 9 of your first reference (https://arxiv.org/pdf/2601.22034) in post #1.

...the early detection of carbon-monoxide (CO) outgassing on 3I/ATLAS presents an apparent quandary as CO is more volatile than CH4 and should therefore be depleted from the surface, yet it was detected prior to CH4.

And that's also explained on pg. 10 of the same reference in the last paragraph.
What exactly is your point? You seem to just be regurgitating from that reference, likely using AI-generated text, rather than asking a real question.

 

[Julian_M]

Alas no, my familiarity with the literature of comets is too meager to offer suggestions.

Yes, exactly as is explained in the last paragraph appearing on pg. 9 of your first reference (https://arxiv.org/pdf/2601.22034) in post #1.

And that's also explained on pg. 10 of the same reference in the last paragraph.
What exactly is your point? You seem to just be regurgitating from that reference, likely using AI-generated text, rather than asking a real question.

I mean the methane part. If the outer most layer of methane was depleted in previous heating in another solar system, and no methane in one layer (this was why no methane detected last August 6 but only CO2). And now methane again (December). So the methane was kept in compartments or layers. I just want examples of other comets where the chemicals are in compartments or layers.

 

[renormalize]

I just want examples of other comets where the chemicals are in compartments or layers.

You can easily find these by searching for papers that compare pre- and post-perihelion comet activity. Here's one example that appears near the top of a web search:
Evolution of H2O, CO, and CO2 production in Comet C/2009 P1 Garradd during the 2011–2012 apparition
From the abstract:
...The observations of atomic oxygen serve as a proxy for H2O and CO2. We confirm the high CO abundance in comet Garradd and the asymmetry in the CO/H2O ratio with respect to perihelion reported by previous studies. From the oxygen observations, we infer that the CO2/H2O ratio decreased as the comet moved towards the Sun, which is expected based on current sublimation models. We also infer that the CO2/H2O ratio was higher pre-perihelion than postperihelion. We observe evidence for the icy grain source of H2O reported by several studies pre-perihelion, and argue that this source is significantly less abundant post-perihelion. Since H2O, CO2, and CO are the primary ices in comets, they drive the activity. We use our measurements of these important volatiles in an attempt to explain the evolution of Garradd’s activity over the apparition.
You should be able to find many more such analyses of comet behavior.

 

[Baluncore]

Should you also consider that the more intense sunlight may ionise CO₂ into CO and O ? Is that the source of the CO ?

 

[Julian_M]

The separate concern is the methane. How can methane hide inside the ice and not get released last August 6. It is only released last December. So I want example of another comet where the methane hides inside and get release much later. Or if this is the first for any comet. Usually all chemicals got mixed together in comets. Not some hidden inside compartments or layers to be released at specific time or schedule.

 

[renormalize]

...if this is the first for any comet. Usually all chemicals got mixed together in comets. Not some hidden inside compartments or layers to be released at specific time or schedule.

Did you not do me the courtesy of reading the article I posted?
I quote from pgs. 32-34:
"It is less clear what caused the reduction in the CO2 release to begin with.
One possibility is depletion of CO2 in the outgassing layers, but it seems that CO would also be depleted by this same mechanism, contrary to the much higher CO production rates observed post-perihelion. Another possibility is large scale compositional heterogeneity in Garradd’s nucleus. An active area rich in CO2 was preferentially exposed to sunlight pre perihelion and controlled the sublimation behavior at that time. Post-perihelion, another region rich in CO was exposed and drove the activity at that time. ...
If Garradd does exhibit large-scale heterogeneity in the CO2 and CO content of its ices, this could imply that Garradd consists of two or more cometisimals that formed in disparate regions of the protosolar disk. One part of the nucleus might contain CO-rich cometisimals that formed out near the CO ice line, whereas other parts might consist of cometisimals that formed closer to the CO2 ice line and are comparitively rich in CO2 and less abundant in CO. This is consistent with the early Solar System being a turbulent place, with mixing of material from various regions of the protosolar disk contributing to the formation of planetary bodies."

This same logic can be applied to the observed methane emission from comet 3I/ATLAS by assuming that it was formed via the ancient, extrasolar merger of two cometisimals (what a cool word!), one rich in CH4 ice and the other lacking it. During its path around the sun, the enriched portion was shadowed while incoming but was exposed to the sun on the outgoing leg, thereby emitting methane only during that leg. In other words, the same naturalistic explanation underlies the observed emission behavior of both comets Garradd in 2011-2012 and ATLAS in 2025-2026, obviating any need to seek some "artificial" cause.

 

[Baluncore]

Solid-phase methane is hyper-volatile, with a significantly lower sublimation temperature than carbon dioxide (CO2). This implies that methane ice near the surface of 3I/ATLAS would have been vigorously sublimating at the time of the first reports of outgassing from 3I/ATLAS before perihelion.

What is meant by "solid-phase methane" or "methane ice" ?
If the methane is held in the form of a clathrate, then methane will be released with the release of the water.