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Posted by: JRehling Sep 14 2021, 05:44 PM

In the next year, if all goes well, JWST will have begun collecting data on the composition of terrestrial exoplanet atmospheres. This is potentially one of the most exciting developments in the history of science, but it's not going to be easy; here is a very informative preview:

https://arxiv.org/abs/2101.04139

Perhaps the key point is that, with the given signal to noise ratios, it may be possible to derive spectra with remarkable fidelity and spectral resolution, but the weak signal in most or all possible cases means that the number of required observations, to build up the signal, will be prohibitive given the limited lifespan of JWST and the large number of systems that we'll want to observe. Rather than campaigns that produce detailed spectra of many candidate "earthlike" planets, we will see the observation time divided amongst many exoplanets and spectra with moderate detail – but likely enough to determine presence or non presence of key molecules. This still depends, of course, upon the exoplanets themselves, whose atmospheres, surfaces, and clouds may make the signal weaker or stronger in any particular case, and those are variables which we cannot possibly control or predict.

To add some sad detail to this, the paper calculates that for some desired measurements, the number of transits that would have to be observed would be over 100 or even 1000, and this is flatly impossible. If the JWST were devoted to the observation of just one particularly special exoplanet and we wished to ignore all other uses of the telescope, this threshold would still be impossible, and obviously, there is no lack of priority targets for the telescope.

Among some molecules of highest interest, the ease of detection will be, in descending ease, CH4, CO2, H2O, O2, and for the planets in the TRAPPIST-1 system, the number of required observations to provide a useful signal for O2 will be on the order of 40.

It seems likely that what we'll see is campaigns to obtain some spectral data for about 15-25 (that is my sense, not a definitive total) candidate "earthlike" planets over JWST's first three or so years, and then more sustained campaigns to follow up on those planets that look most promising after the initial surveys. Overall, the use of JWST for this type of observation will require a very strategic budgeting of the resource of observation time, giving us a little data about a lot of the candidates, and – hopefully – much better data on the few most promising cases. The end result will depend on details that we can only guess at now.

No matter what turns up from JWST, there will always be the opportunity and need for future instruments to extend the studies outward and examine the candidates a little farther. If JWST's "horizon" for this sort of science is a radius of X parsecs, then a future instrument with 4 times the light gathering would extend it to 2X parsecs, and a volume in space 8 times greater. JWST will be the beginning of a great exploration outwards that will never conclude so long as we can keep building bigger and better instruments, decade by decade.

Posted by: Mongo Jan 2 2022, 11:01 PM

The JWST https://www.stsci.edu/jwst/science-execution/approved-programs/cycle-1-go include the following approved programs:

GO 1743 (12.7 hrs) -- Constraining the Atmosphere of the Terrestrial Exoplanet Gl486b
GO 1952 (15.5 hrs) -- Determining the Atmospheric Composition of the Super-Earth 55 Cancri e
GO 1981 (75.6 hrs) -- Tell Me How I’m Supposed To Breathe With No Air: Measuring the Prevalence and Diversity of M-Dwarf Planet Atmospheres
GO 2304 (17.9 hrs) -- Hot Take on a Cool World: Does Trappist-1c Have an Atmosphere?
GO 2420 (25.1 hrs) -- Probing the Terrestrial Planet TRAPPIST-1c for the Presence of an Atmosphere
GO 2512 (142.6 hrs) -- Seeing the Forest and the Trees: Unveiling Small Planet Atmospheres with a Population-Level Framework
GO 2589 (53.7 hrs) -- Atmospheric reconnaissance of the TRAPPIST-1 planets

Posted by: JRehling Jan 3 2022, 01:09 AM

This is tremendous. Many – perhaps most – of the Cycle 1 campaigns will revolutionize what we know about their respective subjects.

Some basic background information: Cycle 1 is one year, and TRAPPIST-1 can only be observed for ~100 days each year, around September 1. This means that those observations will be made almost as soon as possible once the nominal science mission begins. There is no proprietary period for one of the TRAPPIST-1 campaigns, so we seem to have a good chance of having basic atmospheric compositional data for several T1 planets by this time next year. To be succinct, there are no guarantees of any particular science return, even given nominal operations, due to all of the unknowns.

One other exoplanet campaign will be an observation of Alpha Centauri A looking for planets there.

Posted by: Mongo Jan 3 2022, 01:34 AM

Here are the specific observations of the red dwarf terrestrial planets targeted in the above JWST programs (a total of 50 transits):

55 Cancri e:
1 transit, NIRCam/F444W (CO 1952)
1 transit, MIRI/LRS (CO 1952)

GJ1132b:
2 transits, NIRSpec/G395 (CO 1981)

GJ341b:
3 transits, NIRCam/F444W (CO 1981)

GJ4102b:
3 transits, NIRSpec/G395 (CO 1981)

GL486b:
2 transits, MIRI/LRS (CO 1743)

TRAPPIST-1b:
2 transits, NIRISS/SOSS (CO 2590)

TRAPPIST-1c:
4 transits, NIRSpec/S1600A1 (CO 2420)
2 transits, NIRISS/SOSS (CO 2590)

TRAPPIST-1e:
2 transits, MIRI/F1500W (CO 2304)

TRAPPIST-1g:
2 transits, NIRSpec/BOTS (CO 2590)

TRAPPIST-1h:
3 transits, NIRSpec/PRISM (CO 1981)
2 transits, NIRSpec/BOTS (CO 2590)

WOLF 347b:
2 transits, NIRSpec/G395 (CO 1981)

TOI 134.01 (L168-9b):
3 transits, NIRSpec/BOTS (CO 2512)

TOI 175.01 (L98-59b):
2 transits, NIRSpec/BOTS (CO 2512)

TOI 260.01 (GJ1008b):
2 transits, NIRSpec/BOTS (CO 2512)

TOI 402.01 (HD15337b):
1 transit, NIRSpec/BOTS (CO 2512)

TOI 402.02 (HD15337c):
2 transits, NIRSpec/BOTS (CO 2512)

TOI 455.01 (GJ3193b):
1 transit, NIRSpec/BOTS (CO 2512)

TOI 562.01 (GL357b):
1 transit, NIRSpec/BOTS (CO 2512)

TOI 776.01 (LP961-53b):
2 transits, NIRSpec/BOTS (CO 2512)

TOI 776.02 (LP961-53c):
2 transits, NIRSpec/BOTS (CO 2512)

TOI 836.01 (HIP73427b):
1 transit, NIRSpec/BOTS (CO 2512)

TOI 836.02 (HIP73427c):
2 transits, NIRSpec/BOTS (CO 2512)

Posted by: Mongo Jan 3 2022, 01:51 AM

There is also the following:

GTO 1201 (193.6 hrs) -- NIRISS Exploration of the Atmospheric Diversity of Transiting Exoplanets (NEAT)

ABSTRACT
We will use NIRISS SOSS to acquire transit and eclipse observations of a sample of 14 exoplanets that span the full available range of equilibrium temperatures (300-3000 K) and masses (1 MEarth-10 MJup) for planets amenable to atmospheric characterization. Our observations will measure the abundance of the molecules and aerosols present in the exoplanets’ atmosphere and determine the vertical temperature structure of the hottest targets. These results will allow us to address fundamental issues such as the formation process and formation location of these close-in planets, the presence and characteristics of particulate clouds, and non-equilibrium chemistry effects that might be at play in their atmosphere. Six of our targets are rocky and for these we intend to place some of the first constraints on the mean molecular weight – and hence bulk composition – of their atmospheres. In particular, we will observe multiple transits of the potentially habitable earth-like planets TRAPPIST-1 d & f, aiming to make the first detection of the atmosphere of a habitable planet. Finally, for two targets, WASP-121b and LTT 9779b, we will acquire observations continuously throughout a full orbital period to constrain their temperature-pressure profile as a function of longitude and study how heat is absorbed and redistributed in their atmosphere.

TRAPPIST-1d:
5 transits, NIRISS/SOSS (GTO 1201)

TRAPPIST-1f:
2 transits, NIRSpec/BOTS (GTO 1201)

GJ357b:
1 transit, NIRISS/SOSS (GTO1201)

L98-59b:
1 transit, NIRSpec/SOSS (GTO 1201)

And the following:

GTO 1331 (22.5 hrs) -- Transit Spectroscopy of TRAPPIST-1e

TRAPPIST-1e:
4 transits, NIRSpec/BOTS (GTO 1331)

And the following:

GTO 1224 (49.2 hrs) -- Transiting exoplanet characterization with JWST/NIRSPEC

L98-59b:
1 transit, NIRSpec/BOTS (GTO 1224)

Posted by: Mongo Jan 3 2022, 02:04 AM

Combined transit list for the TRAPPIST-1 system:

TRAPPIST-1b:
5 transits, MIRI/F1500W (GTO 1177)
5 transits, MIRI/F1280W (GTO 1279)
2 transits, NIRISS/SOSS (CO 2590)

TRAPPIST-1c:
4 transits, NIRSpec/S1600A1 (CO 2420)
2 transits, NIRISS/SOSS (CO 2590)

TRAPPIST-1d:
5 transits, NIRISS/SOSS (GTO 1201)

TRAPPIST-1e:
4 transits, NIRSpec/BOTS (GTO 1331)
2 transits, MIRI/F1500W (CO 2304)

TRAPPIST-1f:
2 transits, NIRSpec/BOTS (GTO 1201)

TRAPPIST-1g:
2 transits, NIRSpec/BOTS (CO 2590)

TRAPPIST-1h:
3 transits, NIRSpec/PRISM (CO 1981)
2 transits, NIRSpec/BOTS (CO 2590)

Posted by: Decepticon Jan 3 2022, 08:49 AM

What!?

Proxima Centauri is not on those lists!

Posted by: Hungry4info Jan 3 2022, 11:17 AM

Proxima Cen b is not a transiting planet.

Posted by: JRehling Jan 3 2022, 12:56 PM

Reading between the lines (or in the proposals), there's a generally underlying strategy to the Cycle 1 exoplanet programs: These are efforts to make revolutionary observations, yes, but they're also exploratory, gauging the capabilities of JWST to make these sorts of observations, which is, one must emphasize, still very unknown until one makes the effort.

So many of these Cycle-1 programs are, naturally, aimed at making observations where a signal is more likely. The value of those will not only be to learn about one given world/system, but to establish how strong the signal is in those cases, and thereby judge which targets will be worthy of future observation time, and how much observation time will be needed.

The literature on JWST's ability to characterize terrestrial exoplanet atmospheres discusses situations where hundreds of transits might be needed to achieve certain detections. The Cycle-1 programs only involve about 2 to 5 transits per target. This is an exploration of the whole system – the stars, the planets, the atmospheres, and the JWST itself – and like the early questions in a game of Twenty Questions, will set up the more specific and perhaps time intensive campaigns to be made later.

I have no doubt that if JWST allocated a large fraction of its time to Proxima Centauri that it would collect data that scientists would love to have. But if that signal were weak or inconclusive, that might be a very poor return on the heavy investment. These Cycle-1 observations are going to make us much more knowledgable about which targets will be worthwhile for a lot (or, as the case may be, none) of the future Cycles' time.

Posted by: Mongo Jan 3 2022, 01:31 PM

More planned TRAPPIST-1 observations:

GTO 1177 (75.0 hrs) -- MIRI observations of transiting exoplanets

TRAPPIST-1b:
5 transits, MIRI/F1500W (GTO 1177)

The TRAPPIST-1 observations and spectroscopic observations of WASP-107b are being done in collaboration with the European MIRI GTO team (Wright PI).

GTO 1279 (26.3 hrs) -- Thermal emission from Trappist-1 b

TRAPPIST-1b:
5 transits, MIRI/F1280W (GTO 1279)

The program is conducted in coordination with a similar program from Tom Greene; the difference between the two programs being just the use of a different MIRI filter (15.0 microns versus 12.8 microns).

This program is considered as a first step towards future ambitious programs, requiring tens of eclipses to characterize spectroscopically the
atmosphere of Earth mass temperature exoplanets.

The earlier post listing approved transit observations of the TRAPPIST-1 system has been updated.

Posted by: Mongo Jan 3 2022, 01:46 PM

For context, the various programs listed above total almost a month of JWST time. Add in the many other exoplanet programs not listed above, and exoplanet observations constitute a very large fraction of the total planned observation time in the first year.

Posted by: JRehling Jan 4 2022, 03:39 PM

Thanks for these updates, Mongo.

A key point, similar to what I said in my last post here, from one of the program descriptions:

This Cycle-1 slate of programs is not at all aimed right at the bullseye of the planets and observations that we care most about: It's exploratory, looks at a lot of terrestrial-sized hot exoplanets that I'd never heard of and are not of intrinsically high interest, and doesn't in any case devote much very observation to any one planet. Instead, these programs focus on diversity of terrestrial exoplanets (range of temperatures and stars) and higher signal (larger and hotter ones). This will do a lot to calibrate the capabilities of JWST (and the nature of exoplanets atmospheres). The zero-proprietary period for many of these means that plans for future cycles can processed immediately… just getting out one landmark paper is not the point of all of this work.

I'm sure that in Cycles 3-6, etc., we're going to see a lot more targeting of the most interesting cases, and then there'll be a better idea of how much observation time is required for the desired goals or, in some cases, if the hopes cannot be achieved and a target will just have to be ignored to spend the valuable resource time on other cases.

For example, the most promising Kepler discovery, Kepler-452b, is deemed to have no chance of producing a useful signal, and will likely never be studied by JWST at all. It's not that the interest isn't there, but that the capability isn't.

There may be some blockbuster discoveries in Cycle 1, but what they're really doing is setting up success in future cycles, which is wonderful. The biggest discoveries might be coming in 2025 or so, but we won't know until we know!

Posted by: StargazeInWonder Jan 25 2022, 10:25 PM

This is a fascinating topic. I looked over the proposals and a list of known terrestrial exoplanets and came up with the perhaps-surprising, perhaps-sad count that there are only about two exoplanets known now that are (1) transiting, (2) less than 5 Earth masses, (3) receive a level of radiative heating between that of Venus and Mars, (4) are believed to permit a favorable signal to noise ratio for JWST to be able to characterize the atmospheric composition. Those are TRAPPIST-1 d and TRAPPIST-1 e.

It could always turn out that more candidate objects of interest will be confirmed before Cycle 3, etc., and could increase the list a little or a lot. There are a lot of unconfirmed TESS candidates now.

In addition, there are several nearby planets that fit this description but do not transit. It looks like Cycle 1 observations target few if any of those, but may be aimed at hotter terrestrial planets or larger cool planets which will establish how viable it is to characterize a planet's atmosphere without a transit. Those include Proxima b, Ross 128 b, Luyten's Star b, Teegarden's Star b, and Tau Ceti e. In principle, an almost transiting planet will allow us to subtract the light from the planet+star in one situation to the light from the star alone one half orbit later. The problem is, the star's output might vary over that span of time (for example, due to a sunspot), by much more than the signal from the planet.

So set your expectations appropriately. JWST might characterize only as few as two candidate "earthlike" planets. Or many more!

Posted by: StargazeInWonder Jun 3 2022, 05:15 AM

Another very important planet that will be observed by JWST is LHS 1140 b. It's the target of GO 2334:

https://www.stsci.edu/jwst/science-execution/program-information.html?id=2334

LHS 1140 b is rocky, very dense, receives about as much stellar radiation as Mars, and H2O has been detected in its atmosphere. Together with TRAPPIST-1 d and TRAPPIST-1 e, it's one of the most plausibly earthlike planets that JWST will observe. The big known difference from Earth is its high mass (6.5 ME). This is sure to be one of the most interesting observations in Cycle 1.

Posted by: Hungry4info Jun 3 2022, 09:22 AM

The HST H2O detection is not particularly secure. See the https://arxiv.org/abs/2011.08815v1:

Posted by: StargazeInWonder Jun 3 2022, 01:07 PM

That is important caution; I should have said that there's some evidence, but yes, not definitive. One of the exciting aspects of JWST observations, as opposed to HST, is that noise from the star will be much less in JWST's spectral range than in HST's. And that's one of the advantages that JWST will bring to, obviously, every exoplanet observation, not just this one.

Posted by: climber Jun 4 2022, 08:12 AM

New technique to detect oxygen in exoplanet atmosphere :
https://astrobiology.nasa.gov/news/new-technique-may-give-nasas-webb-telescope-a-way-to-quickly-identify-planets-with-oxygen/?utm_source=TWITTER&utm_medium=NASAAstrobio&utm_campaign=NASASocial&linkId=167838838

Question a bit out of topic : can somebody point me to book (s) for general public that sum up actuel knowledge about exoplanets ?

Posted by: Mongo Aug 25 2022, 10:00 PM

For those interested, here are the JWST observing schedules: https://www.stsci.edu/jwst/science-execution/observing-schedules

Updated weekly.

The exoplanet observations carried out or planned by Sep 5, 2022:

VISIT ID PCS MODE VISIT TYPE SCHEDULED START TIME DURATION SCIENCE INSTRUMENT AND MODE TARGET NAME
------------- ---------- ----------------------------- -------------------- ----------- -------------------------------------------------- ---------------
1366:4:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-10 T15:04:42Z 00/08:33:57 NIRSpec Bright Object Time Series WASP-39
1201:5:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-12 T01:34:35Z 00/05:02:16 NIRISS Single-Object Slitless Spectroscopy WASP-52
1201:4:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-12 T23:38:30Z 00/06:42:34 NIRISS Single-Object Slitless Spectroscopy HAT-P-1
1274:4:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-15 T00:38:14Z 00/08:34:31 NIRCam Grism Time Series HD-149026
2589:6:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-17 T04:41:12Z 00/05:17:05 NIRSpec Bright Object Time Series TRAPPIST-1
2589:1:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-18 T14:00:06Z 00/05:04:32 NIRISS Single-Object Slitless Spectroscopy TRAPPIST-1
2589:2:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-20 T02:15:42Z 00/05:04:32 NIRISS Single-Object Slitless Spectroscopy TRAPPIST-1
1803:1:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-20 T14:57:37Z 01/17:24:00 MIRI Low Resolution Spectroscopy GJ-1214
1366:2:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-22 T19:09:32Z 00/08:30:22 NIRCam Grism Time Series WASP-39
1366:1:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-26 T20:53:14Z 00/08:41:59 NIRISS Single-Object Slitless Spectroscopy WASP-39
1386:2:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-30 T00:55:56Z 00/01:45:04 NIRCam Coronagraphic Imaging HIP-65426
1386:3:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-30 T03:29:15Z 00/01:45:04 NIRCam Coronagraphic Imaging HIP-65426
1386:11:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-30 T07:02:39Z 00/03:50:21 NIRISS Aperture Masking Interferometry HIP-65426
1366:3:1 FINEGUIDE PRIME TARGETED FIXED 2022-07-30 T21:45:28Z 00/08:36:05 NIRSpec Bright Object Time Series WASP-39
1386:19:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-02 T02:45:56Z 00/00:40:42 MIRI Coronagraphic Imaging HD-141569A
1386:20:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-02 T03:40:47Z 00/00:40:42 MIRI Coronagraphic Imaging HD-141569A
1386:22:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-02 T06:55:20Z 00/00:40:28 MIRI Coronagraphic Imaging HD-141569A
1386:23:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-02 T07:49:57Z 00/00:40:28 MIRI Coronagraphic Imaging HD-141569A
1386:25:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-02 T11:18:28Z 00/01:20:26 MIRI Coronagraphic Imaging HD-141569A
1386:26:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-02 T12:53:04Z 00/01:20:26 MIRI Coronagraphic Imaging HD-141569A
1274:5:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-04 T03:48:33Z 00/08:34:37 NIRCam Grism Time Series HD-149026
1386:17:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-07 T23:22:53Z 00/02:43:15 NIRCam Coronagraphic Imaging HD-141569A
1386:18:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-08 T02:18:10Z 00/02:43:15 NIRCam Coronagraphic Imaging HD-141569A
1366:21:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-11 T04:54:46Z 00/07:05:30 NIRISS Single-Object Slitless Spectroscopy WASP-18
1958:2:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-15 T18:41:12Z 00/03:16:07 MIRI Medium Resolution Spectroscopy V-CT-CHA-B
1386:17:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-18 T06:49:38Z 00/02:43:15 NIRCam Coronagraphic Imaging HD-141569A
1386:18:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-18 T09:44:53Z 00/02:43:15 NIRCam Coronagraphic Imaging HD-141569A
1633:3:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-23 T02:34:52Z 00/06:22:28 MIRI Medium Resolution Spectroscopy HD-189733
1274:10:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-24 T21:47:50Z 00/06:48:04 NIRSpec Bright Object Time Series WASP-77A
1633:5:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-25 T07:54:59Z 00/06:15:53 NIRCam Grism Time Series HD-189733
1274:1:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-26 T10:43:53Z 00/05:54:35 NIRCam Grism Time Series HD-189733
2708:1:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-27 T17:00:46Z 00/06:23:53 MIRI Low Resolution Spectroscopy LTT-1445A
1633:4:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-29 T18:23:41Z 00/06:13:58 NIRCam Grism Time Series HD-189733
2021:2:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-30 T22:09:06Z 00/04:51:43 MIRI Low Resolution Spectroscopy HD-189733B
1633:1:1 FINEGUIDE PRIME TARGETED FIXED 2022-08-31 T23:34:16Z 00/06:22:28 MIRI Medium Resolution Spectroscopy HD-189733
2021:1:1 FINEGUIDE PRIME TARGETED FIXED 2022-09-04 T08:38:50Z 00/04:51:43 MIRI Low Resolution Spectroscopy HD-189733B

Posted by: Tom Tamlyn Aug 26 2022, 03:59 AM

A belated reply: The Planet Factory by Elizabeth Tasker (Bloomsbury 2019) is a marvelous book.

https://www.bloomsbury.com/us/planet-factory-9781472917744/

Tasker is a British planetary scientist who is a professor at the Japan Aerospace Exploration Agency. She also has an active social media presence.

https://about.me/elizabethtasker

Elizabeth Tasker @girlandkat on twitter.

Edited to add one of the many admiring reviews of Planet Factory, this one from Caleb Scharf, Director of Astrobiology, Columbia University:

Posted by: climber Aug 26 2022, 09:34 PM

Thanks so much Tom, I’ll certainly take your advice

Posted by: Mongo Nov 22 2022, 02:20 AM

https://arxiv.org/abs/2211.10487

Transmission spectroscopy of exoplanets has revealed signatures of water vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres. However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations' relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species−in particular the primary carbon-bearing molecules. Here we report a broad-wavelength 0.5-5.5 μm atmospheric transmission spectrum of WASP-39 b, a 1200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with JWST NIRSpec's PRISM mode as part of the JWST Transiting Exoplanet Community Early Release Science Team program. We robustly detect multiple chemical species at high significance, including Na (19σ), H2O (33σ), CO2 (28σ), and CO (7σ). The non-detection of CH4, combined with a strong CO2 feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4μm is best explained by SO2 (2.7σ), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST's sensitivity to a rich diversity of exoplanet compositions and chemical processes.

https://arxiv.org/abs/2211.10488

Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems. Access to an exoplanet's chemical inventory requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based and high-resolution ground-based facilities. Here we report the medium-resolution (R∼600) transmission spectrum of an exoplanet atmosphere between 3-5 μm covering multiple absorption features for the Saturn-mass exoplanet WASP-39b, obtained with JWST NIRSpec G395H. Our observations achieve 1.46x photon precision, providing an average transit depth uncertainty of 221 ppm per spectroscopic bin, and present minimal impacts from systematic effects. We detect significant absorption from CO2 (28.5σ) and H2O (21.5σ), and identify SO2 as the source of absorption at 4.1 μm (4.8σ). Best-fit atmospheric models range between 3 and 10x solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO2, underscore the importance of characterising the chemistry in exoplanet atmospheres, and showcase NIRSpec G395H as an excellent mode for time series observations over this critical wavelength range.

https://arxiv.org/abs/2211.10489

Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining the dominant chemical processes at work and, if in equilibrium, revealing planet formation histories. Transmission spectroscopy provides the necessary means by constraining the abundances of oxygen- and carbon-bearing species; however, this requires broad wavelength coverage, moderate spectral resolution, and high precision that, together, are not achievable with previous observatories. Now that JWST has commenced science operations, we are able to observe exoplanets at previously uncharted wavelengths and spectral resolutions. Here we report time-series observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength photometric light curves span 2.0 - 4.0 μm, exhibit minimal systematics, and reveal well-defined molecular absorption features in the planet's spectrum. Specifically, we detect gaseous H2O in the atmosphere and place an upper limit on the abundance of CH4. The otherwise prominent CO2 feature at 2.8 μm is largely masked by H2O. The best-fit chemical equilibrium models favour an atmospheric metallicity of 1-100× solar (i.e., an enrichment of elements heavier than helium relative to the Sun) and a sub-stellar carbon-to-oxygen (C/O) ratio. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation or disequilibrium processes in the upper atmosphere.

https://arxiv.org/abs/2211.10493

Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has been challenging given the precision and wavelength coverage of previous observatories. Here, we present the transmission spectrum of the Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS instrument on the JWST. This spectrum spans 0.6−2.8μm in wavelength and reveals multiple water absorption bands, the potassium resonance doublet, as well as signatures of clouds. The precision and broad wavelength coverage of NIRISS-SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favoring a heavy element enhancement ("metallicity") of ∼10−30× the solar value, a sub-solar carbon-to-oxygen (C/O) ratio, and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are best explained by wavelength-dependent, non-gray clouds with inhomogeneous coverage of the planet's terminator.

https://arxiv.org/abs/2211.10490

Photochemistry is a fundamental process of planetary atmospheres that is integral to habitability, atmospheric composition and stability, and aerosol formation. However, no unambiguous photochemical products have been detected in exoplanet atmospheres to date. Here we show that photochemically produced sulphur dioxide (SO2) is present in the atmosphere of the hot, giant exoplanet WASP-39b, as constrained by data from the JWST Transiting Exoplanet Early Release Science Program and informed by a suite of photochemical models. We find that SO2 is produced by successive oxidation of sulphur radicals freed when hydrogen sulphide (H2S) is destroyed. The SO2 distribution computed by the photochemical models robustly explains the 4.05 μm spectral feature seen in JWST transmission spectra [Rustamkulov et al.(submitted), Alderson et al.(submitted)] and leads to observable features at ultraviolet and thermal infrared wavelengths not available from the current observations. The sensitivity of the SO2 feature to the enrichment of heavy elements in the atmosphere ("metallicity") suggests that it can be used as a powerful tracer of atmospheric properties, with our results implying a metallicity of ∼10× solar for WASP-39b. Through providing improved constraints on bulk metallicity and sulphur abundance, the detection of SO2 opens a new avenue for the investigation of giant-planet formation. Our work demonstrates that sulphur photochemistry may be readily observable for exoplanets with super-solar metallicity and equilibrium temperatures ≳750 K. The confirmation of photochemistry through the agreement between theoretical predictions and observational data is pivotal for further atmospheric characterisation studies.

Posted by: Bill Harris Nov 22 2022, 03:26 AM

Thanks for these updates, Mongo.

Not so much as superbly spectacular to the "typical enthusiast" as the initial set of images was, Webb is now settling into providing solid data. This exoplanetary atmospheric data is one example. Or the NIRCAM views of the Tarantula Nebula are a joy to zoom in on and pick through. This instrumemt will be a joy for many years!

Posted by: Mongo Dec 3 2022, 03:15 PM

Had tried to upload this listing of Trappist-1 observations with JWST as an Excel file, but was not allowed. Here is a screenshot:

Posted by: StargazeInWonder Dec 15 2022, 01:06 AM

JWST gets first glimpse of 7-planet system with potentially habitable worlds:
https://www.nature.com/articles/d41586-022-04452-3

There's hardly any news here, but this serves to summarize what we knew, and the status of a sliver of the many TRAPPIST-1 observations that take place in Cycle 1.

Extended, hydrogen-rich atmospheres had already been tentatively ruled out by HST observations for some of the planets.

Perhaps the most substantive news in the article is in the indirect reference to timeframes in which we might expect preliminary analyses to be published. "Within the next year we’ll have a family portrait."

Posted by: StargazeInWonder Dec 28 2022, 06:55 AM

Looking at the transiting terrestrial exoplanets that are, and aren't, being targeted by JWST in Cycle 1 has led to a somewhat obvious dynamic that hadn't fully clicked for me before: The candidate "earthlike" planets that are being observed are those which orbit unusually small red dwarfs. For obvious reasons, the signal to noise ratio correlates with the apparent size of the planet's atmosphere divided by the apparent diameter of the star. As a result, Kepler 186 and TOI 700, which have radii of 0.52 and 0.42 times that of the Sun are not promising targets, whereas planets orbiting TRAPPIST-1, LP 890-9, and LHS 1140, with radii of 0.12 to 0.21 that of the Sun, are targets.

That is a rather unfortunately broad restriction, and highlights how transit observations are not going to be promising for many terrestrial exoplanets, and in particular, perhaps not for any that orbit sunlike stars. The situation is made worse for observing terrestrial planets orbiting sunlike stars with ground-based telescopes, as the transits occur infrequently, and are likely to occur in part or entirely during daylight hours at any given telescope site.

As some studies have suggested that planets in the "habitable zone" of small red dwarfs might systematically lose their atmospheres because of the harsh environment near the star, this entire mode of observation may be dead on arrival for observing any earthlike (or even venus-like or mars-like) atmospheres. Of course, we will find out soon for the three stars mentioned earlier if this means of study has any promise or not.

If the observation of transiting candidate "earthlike" planets does indeed turn out to be futile, the next promising kind of study would be direct imaging studies of the spectra of resolvable planets orbiting nearby sunlike stars, like Alpha Centauri, Tau Ceti, and Epsilon Eridani (should such planets exist). And then we'll be waiting for ELT and GMT to come online about 5-10 years from now.

Posted by: HSchirmer Dec 28 2022, 01:56 PM

First thought: interesting observation, IIRC it also is selective for exoplanets with VERY short orbital periods- selection to observe multiple transits during the primary mission.

Second thought (tangent) "Dwarves"
There's a great 'mostly true' tale about JRR Tolkien submitting "The Hobbit" to his publisher, and getting the manuscript back with lots of red-line changes by the young junior editor who had been assigned to Tolkien's book. Tolkien's use of 'Dwarves' and 'Elves' was redlined and noted as 'Dwarfs' and 'Elfs' "cf OED 1920" (editor shorthand for "compare with Oxford English Dictionary, 1920 edition")

JRR met with the young editor and quietly stated the plurals are 'Dwarves' not Dwarfs, and 'Elves' not Elfs.
The junior editor reached over, took out the 1920 Oxford English Dictionary and flipped to 'Dwarfs'; whereupon JRR took the dictionary, opened it to the first page, grabbed an ink pen, and started writing.
The junior editor was flabbergasted, "What are you DOING?"
JRR, "I'm autographing a copy of my dictionary for my new friend; you see I was the EDITOR of the 1920 Oxford English Dictionary. I made a mistake about Dwarfs and Elfs, it really should be Dwarves and Elves. Just don't tell anybody..."

Posted by: Hungry4info Dec 28 2022, 02:14 PM

The planet-star radius ratio is definitely important, as well as the brightness of the star (in J band), but also the temperature of the planetary atmosphere (since the atmosphere scale height is a function of temperature and surface gravity). These combine as inputs for a formula called the "Transmission Spectroscopy Metric," which gives a guess of the signal-to-noise ratio of the planet's atmosphere absorption features (for an assumed clear atmosphere). These "TSM" values have been the guiding metric deciding JWST transmission spectroscopy targets, at least for these early observations.

A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
https://arxiv.org/abs/1805.03671

The paper also presents a similar "ESM" metric for emission spectroscopy.

Posted by: StargazeInWonder Dec 28 2022, 10:42 PM

Among planets that are of approximately earthlike temperatures, these are in effect the same selection. A main sequence star with small radius is always a very cool red dwarf, and so its "habitable zone" is very close and the orbital period very short.

There are also observations being made of very hot planets, in which case the orbital period may be short even if the star is larger.

It is a bit of bad luck in the case of TRAPPIST-1 that the star may only be observed for a short portion of the year, in order to maintain the protocol of keeping the sunshield in position. During those times, TRAPPIST-1 is getting a lot of JWST's time, since it can't be observed the rest of the year.

Posted by: StargazeInWonder Jan 2 2023, 10:14 PM

The matter of transiting planets aside, there is one more way for JWST to characterize an exoplanet, and that is by resolving it directly. So far, with perhaps two exceptions in the Alpha Centauri system, the only exoplanets that have ever been imaged directly have been hot, young planets in extremely distant orbits, because only a planet distant from its star can be resolved by existing telescopes and of those only a hot planet provides illumination. There are approximately eight nearby star systems that permit JWST to image planets in the light of their own star, and of those, two have planned observations upcoming:

Program 1618 Alpha Centauri A Jul - Aug 2023
Program 2243 Epsilon Indi A Apr - May 2023

Alpha Centauri Ab is a candidate exoplanet that has perhaps been observed already by VLT, and JWST is likely to settle the question of whether that was a detection or something else. Epsilon Indi Ab is a confirmed planet, discovered by radial velocity, of about 3 MJ in a Saturn-like orbit which, at a distance of 11 AU, is likely to be near or at the top of all exoplanets in terms of apparent diameter: Only a Neptune-plus-sized planet in the Alpha Centauri system or a jovian planet orbiting one of the few stars within 12 light years could match it in that regard. The proposal for the observation of Epsilon Indi A expresses high confidence that the planet will be easily observable and that 4 observations will measure the planet's temperature, the first time this ever will be done for a planet that isn't [believed to be] glowing hot in visible wavelengths.

It seems like a fair bet that in Cycles 2 and 3, there will be direct observations of other nearby star systems, including some of Epsilon Eridani, Tau Ceti, Alpha Centauri B, Proxima Centauri, Sirius, and Procyon, but I don't see any specific approved programs for those yet.

Posted by: StargazeInWonder Mar 27 2023, 11:40 PM

Landmark result being reported today: TRAPPIST-1 b has no significant atmosphere. This has been determined by measurements of the dayside temperature made during secondary transits. The temperature of 500°K hints that no heat is moving from the dayside to the nightside. Note that TRAPPIST-1 b gets about 2/3 as much thermal radiation as Mercury, which has dayside temperatures of 700°K.

This doesn't mean that the cooler TRAPPIST-1 planets don't have atmospheres. It remains to be seen if it is only the high temperature of TRAPPIST-1 b that drove off any major atmosphere, or if the planets in the system all lost their atmospheres in the face of radiation / outbursts from their nearby star.

https://www.sciencenews.org/article/jwst-planet-trappist-1b-no-atmosphere

Posted by: StargazeInWonder Jun 1 2023, 11:19 PM

Further analysis of the TRAPPIST-1 b observations offer stronger constraints on any possible atmosphere, ruling out even a Mars-like atmosphere.

As far as surface conditions go, it appears that the closest solar system analogue to TRAPPIST-1 b, despite its larger-than-Earth size, is Mercury.

It will be interesting to see what Cycle 1 observations may have revealed about the other six planets in the system.

https://astrobiology.com/2023/05/constraining-the-thickness-of-the-atmosphere-of-trappist-1-b-from-its-jwst-secondary-eclipse-observation.html

Posted by: StargazeInWonder Jun 23 2023, 09:22 AM

The scorecard for TRAPPIST-1 is now Vacuums 2, Atmospheres 0. (At least substantial atmospheres.)

JWST observations for TRAPPIST-1 c's dayside is consistent with being quite a bit like the Moon, though a thin atmosphere hasn't been ruled out.

https://www.nature.com/articles/s41586-023-06232-z

I'm not sure which planet in the system we'll learn about next – the observation programs and methodologies vary – but this is sure playing out in interesting fashion, like a serialized drama.

Posted by: StargazeInWonder Sep 1 2023, 10:15 AM

This paper about LHS 475b almost certainly lends a clue as to why there have been JWST observations of several exoplanets that haven't yet led to publications summarizing those results: It's often going to be hard to reach specific conclusions, as the abstract explains, because of "the nature of the planet itself, rather than instrumental limits."

While the paper calls this planet "warm," it has an equilibrium temperature well above that of Mercury or Trappist-1b. This continues the streak that for terrestrial planets so hot, we have yet to confirm any atmosphere for any other them. In this case, however, no atmosphere has been ruled out.

https://www.nature.com/articles/s41550-023-02064-z

Posted by: Quetzalcoatl Sep 12 2023, 10:07 AM

Bonjour,

Interesting detection of atmospheric gases of a sub-Neptune in habitable zone. With a potential presence of Dimethyl sulfide (DMS) to be confirmed...

https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b

Posted by: Quetzalcoatl Oct 18 2023, 07:38 AM

Bonjour,

Webb Detects Tiny Quartz Crystals in the Clouds of a Hot Gas Giant

https://www.nasa.gov/missions/webb/webb-detects-tiny-quartz-crystals-in-the-clouds-of-a-hot-gas-giant/

Posted by: StargazeInWonder Oct 18 2023, 09:42 PM

There is the parable about someone looking for their lost keys under the light of streetlamps not because that is most likely where the keys were lost but because that's where light makes the search more feasible. In the current era of exoplanet characterization, planets that are large, hot, and/or close to their stars (and, of course, transiting) are not the only types of planet, and not the types we're most interested in, but they are the ones where JWST's capabilities make it possible to characterize them. It's fascinating, but also tantalizing as the candidate earthlike and habitable zone planets out there elude us for now.

I hope that, eg, Proxima b and the Tau Ceti planets lend themselves to characterization in the coming years, but it's clearly going to be a difficult challenge.

Posted by: Quetzalcoatl Nov 23 2023, 02:52 PM

Bonjour,

NASA’s Webb Identifies Methane In an Exoplanet’s Atmosphere,

https://blogs.nasa.gov/webb/2023/11/22/nasas-webb-identifies-methane-in-an-exoplanets-atmosphere/

Posted by: StargazeInWonder Nov 24 2023, 04:08 AM

It's interesting that methane has been elusive in exoplanet atmospheres studied so far. I suppose that this is because most exoplanets with atmospheres studied so far have been hot ones, causing photodissociation to occur at a high rate. I think that we'll be seeing a lot more characterization of "warm" exoplanets soon.

Posted by: StargazeInWonder Jan 5 2024, 08:12 PM

Another case of JWST finding that a hot terrestrial exoplanet shows no signs of a significant atmosphere. Probably not much of a surprise in this case, as the high density indicates not even a lot of silicates, much less volatiles.

https://astrobiology.com/2024/01/gj-367b-is-a-dark-hot-airless-sub-earth.html