JWST and Exoplanet Atmospheres Options

[StargazeInWonder]

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.

[climber]

New technique to detect oxygen in exoplanet atmosphere :
https://astrobiology.nasa.gov/news/new-tech...inkId=167838838

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

[Mongo]

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

[Tom Tamlyn]

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

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:

This splendidly readable and authoritative book succeeds at the near-impossible task of explaining all you need to know about the revolutionary and fast-moving scientific field that's seeking out these new worlds and what may be lurking on them.

This post has been edited by Tom Tamlyn: Aug 26 2022, 02:46 PM

[climber]

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

[Mongo]

Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM

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.

Early Release Science of the Exoplanet WASP-39b with JWST NIRSpec G395H

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.

Early Release Science of the exoplanet WASP-39b with JWST NIRCam

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.

Early Release Science of the exoplanet WASP-39b with JWST NIRISS

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.

Direct Evidence of Photochemistry in an Exoplanet Atmosphere

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.

[Bill Harris]

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!

[Mongo]

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

[StargazeInWonder]

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."

[StargazeInWonder]

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.

[HSchirmer]

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.

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..."

[Hungry4info]

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.

[StargazeInWonder]

IIRC it also is selective for exoplanets with VERY short orbital periods- selection to observe multiple transits during the primary mission.

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.

[StargazeInWonder]

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.

[StargazeInWonder]

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-pl...b-no-atmosphere