JWST and Exoplanet Atmospheres |
JWST and Exoplanet Atmospheres |
Sep 14 2021, 05:44 PM
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#1
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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. |
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Jan 2 2022, 11:01 PM
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#2
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Member Group: Members Posts: 723 Joined: 13-June 04 Member No.: 82 |
The JWST General Observer Programs in Cycle 1 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
Attached File(s)
1743.pdf ( 24.08K )
Number of downloads: 1724
2420.pdf ( 30.33K ) Number of downloads: 412 2304.pdf ( 26.98K ) Number of downloads: 368 1952.pdf ( 22.62K ) Number of downloads: 378 1981.pdf ( 75.07K ) Number of downloads: 365 2589.pdf ( 49.27K ) Number of downloads: 558 2512.pdf ( 114.16K ) Number of downloads: 639 |
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Jan 3 2022, 01:09 AM
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#3
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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. |
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