Analyzing Atmospheric Temperature Profiles and Spectra of M Dwarf Rocky Planets

Malik, Matej; Kempton, Eliza M.-R.; Koll, Daniel D. B.; Mansfield, Megan; Bean, Jacob L.; Kite, Edwin S.

doi:10.3847/1538-4357/ab4a05

Cited by 50 publications

(44 citation statements)

References 101 publications

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“… 2019 ; Malik et al. 2019 ), depending on the atmospheric composition and pressure of the planet. These promising results motivated two Guaranteed Time Observations (GTO) programs on JWST (GTO 1279, PI: Pierre-Olivier Lagage; GTO 1177, PI: Thomas Greene) to observe 10 secondary eclipses of TRAPPIST-1b with MIRI in imager mode.…”

Section: Future Prospectsmentioning

confidence: 99%

A Review of Possible Planetary Atmospheres in the TRAPPIST-1 System

et al. 2020

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TRAPPIST-1 is a fantastic nearby (∼39.14 light years) planetary system made of at least seven transiting terrestrial-size, terrestrial-mass planets all receiving a moderate amount of irradiation. To date, this is the most observationally favourable system of potentially habitable planets known to exist. Since the announcement of the discovery of the TRAPPIST-1 planetary system in 2016, a growing number of techniques and approaches have been used and proposed to characterize its true nature. Here we have compiled a state-of-the-art overview of all the observational and theoretical constraints that have been obtained so far using these techniques and approaches. The goal is to get a better understanding of whether or not TRAPPIST-1 planets can have atmospheres, and if so, what they are made of. For this, we surveyed the literature on TRAPPIST-1 about topics as broad as irradiation environment, planet formation and migration, orbital stability, effects of tides and Transit Timing Variations, transit observations, stellar contamination, density measurements, and numerical climate and escape models. Each of these topics adds a brick to our understanding of the likely—or on the contrary unlikely—atmospheres of the seven known planets of the system. We show that (i) Hubble Space Telescope transit observations, (ii) bulk density measurements comparison with H 2 -rich planets mass-radius relationships, (iii) atmospheric escape modelling, and (iv) gas accretion modelling altogether offer solid evidence against the presence of hydrogen-dominated—cloud-free and cloudy—atmospheres around TRAPPIST-1 planets. This means that the planets are likely to have either (i) a high molecular weight atmosphere or (ii) no atmosphere at all. There are several key challenges ahead to characterize the bulk composition(s) of the atmospheres (if present) of TRAPPIST-1 planets. The main one so far is characterizing and correcting for the effects of stellar contamination. Fortunately, a new wave of observations with the James Webb Space Telescope and near-infrared high-resolution ground-based spectrographs on existing very large and forthcoming extremely large telescopes will bring significant advances in the coming decade.

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Section: Future Prospectsmentioning

confidence: 99%

A Review of Possible Planetary Atmospheres in the TRAPPIST-1 System

et al. 2020

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“…Thanks to their small size, mass, and luminosity combined with their relatively large infrared brightness, the nearest ultracool dwarf stars (spectral types M7 and later) represent promising targets for the detailed study of potentially habitable transiting exoplanets with upcoming giant telescopes such as JWST or ELTs (Kaltenegger & Traub 2009;Malik et al 2019;Mansfield et al 2019;Koll 2019). This fact motivated the development of the new ground-based transit survey called the Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS).…”

Section: Introductionmentioning

confidence: 99%

TRAPPIST-1: Global results of theSpitzerExploration Science Program Red Worlds

Ducrot

Gillon

Delrez

et al. 2020

A&A

112

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Context. With more than 1000 h of observation from Feb. 2016 to Oct. 2019, the Spitzer Exploration Program Red Worlds (ID: 13067, 13175 and 14223) exclusively targeted TRAPPIST-1, a nearby (12 pc) ultracool dwarf star, finding that it is orbited by seven transiting Earth-sized planets. At least three of these planets orbit within the classical habitable zone of the star, and all of them are well-suited for a detailed atmospheric characterization with the upcoming JWST. Aims. The main goals of the Spitzer Red Worlds program were (1) to explore the system for new transiting planets, (2) to intensively monitor the planets’ transits to yield the strongest possible constraints on their masses, sizes, compositions, and dynamics, and (3) to assess the infrared variability of the host star. In this paper, we present the global results of the project. Methods. We analyzed 88 new transits and combined them with 100 previously analyzed transits, for a total of 188 transits observed at 3.6 or 4.5 μm. For a comprehensive study, we analyzed all light curves both individually and globally. We also analyzed 29 occultations (secondary eclipses) of planet b and eight occultations of planet c observed at 4.5 μm to constrain the brightness temperatures of their daysides. Results. We identify several orphan transit-like structures in our Spitzer photometry, but all of them are of low significance. We do not confirm any new transiting planets. We do not detect any significant variation of the transit depths of the planets throughout the different campaigns. Comparing our individual and global analyses of the transits, we estimate for TRAPPIST-1 transit depth measurements mean noise floors of ~35 and 25 ppm in channels 1 and 2 of Spitzer/IRAC, respectively. We estimate that most of this noise floor is of instrumental origins and due to the large inter-pixel inhomogeneity of IRAC InSb arrays, and that the much better interpixel homogeneity of JWST instruments should result in noise floors as low as 10 ppm, which is low enough to enable the atmospheric characterization of the planets by transit transmission spectroscopy. Our analysis reveals a few outlier transits, but we cannot conclude whether or not they correspond to spot or faculae crossing events. We construct updated broadband transmission spectra for all seven planets which show consistent transit depths between the two Spitzer channels. Although we are limited by instrumental precision, the combined transmission spectrum of planet b to g tells us that their atmospheres seem unlikely to be CH4-dominated. We identify and model five distinct high energy flares in the whole dataset, and discuss our results in the context of habitability. Finally, we fail to detect occultation signals of planets b and c at 4.5 μm, and can only set 3-σ upper limits on their dayside brightness temperatures (611 K for b 586 K for c).

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“…Detection of a temperature inversion in exoplanetary atmospheres is particularly valuable (e.g., Crossfield 2015; Madhusudhan 2019; Malik et al 2019). With a few exceptions, temperatures in the upper troposphere and lower stratosphere were retrieved with deviations from the true profiles mostly smaller than 10 K. For the "failed fits" (i.e., Earth atmospheres #16 and #31 in SW-TIR) the estimated tropopause minimum was substantially too small (however, the fits were much better with an enlarged fitting window) but, nevertheless, the shape was correct and the inversion was detected.…”

Section: Discussionmentioning

confidence: 99%

SVEEEETIES: singular vector expansion to estimate Earth-like exoplanet temperatures from infrared emission spectra

Schreier

Städt

Wunderlich

et al. 2020

A&A

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Context. Detailed characterizations of exoplanets are clearly moving to the forefront of planetary science. Temperature is a key marker for understanding atmospheric physics and chemistry. Aims. We aim to retrieve temperatures of N 2 -O 2 dominated atmospheres from secondary eclipse spectroscopic observations of the thermal emission of Earth-like exoplanets orbiting G-, K-, and M-stars, using large-aperture future space telescopes. Methods. A line-by-line radiative transfer code was used to generate synthetic thermal infrared (TIR) observations. The atmospheric temperature is approximated by an expansion with the base vectors defined by a singular value decomposition of a matrix comprising representative profiles. A nonlinear least squares fitting was used to estimate the unknown expansion coefficients. Results. Analysis of the 4.3 µm and 15 µm CO 2 bands in the TIR spectra permits the inference of temperatures even for low signalto-noise ratios (S/N) of 5 at medium resolution. Deviations from the true temperature in the upper troposphere and lower-to-mid stratosphere are usually in the range of a few Kelvin, with larger deviations in the upper atmosphere and, less often, in the lower troposphere. Although the performance of the two bands is equivalent in most cases, the longwave TIR is more favorable than the shortwave due to increased star-planet contrast. A high spectral resolution, as provided by the James Webb Space Telescope (JWST) instruments, is important for retaining sensitivity to the upper atmosphere. Furthermore, the selection of an appropriate set of base functions is also key. Conclusions. Temperature in the mid-atmosphere, relevant for understanding habitability, can be suitably characterized by infrared emission spectroscopy with a resolution of at least 1000 (ideally ≈2500). Obtaining the necessary S/N will be challenging even for JWST, however, it could be feasible with future space missions, such as the Origins Space Telescope or the Large Interferometer for Exoplanets. In the meantime, a least squares fitting with an appropriate set of base functions is also applicable for other classes of planets.

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Analyzing Atmospheric Temperature Profiles and Spectra of M Dwarf Rocky Planets

Cited by 50 publications

References 101 publications

A Review of Possible Planetary Atmospheres in the TRAPPIST-1 System

A Review of Possible Planetary Atmospheres in the TRAPPIST-1 System

TRAPPIST-1: Global results of theSpitzerExploration Science Program Red Worlds

SVEEEETIES: singular vector expansion to estimate Earth-like exoplanet temperatures from infrared emission spectra

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