We have collected transit times for the TRAPPIST-1 system with the Spitzer Space Telescope over four years. We add to these ground-based, HST, and K2 transit-time measurements, and revisit an N-body ...dynamical analysis of the seven-planet system using our complete set of times from which we refine the mass ratios of the planets to the star. We next carry out a photodynamical analysis of the Spitzer light curves to derive the density of the host star and the planet densities. We find that all seven planets' densities may be described with a single rocky mass-radius relation which is depleted in iron relative to Earth, with Fe 21 wt% versus 32 wt% for Earth, and otherwise Earth-like in composition. Alternatively, the planets may have an Earth-like composition but enhanced in light elements, such as a surface water layer or a core-free structure with oxidized iron in the mantle. We measure planet masses to a precision of 3%-5%, equivalent to a radial-velocity (RV) precision of 2.5 cm s−1, or two orders of magnitude more precise than current RV capabilities. We find the eccentricities of the planets are very small, the orbits are extremely coplanar, and the system is stable on 10 Myr timescales. We find evidence of infrequent timing outliers, which we cannot explain with an eighth planet; we instead account for the outliers using a robust likelihood function. We forecast JWST timing observations and speculate on possible implications of the planet densities for the formation, migration, and evolution of the planet system.
Abstract Atmospheric pollutants such as chlorofluorocarbons and NO 2 have been proposed as potential remotely detectable atmospheric technosignature gases. Here we investigate the potential for ...artificial greenhouse gases including CF 4 , C 2 F 6 , C 3 F 8 , SF 6 , and NF 3 to generate detectable atmospheric signatures. In contrast to passive incidental by-products of industrial processes, artificial greenhouse gases would represent an intentional effort to change the climate of a planet with long-lived, low-toxicity gases and would possess low false positive potential. An extraterrestrial civilization may be motivated to undertake such an effort to arrest a predicted snowball state on their home world or to terraform an otherwise uninhabitable terrestrial planet within their system. Because artificial greenhouse gases strongly absorb in the thermal mid-infrared window of temperate atmospheres, a terraformed planet will logically possess strong absorption features from these gases at mid-infrared wavelengths (∼8–12 μ m), possibly accompanied by diagnostic features in the near-infrared. As a proof of concept, we calculate the needed observation time to detect 1 10(100) ppm of C 2 F 6 /C 3 F 8 /SF 6 on TRAPPIST-1 f with JWST MIRI’s Low Resolution Spectrometer (LRS) and NIRSpec. We find that a combination of 110(100) ppm each of C 2 F 6 , C 3 F 8 , and SF 6 can be detected with a signal-to-noise ratio ≧ 5 in as few as 2510(5) transits with MIRI/LRS. We further explore mid-infrared direct-imaging scenarios with the Large Interferometer for Exoplanets mission concept and find these gases are more detectable than standard biosignatures at these concentrations. Consequently, artificial greenhouse gases can be readily detected (or excluded) during normal planetary characterization observations with no additional overhead.
Abstract
The first James Webb Space Telescope observations of TRAPPIST-1 c showed a secondary eclipse depth of 421 ± 94 ppm at 15
μ
m, which is consistent with a bare rock surface or a thin, O
2
...-dominated, low-CO
2
atmosphere. Here we further explore potential atmospheres for TRAPPIST-1 c by comparing the observed secondary eclipse depth to synthetic spectra of a broader range of plausible environments. To self-consistently incorporate the impact of photochemistry and atmospheric composition on atmospheric thermal structure and predicted eclipse depth, we use a two-column climate model coupled to a photochemical model and simulate O
2
-dominated, Venus-like, and steam atmospheres. We find that a broader suite of plausible atmospheric compositions are also consistent with the data. For lower-pressure atmospheres (0.1 bar), our O
2
–CO
2
atmospheres produce eclipse depths within 1
σ
of the data, consistent with the modeling results of Zieba et al. However, for higher-pressure atmospheres, our models produce different temperature–pressure profiles and are less pessimistic, with 1–10 bar O
2
, 100 ppm CO
2
models within 2.0
σ
–2.2
σ
of the measured secondary eclipse depth and up to 0.5% CO
2
within 2.9
σ
. Venus-like atmospheres are still unlikely. For thin O
2
atmospheres of 0.1 bar with a low abundance of CO
2
(∼100 ppm), up to 10% water vapor can be present and still provide an eclipse depth within 1
σ
of the data. We compared the TRAPPIST-1 c data to modeled steam atmospheres of ≤3 bars, which are 1.7
σ
–1.8
σ
from the data and not conclusively ruled out. More data will be required to discriminate between possible atmospheres or more definitively support the bare rock hypothesis.
Abstract A comprehensive infrared spectroscopic study of star TRAPPIST-1 is a crucial step toward the detailed examination of its planets. While the presence of Earth’s atmosphere has limited the ...spectral extent of such a study up to now, the Near Infrared Imager and Slitless Spectrograph (NIRISS) and the Near Infrared Spectrograph instruments aboard the James Webb Space Telescope (JWST) can now yield the 0.6–5 μ m spectral energy distribution (SED) of the star. Here we translate TRAPPIST-1's SED into tight constraints on its luminosity ( L bol = 0.000566 ± 0.000022 L ⊙ ), effective temperature ( T eff = 2569 ± 28 K), and metallicity (Fe/H = 0.052 ± 0.073) and investigate the behavior of its gravity-sensitive indices. Through band-by-band comparisons of the NIRISS and ground-based spectra, TRAPPIST-1 exhibits a blend of both field source and intermediate-gravity spectral characteristics, suggesting that the star is likely a field-age source with spectral features reminiscent of young objects. We also employ photospheric modeling incorporating theoretical and JWST spectra to constrain stellar surface heterogeneities, finding that the limited fidelity of current stellar spectral models precludes definitive constraints on the physical parameters of the distinct spectral components giving rise to TRAPPIST-1's photospheric heterogeneity and variability. In addition, we find intermodel differences in the inferences of properties (e.g., the effective temperature) over one order of magnitude larger than the instrument-driven uncertainties (∼100 K vs. ∼4 K), pointing toward a model-driven accuracy wall. Our findings call for a new generation of stellar models to support the optimal mining of JWST data and further constraining stellar—and ultimately planetary—properties.
We apply the transit light curve self-contamination technique of Morris et al. to search for the effect of stellar activity on the transits of the ultracool dwarf TRAPPIST-1 with 2018 Spitzer ...photometry. The self-contamination method fits the transit light curves of planets orbiting spotted stars, allowing the host star to be a source of contaminating positive or negative flux that influences the transit depths but not the ingress/egress durations. We find that none of the planets show statistically significant evidence for self-contamination by bright or dark regions of the stellar photosphere. However, we show that small-scale magnetic activity, analogous in size to the smallest sunspots, could still be lurking undetected in the transit photometry.
ABSTRACT
To reduce and analyse astronomical images, astronomers can rely on a wide range of libraries providing low-level implementations of legacy algorithms. However, combining these routines into ...robust and functional pipelines requires a major effort that often ends up in instrument-specific and poorly maintainable tools, yielding products that suffer from a low level of reproducibility and portability. In this context, we present prose, a python framework to build modular and maintainable image processing pipelines. Built for astronomy, it is instrument-agnostic and allows the construction of pipelines using a wide range of building blocks, pre-implemented or user-defined. With this architecture, our package provides basic tools to deal with common tasks, such as automatic reduction and photometric extraction. To demonstrate its potential, we use its default photometric pipeline to process 26 TESS candidates follow-up observations and compare their products to the ones obtained with AstroImageJ, the reference software for such endeavours. We show that prose produces light curves with lower white and red noise while requiring less user interactions and offering richer functionalities for reporting.
Not so long ago we could still believe that our solar system was unique, that the planets surrounding our Sun were exceptions and that life only exists on planet Earth. Since the first discovery of ...an exoplanet (a planet orbiting a different star than the sun) in 1995 1 our views changed drastically. First of all, we realised that hosting planets is more likely a rule for a star than an exception. Second, we discovered a large diversity of systems with extraordinary structure and history. In particular, we realised that the majority of planets discovered belong to a class of planets that does not even exist in our system. To date, we count more than 4000 confirmed exoplanets with almost one new planet being discovered every two days. In this article we review the detection and first characterisation of an exceptional system, the TRAPPIST-1 system. We explain what makes this system so special and all the work that has been archived since the first announcement of its discovery in 2015.
Il n’y a pas si longtemps, nous pouvions encore croire que notre système solaire était unique, que les planètes entourant notre Soleil étaient des exceptions et que la vie n’existe que sur la planète Terre. Depuis la première découverte d’une exoplanète (une planète en orbite autour d’une étoile différente du soleil) en 1995, nos vues ont changé radicalement. Tout d’abord, nous avons réalisé que l’hébergement des planètes est plus probablement une règle pour une étoile qu’une exception. Deuxièmement, nous avons découvert une grande diversité de systèmes avec une structure et une histoire extraordinaires. En particulier, nous avons réalisé que la majorité des planètes découvertes appartiennent à une classe de planètes qui n’existe même pas dans notre système. À ce jour, nous comptons plus de 4000 exoplanètes confirmées, avec presque une nouvelle planète découverte tous les deux jours. Dans cet article, nous passons en revue la détection et la première caractérisation d’un système exceptionnel, le système TRAPPIST-1. Nous expliquons ce qui rend ce système si spécial et tout le travail qui a été archivé depuis la première annonce de sa découverte en 2015.
The TRAPPIST-1 system is remarkable for its seven planets that are similar in size, mass, density and stellar heating to the rocky planets Venus, Earth and Mars in the Solar System
. All the ...TRAPPIST-1 planets have been observed with transmission spectroscopy using the Hubble or Spitzer space telescopes, but no atmospheric features have been detected or strongly constrained
. TRAPPIST-1 b is the closest planet to the M-dwarf star of the system, and it receives four times as much radiation as Earth receives from the Sun. This relatively large amount of stellar heating suggests that its thermal emission may be measurable. Here we present photometric secondary eclipse observations of the Earth-sized exoplanet TRAPPIST-1 b using the F1500W filter of the mid-infrared instrument on the James Webb Space Telescope (JWST). We detect the secondary eclipses in five separate observations with 8.7σ confidence when all data are combined. These measurements are most consistent with re-radiation of the incident flux of the TRAPPIST-1 star from only the dayside hemisphere of the planet. The most straightforward interpretation is that there is little or no planetary atmosphere redistributing radiation from the host star and also no detectable atmospheric absorption of carbon dioxide (CO
) or other species.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
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