Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST (2303.14849v2)

Abstract: 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 our own Solar System (Gillon et al. 2017). All TRAPPIST-1 planets have been observed with the transmission spectroscopy technique using the Hubble or Spitzer Space Telescopes, but no atmospheric features have been detected or strongly constrained (Ducrot et al. 2018; de Wit et al. 2018; Zhang et al. 2018; Garcia et al. 2022). TRAPPIST-1 b is the closest planet to the system's M dwarf star, and it receives 4 times as much irradiation 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 TRAPPIST-1 b exoplanet using the F1500W filter of the MIRI instrument on JWST. We detect the secondary eclipse in each of five separate observations with 8.7-$\sigma$ confidence when all data are combined. These measurements are most consistent with the re-radiation of the TRAPPIST-1 star's incident flux 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 from carbon dioxide (CO$_2$) or other species.

• The paper demonstrates JWST’s capability by detecting TRAPPIST-1 b’s thermal emission with an 8.7 sigma significance.
• It employs the MIRI instrument and the Eureka! pipeline to accurately measure secondary eclipse depths in the mid-infrared.
• The findings reveal a dayside brightness temperature of approximately 503K, suggesting negligible atmospheric heat redistribution or a sparse atmosphere.

An Analysis of TRAPPIST-1 b's Thermal Emission Using JWST Observations

Overview

This paper presents the paper of the Earth-sized exoplanet TRAPPIST-1 b using the James Webb Space Telescope (JWST), emphasizing its thermal characteristics derived through photometric secondary eclipse observations. The TRAPPIST-1 planetary system is distinguished by its seven Earth-sized planets, making it a focal point for investigating rocky exoplanets' atmospheres and surface conditions. Despite prior observations with instruments like the Hubble and Spitzer Space Telescopes, detection of significant atmospheric features on these planets has been elusive. Hence, this research marks a significant step in characterizing these alien worlds by identifying the thermal emission from TRAPPIST-1 b, thus providing insights into its atmospheric conditions.

Methodology

The JWST was utilized with the Mid-Infrared Instrument (MIRI) in observing five secondary eclipses of TRAPPIST-1 b through the F1500W filter. This filter, covering 13.5–16.6 micrometers, is optimal for capturing the thermal emission of TRAPPIST-1 b, which receives intense stellar irradiation. Data reduction employed the Eureka! pipeline, optimized for JWST's time-series data, aimed at minimizing noise and accurately measuring eclipse depths from the gathered light curves.

Key Findings

The paper detected TRAPPIST-1 b's secondary eclipses with a combined significance of 8.7 sigma, revealing a dayside brightness temperature of approximately 503 K (+26/-27 K). This is consistent with a model where the planet re-radiates incident stellar flux predominantly from its dayside, indicating a negligible atmospheric heat redistribution. This implies TRAPPIST-1 b either lacks a significant atmosphere, or its atmosphere is not effectively redistributing heat to the nightside. Moreover, the absence of carbon dioxide or other expected atmospheric absorbers suggests a lack of substantial atmosphere, potentially attributing prior transmission spectroscopy null results to atmospheric absence rather than obscuration by clouds or high molecular weight gases.

Discussion and Implications

The findings suggest TRAPPIST-1 b either lacks a dense atmosphere or has lost it over time due to stellar activity, common in M-dwarf systems like TRAPPIST-1. This loss could be driven by intense stellar winds and flares, which are known to affect atmospheric retention on such exoplanets. The paper's results are corroborated by theoretical models predicting complete atmospheric erosion in similar exoplanetary conditions, supporting the hypothesis that M-dwarf planets may generally have thin or absent atmospheres.

Understanding TRAPPIST-1 b's atmospheric characteristics has profound implications for the paper of exoplanet habitability and atmospheric evolution. The environmental extremes experienced by planets around M-dwarfs challenge assumptions made from solar system analogs, reinforcing the necessity for direct observations like those made with JWST.

Future Directions

Future research could aim to verify these findings with additional mid-infrared measurements and other observational strategies. JWST's capacity for high-resolution spectroscopy across additional wavelengths will be crucial in confirming the atmospheric composition or confirming its absence. Furthermore, similar studies on the other planets in the TRAPPIST-1 system could provide a comparative basis to assess atmospheric retention across planets with varying stellar proximities.

Overall, the successful observation of TRAPPIST-1 b’s thermal signature using JWST showcases the telescope’s potential in advancing our understanding of exoplanetary atmospheres, particularly for terrestrial-sized planets in M-dwarf systems. The continued application of such methodologies promises richer insights into the atmospheric properties and surface conditions necessary for assessing the habitability of rocky exoplanets in diverse stellar environments.