Exoplanetology: Exoplanets & Exomoons

JWST Thermal Emission of the Terrestrial Exoplanet GJ 1132b

By Keith Cowing
Press Release
August 28, 2024
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JWST Thermal Emission of the Terrestrial Exoplanet GJ 1132b
Goodness-of-fit (χ 2 ) of the eclipse depths of the suite of atmospheric models, plotted as functions of the modeled surface pressure. The best-fit blackbody (691 K) to the emission spectrum is shown with the black dashed line. The bare surface models are shown in the leftmost column with diamonds. The median and 1-σ and 2-σ equivalent quantiles of the χ 2 distribution (k=14, k is the degree of freedom) are shown as the solid black line, the dark gray band, and the light gray band, respectively. The atmosphere models with compositions of CO2 filled with O2 are shown with squares and H2O filled with O2 are shown with circles, where colors indicate the percentage of trace gasses. The atmosphere models generally move, from the thinnest (10−4 bar) to the thickest (102 bar) surface pressures, from the χ 2 for the maximally hot temperature (blue dashed line) to the χ 2 for the equilibrium temperature (red dashed line), with deviating inflection points arising due to spectral features in the LRS bandpass and changes in the temperaturepressure profile. Atmospheric models that produce χ 2 values comparable to the best-fit blackbody are plotted in Figure 6. — astro-ph.EP

We present thermal emission measurements of GJ 1132b spanning 5–12 um obtained with the Mid-Infrared Instrument Low-Resolution Spectrometer (MIRI/LRS) on the James Webb Space Telescope (JWST).

GJ 1132b is an M-dwarf rocky planet with Teq=584 K and an orbital period of 1.6 days. We measure a white-light secondary eclipse depth of 140+/-17 ppm, which corresponds to a dayside brightness temperature of Tp,dayside= 709+/-31 K using improved star and planet parameters.

This measured temperature is only 1 sigma below the maximum possible dayside temperature of a bare rock (i.e., assuming a zero albedo planet with no heat redistribution, Tmax = 746+14/-11 K).

The emission spectrum is consistent with a featureless blackbody, which agrees with a wide range of possible surface compositions. By comparing forward models to the dayside emission spectrum, we rule out Earth-thickness (P ~ 1 bar) atmospheres with at least 1% H2O, atmospheres of any modeled thickness (10^-4 — 10^2 bar) that contain at least 1% CO2, and thick, Venus-like atmospheres (P>~100 bar) with at least 1 ppm CO2 or H2O.

We therefore conclude that GJ 1132b likely does not have a significant atmosphere. This finding supports the concept of a universal ‘Cosmic Shoreline’ given the high level of bolometric and XUV irradiation received by the planet.

GJ 1132b in the context of the Cosmic Shoreline (Zahnle & Catling 2017). In the solar system, the dashed blue line separates bodies that have atmospheres from those that don’t. Blue shading illustrates uncertainty on the y-axis. For exoplanets, only rocky planets around M-dwarfs with thermal emission measurements are shown. — astro-ph.EP

Qiao Xue, Jacob L. Bean, Michael Zhang, Alexandra S. Mahajan, Jegug Ih, Jason D. Eastman, Jonathan I. Lunine, Megan Weiner Mansfield, Brandon P. Coy, Eliza M.-R. Kempton, Daniel D. Koll, Edwin S. Kite

Comments: Accepted by ApJL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2408.13340 [astro-ph.EP] (or arXiv:2408.13340v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2408.13340
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Submission history
From: Qiao Xue
[v1] Fri, 23 Aug 2024 19:20:15 UTC (20,178 KB)
https://arxiv.org/abs/2408.13340

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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