The Thermal Emission Spectrum of the Nearby Rocky Exoplanet LTT 1445A b from JWST MIRI/LRS
The nearby transiting rocky exoplanet LTT 1445A b presents an ideal target for studying atmospheric retention in terrestrial planets orbiting M dwarfs. It is cooler than many rocky exoplanets yet tested for atmospheres, receiving a bolometric instellation similar to Mercury’s. Previous transmission spectroscopy ruled out a light H/He-dominated atmosphere but could not distinguish between a bare-rock, a high-MMW, or a cloudy atmosphere.
We present new secondary eclipse observations using JWST’s MIRI/LRS, covering the 5-12 μm range. From these observations, we detect a broadband secondary eclipse depth of 41 ± 9 ppm and measure a mid-eclipse timing consistent with a circular orbit (at 1.7σ). From its emission spectrum, the planet’s dayside brightness temperature is constrained to 525 ± 15 K, yielding a temperature ratio relative to the maximum average dayside temperature from instant thermal reradiation by a rocky surface R = Tday,obs/Tmax = 0.952 ± 0.057, consistent with emission from a dark rocky surface.
From an energy balance perspective, such a warm dayside temperature disfavors thick atmospheres, excluding ∼100 bar atmospheres with Bond albedo > 0.08 at the 3σ level. Furthermore, forward modeling of atmospheric emission spectra disfavor simple 100% CO2 atmospheres with surface pressures of 1, 10, and 100 bar at 4.2σ, 6.6σ, and 6.8σ confidence, respectively.
These results suggest that LTT 1445A b lacks a very thick CO2 atmosphere, possibly due to atmospheric erosion driven by stellar activity. However, the presence of a moderately thin atmosphere (similar to those on Mars, Titan, or Earth) remains uncertain.
Spectroscopic light curves from first, second and third visits (top to bottom) from the Eureka! (left panel) and SPARTA (middle panel) pipelines binned to wavelength resolution of 0.1 µm and time resolution of 1 minute for better visualization. The ratio between the two pipeline products (SPARTA/Eureka) is shown in the right panel. Each white tick at the top and bottom of each plot indicates the end of each segment of data. Solid vertical red lines indicate 20 minutes of trimming applied to all visits. In visit 3 a clear flux offset is seen near -0.06 days (red arrow), so we trim an addition 50 minutes to avoid it. Dashed horizontal orange lines indicate the edges of each wavelength bin in 20 bins scheme. The planet’s eclipse is too shallow to see with this colorbar. — astro-ph.EP
Patcharapol Wachiraphan, Zachory K. Berta-Thompson, Hannah Diamond-Lowe, Jennifer G. Winters, Catriona Murray, Michael Zhang, Qiao Xue, Caroline V. Morley, Marialis Rosario-Franco, Girish M. Duvvuri
Comments: 31 pages, 14 figures, submitted to AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2410.10987 [astro-ph.EP] (or arXiv:2410.10987v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2410.10987
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From: Patcharapol Wachiraphan
[v1] Mon, 14 Oct 2024 18:15:19 UTC (1,912 KB)
https://arxiv.org/abs/2410.10987
Astrobiology,
