Atmospheres & Climate

CO, H2O, And CH4 In The Dusty Atmosphere Of A ≤5 Myr-old Exoplanet

By Keith Cowing
Status Report
August 30, 2023
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CO, H2O, And CH4 In The Dusty Atmosphere Of A ≤5 Myr-old Exoplanet
𝐻-band (top) and 𝐾-band (bottom) spectra of 2M0437b. The dark blue points are the reduced spectrum produced by the OSIRIS pipeline, the dark blue line is the 21-point running median, the magenta curve is a model of the spectrum to further correct for telluric absorption using a spectrum of an A0 star, and the green points and line are the corrected spectrum and its 21-point running median. The grey line is a model transmission spectrum for the atmosphere over Maunakea for an airmass of 1.5 and water vapor column of 1.6 mm (courtsey Gemini Orbservatory, Lord 1992). The absorption functions of key molecules (H2O, CO, CH4, HCN) computed using the HITRAN database (Mikhailenko et al. 2005; Gordon et al. 2022) and normalized by the maximum for that molecule in each bandpass are plotted at the top (blue, black, red, and orange lines, respectively. The vertical dotted lines mark H Brackett lines and the Na I doublet, and spectral features of molecules of interest are labeled. — astro-ph.EP

Very young massive planets are sufficiently luminous by their internal heat of formation to permit detailed studies, including spectroscopy of their atmospheres with large telescopes at sufficient resolution (λ/Δλ≳1000) to identify major constituents to inform models of planet formation and early evolution.

We obtained 1-2.4μm (YJHK) spectra of the planetary-mass “b” companion of 2MASS~J04372171+2651014, a 1-3 Myr-old M dwarf member of the Taurus star-forming region, and one of the youngest such objects discovered to date. These indicate the presence of CO and possibly H2O and CH4 in the atmosphere, all suggesting a Teff of around 1200K, characteristic of a L-T transition spectral type and consistent with previous estimates based on its luminosity and age.

The absence or attenuation of spectral features at shorter wavelengths suggests the presence of micron-size dust, consistent with the object’s red color. The spectrum of 2M0437b resembles those of the HR 8799 planets, especially the innermost “b” planet, with the exception of a pronounced flux deficit in the H-band of uncertain origin.

Eric Gaidos, Teruyuki Hirano

Comments: accepted to MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2308.13745 [astro-ph.EP] (or arXiv:2308.13745v1 [astro-ph.EP] for this version)
Submission history
From: Eric Gaidos
[v1] Sat, 26 Aug 2023 03:11:22 UTC (1,615 KB)
Astrobiology, Astrochemistry,

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