Exoplanets, -moons, -comets

The Roasting Marshmallows Program with IGRINS on Gemini South V: Atmosphere of MASCARA-1b is Enriched in Refractory Elements

By Keith Cowing
Press Release
June 10, 2026
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The Roasting Marshmallows Program with IGRINS on Gemini South V: Atmosphere of MASCARA-1b is Enriched in Refractory Elements
Summary of our observations and detrending process. Left inset shows the phase coverage of our observations in pre-secondary eclipse (pink) and post-secondary eclipse (yellow) geometries. The phase range obstructed by the secondary eclipse is shown as the thick black line between these geometries. In the top right panel, we show our median signal-to-noise ratios (SNRs) per order for pre-eclipse (pink) and post-eclipse (yellow) datasets. IGRINS and IGRINS-2 offer near-identical wavelength coverage in H and K bands. Due to better observing conditions, our post-eclipse dataset has a higher SNR than the pre-eclipse observations. In the bottom panels to the right, we show the raw data and post-SVD residual data (bottom) from an H-band order with heavy telluric contamination. The transmittance spectrum of Earth’s atmosphere is shown in the background of top SNR panel. The white regions in the residual data are the masked wavelengths where there is high telluric contamination. — astro-ph.EP

Ultra-hot Jupiters (UHJs; Teq≳2000 K) enable simultaneous detection of volatile (ice-forming) and refractory (rock-forming) species in planetary atmospheres, providing a powerful diagnostic of planet formation and atmospheric processing.

We present a comprehensive high-resolution cross-correlation spectroscopy (HRCCS) analysis of the UHJ MASCARA-1b (Teq≈2600 K) using the IGRINS and IGRINS-2 spectrographs. We detect robust (SNR>4) signals from H2O, CO, OH, Fe I, Mg I, Ca I, and Ti I, marking the most complete atmospheric inventory of MASCARA-1b to date.

Using a chemically consistent atmospheric inference framework, we constrain elemental abundances to a typical precision of ≈0.2 dex, retrieving a solar atmospheric metallicity ([M/H]⊙ =0.07+0.17−0.13 ≈1.2× solar), a C/O ratio (C/O =0.65+0.08−0.08) consistent with solar value (C/O = 0.59), an enhanced refractory abundance ([R/H]⊙ =0.40+0.23−0.17≈2.5× solar; ≈3.8× stellar), and a moderately super-solar refractory-to-volatile ratio ([R/V]⊙ =0.36+0.11−0.09 ≈2.3× solar).

Comparison with formation models suggests that MASCARA-1b most likely accreted material between the soot-H2O or H2O-CO snowlines (at 68% confidence). We additionally find stellar values for atmospheric Ti/Mg and Ca/Mg ratios (at 68% confidence). The Mg/Fe is also found to be consistent with stellar value at 95% confidence.

Therefore, we do not find strong indication of nightside cold trapping in MASCARA-1b. As homogeneous refractory-to-volatile measurements expand across the UHJ population, particularly with upcoming Extremely Large Telescopes, these diagnostics will enable statistically robust tests of emerging trends in giant planet formation and atmospheric evolution.

Krishna Kanumalla, Michael R. Line, Martina Chiarella, Matteo Brogi, Peter C. B. Smith, Jorge A. Sanchez, Yayaati Chachan, Joshua Lothringer, Joost P. Wardenier, Hayley Beltz, Carlos Saffe, Emily K. Deibert, Megan Weiner Mansfield, Stefan Pelletier, Vivien Parmentier, Yeon-ho Choi, Swaetha Ramkumar, Arjun B. Savel, Luis Welbanks, Jacob L. Bean, Vatsal Panwar, Tomás Azevedo Silva, Lorenzo Pino, Yuya Hayashi, Dongwook Lim, Cicero X. Lu, Venu M. Kalari, Teo Močnik, Mark G. Rawlings, Heeyoung Oh, Ruben J. Diaz, Chan Park, Jae-Joon Lee, Sanghyuk Kim, Ueejeong Jeong, Hye-In Lee, Woojin Park, Youngsam Yu, Yunjong Kim, Moo-Young Chun, Jae Sok Oh, Sungho Lee, Jeong-Gyun Jang, Bi-Ho Jang, Hyeon Cheol Seong, Hyun-Jeong Kim, Cynthia B. Brooks, Gregory N. Mace, Hanshin Lee, John M. Good, Daniel T. Jaffe, Kang-Min Kim, In-Soo Yuk, Narae Hwang, Byeong-Gon Park, Hwihyun Kim, Brian Chinn, Francisco Ramos, Pablo Prado, John White, Andres Olivares, Valentina Oyarzun, Emma Kurz, Hawi Stecher, Carlos Quiroz, Ignacio Arriagada, Thomas L. Hayward, Hyewon Suh, Jen Miller, Siyi Xu, Emanuele Paolo Farina, Charlie Figura, Andrew Stephens, Bryan Miller, Kathleen Labrie, Paul Hirst, Edo Tapia, Zachary Hartmann

Comments: 20 pages, 12 figures, accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2606.07497 [astro-ph.EP] (or arXiv:2606.07497v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2606.07497
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Related DOI:
https://doi.org/10.3847/1538-3881/ae77f1
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Submission history
From: Krishna Kanumalla
[v1] Fri, 5 Jun 2026 17:52:08 UTC (12,028 KB)
https://arxiv.org/abs/2606.07497

Astrobiology, exoplanet,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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