HAT-P-70b through the Eyes of MAROON-X: Constraining Elemental Abundances of Metals and Insights on Atmosphere Dynamics

Journal article

Ultrahot Jupiters (UHJs) are exceptional laboratories for studying planetary atmospheres under extreme irradiation conditions. With close-in tidally locked orbits, these planets can have daysides hot enough for metals to be significantly ionized while still maintaining nightsides cold enough for refractory species to potentially condense. We present an analysis of the UHJ HAT-P-70b taken with the MAROON-X high-resolution spectrograph. Using cross correlations, we detect 14 neutral and singly ionized species, including Fe I, Fe II, Ti I, Ca I, Ca II, Cr I, Na I, V I, Mn I, Ni I, Mg I, Ba II, O I, and Sr I, with tentative evidence for H I, Co I, and K I. The absorption signals exhibit blueshifts on the order of a few kilometers per second, consistent with day-to-night winds. We further constrain relative abundances with atmospheric retrievals and demonstrate that some inferred elemental abundance ratios depend strongly on modeling assumptions. In particular, we show that a well-mixed retrieval approach neglecting ionization can strongly bias highly ionizable elements such as Ca and Ti. Accounting for the effects of equilibrium chemistry and thermal ionization generally results in inferred elemental abundance ratios that are closer to expectations for a solar-like composition, although not in all cases. Interestingly, we find a distinct nickel enrichment on HAT-P-70b, adding to the growing number of UHJ studies where the Ni abundance is seemingly enhanced. Our results underline the importance of considering physical and chemical atmospheric processes such as ionization when interpreting high-resolution transmission spectra of UHJs.

Authors: Sun, SL; Pelletier, S; Benneke, B; Prinoth, B; Parmentier, V

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: IOP Publishing
• Journal: The Astronomical Journal
• Volume: 172
• Issue: 1
• Pages: 9-9
• Publication date: 2026-06-03
• DOI: 10.3847/1538-3881/ae69d3
• EISSN: 1538-3881
• ISSN: 0004-6256
• Language: English
• Keywords: Planet; Astrochemistry; Abundance of the chemical elements; Hot Jupiter; Nickel; Ionization; Refractory (planetary science); Abundance (ecology); Absorption (acoustics); Atmosphere (unit)