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Researchers analyzed the atmosphere of ultra-hot Jupiter MASCARA-1b using high-resolution spectroscopy and detected seven chemical species including water, carbon monoxide, and several metals. The planet's atmosphere shows solar-level overall metallicity but contains approximately 2.5 times more refractory (rock-forming) elements than the host star, with a refractory-to-volatile ratio about 2.3 times solar values. These measurements suggest the planet formed by accreting material between the soot-water or water-carbon monoxide ice lines in the protoplanetary disk.
Why it matters
This represents the most complete atmospheric chemical inventory of MASCARA-1b to date and provides critical constraints on giant planet formation theories. The methodology and findings establish a framework for understanding where and how gas giant planets accumulate their atmospheres, which will be applied to larger samples of exoplanets observed with next-generation telescopes.
arXiv:2606.07497v1 Announce Type: new
Abstract: Ultra-hot Jupiters (UHJs; $T_{rm eq} gtrsim 2000$ 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 ($T_{rm eq} approx 2600$ K) using the IGRINS and IGRINS-2 spectrographs. We detect robust (SNR$>$4) signals from H$_2$O, 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 $approx$0.2 dex, retrieving a solar atmospheric metallicity ([M/H]$_odot$ $= 0.07^{+0.17}_{-0.13}$ $approx 1.2times$ 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]$_odot$ $= 0.40^{+0.23}_{-0.17} approx 2.5times$ solar; $approx 3.8times$ stellar), and a moderately super-solar refractory-to-volatile ratio ([R/V]$_odot$ $= 0.36^{+0.11}_{-0.09}$ $approx 2.3times$ solar). Comparison with formation models suggests that MASCARA-1b most likely accreted material between the soot-H$_2$O or H$_2$O-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.