High Tide or Riptide on the Cosmic Shoreline? A Water-Rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ~486b from JWST Observations

Autor: Moran, Sarah E., Stevenson, Kevin B., Sing, David K., MacDonald, Ryan J., Kirk, James, Lustig-Yaeger, Jacob, Peacock, Sarah, Mayorga, L. C., Bennett, Katherine A., López-Morales, Mercedes, May, E. M., Rustamkulov, Zafar, Valenti, Jeff A., Redai, Jéa I. Adams, Alam, Munazza K., Batalha, Natasha E., Fu, Guangwei, Gonzalez-Quiles, Junellie, Highland, Alicia N., Kruse, Ethan, Lothringer, Joshua D., Ceballos, Kevin N. Ortiz, Sotzen, Kristin S., Wakeford, Hannah R.
Rok vydání: 2023
Předmět:
Druh dokumentu: Working Paper
DOI: 10.3847/2041-8213/accb9c
Popis: Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars' highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8-5.2 micron JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3x Earth's insolation) super-Earth GJ 486b (1.3 R$_{\oplus}$ and 3.0 M$_{\oplus}$). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2 - 3.3 $\sigma$, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2$\sigma$) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits ($\chi^2_\nu$ = 1.0) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere.
Comment: 18 pages, 7 figures, 5 tables. Accepted in ApJ Letters. Co-First Authors
Databáze: arXiv
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