Water loss from terrestrial planets orbiting ultracool dwarfs: implications for the planets of TRAPPIST-1

By É. Bolmont, F. Selsis, J. Owen, I. Ribas, S. Raymond, J. Leconte, M. Gillon. 2016

188 citations recorded by the source corpus.

Ultracool dwarfs (UCD) encompass the population of extremely low mass stars (later than M6-type) and brown dwarfs. Because UCDs cool monotonically, their habitable zone (HZ) sweeps inward in time. Assuming they possess water, planets found in the HZ of UCDs have experienced a runaway greenhouse phase too hot for liquid water prior to entering the HZ. It has been proposed that such planets are desiccated by this hot early phase and enter the HZ as dry, inhospitable worlds. Here we model the water loss during this pre-HZ hot phase taking into account recent upper limits on the XUV emission of UCDs and using 1D radiation-hydrodynamic simulations. We address the whole range of UCDs but also focus on the planets b, c and d recently found around the 0:08 M dwarf TRAPPIST-1. Despite assumptions maximizing the FUV-photolysis of water and the XUV-driven escape of hydrogen, we find that planets can retain significant amounts of water in the HZ of UCDs, with a sweet spot in the 0:04 ‐ 0:06 M range. With our assumptions, TRAPPIST-1b and c can lose as much as 4 Earth Ocean but planet d ‐ which may be inside the HZ depending on its actual period ‐ may have kept enough water to remain habitable depending on its initial content. TRAPPIST-1 planets are key targets for atmospheric characterization and could provide strong constraints on the water erosion around UCDs.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/7cba7548c160b4f1861be1fec151638106f625a8

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Citations in the corpus

• Strange messenger: A new history of hydrogen on Earth, as told by Xenon (2018, background): “ given mass out of Earth’s potential well and into space (Watson et al., 1981). Details are lumped together in an eciency factor that is often taken to lie between 0.1 and 0.6 (Lammer et al., 2013; Bolmont et al., 2017). In one version of the energy limit, all XUV photons that can be directly absorb”
• Habitable Moist Atmospheres on Terrestrial Planets near the Inner Edge of the Habitable Zone around M Dwarfs (2017, background): “…Wordsworth et al. 2010; Abe et al. 2011; Haqq-Misra & Kopparapu 2015; Barnes et al. 2016; Meadows et al. 2016; Ribas et al. 2016; Turbet et al. 2016; Bolmont et al. 2017), and studies such as these provide a valuable contribution in understanding, and eventually interpreting, any biosignatures.”
• The Transit Light Source Effect: False Spectral Features and Incorrect Densities for M-dwarf Transiting Planets (2017, background): “…et al. 2017) and strong XUV radiation from the host star (Wheatley et al. 2017), however, can lead to significant water loss for these planets (Bolmont et al. 2017), and 3D climate modeling suggests TRAPPIST-1e provides the best opportunity for present-day surface water and an Earth-like…”
• Habitability from Tidally Induced Tectonics (2018, background): “As luminosity decreases, the remaining water in the atmosphere will condense out (Bolmont et al. 2017; Schaefer et al. 2016), or perhaps any water stored in the mantle can outgas to the surface.”
• Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST (2017, background): “Bolmont et al. (2017) studied the potential water loss driven by FUV photolysis of water and subsequent XUV-driven escape of hydrogen from the TRAPPIST-1 system, and they found that the inner two planets have likely lost a significant amount of water while the outer planets likely retain more of…”
• Modeling climate diversity, tidal dynamics and the fate of volatiles on TRAPPIST-1 planets (2017, background): “We remind that a potentially thick O2 atmosphere could have built up abiotically during the early runaway phase (Luger & Barnes 2015; Bolmont et al. 2017) while TRAPPIST-1 was a pre-main-sequence star, playing potentially a strong role here on the haze formation.”
• The nature of the TRAPPIST-1 exoplanets. (2018, background): “Within these assumptions and considering the expected intense atmospheric escape around TRAPPIST-1 (Bolmont et al. 2017), the lifetime of such atmospheres would be very limited, making this scenario rather unlikely.”
• The Cosmic Shoreline: The Evidence that Escape Determines which Planets Have Atmospheres, and what this May Mean for Proxima Centauri B (2017, background): “scape can be expressed as M_ el = ˇR3L xuv(t) 4ˇa2GM (28) where is an eciency factor that is usually taken to be 0:1 <<0:6 (e.g., Lammer et al. 2013; Owen and Wu 2013; Koskinen et al. 2014; Bolmont et al. 2017). The mass loss eciency is less than the heating eciency (fraction of incident XUV e”