HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES

By R. Kopparapu, R. Ramirez, J. Kasting, Vincent Eymet, T. Robinson, S. Mahadevan, R. Terrien, S. Domagal‐Goldman, V. Meadows, R. Deshpande. 2013

1,045 citations recorded by the source corpus.

Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity (RV) and transit exoplanet surveys and proposed future space missions. Most current estimates of the boundaries of the HZ are based on one-dimensional (1D), cloud-free, climate model calculations by Kasting et al. However, this model used band models that were based on older HITRAN and HITEMP line-by-line databases. The inner edge of the HZ in the Kasting et al. model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO2 atmosphere. A conservative estimate for the width of the HZ from this model in our solar system is 0.95–1.67 AU. Here an updated 1D radiative–convective, cloud-free climate model is used to obtain new estimates for HZ widths around F, G, K, and M stars. New H2O and CO2 absorption coefficients, derived from the HITRAN 2008 and HITEMP 2010 line-by-line databases, are important improvements to the climate model. According to the new model, the water-loss (inner HZ) and maximum greenhouse (outer HZ) limits for our solar system are at 0.99 and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water-loss limits for stars with Teff ≲ 5000 K, which has implications for ongoing planet searches around K and M stars. To assess the potential habitability of extrasolar terrestrial planets, we propose using stellar flux incident on a planet rather than equilibrium temperature. This removes the dependence on planetary (Bond) albedo, which varies depending on the host star's spectral type. We suggest that conservative estimates of the HZ (water-loss and maximum greenhouse limits) should be used for current RV surveys and Kepler mission to obtain a lower limit on η⊕, so that future flagship missions like TPF-C and Darwin are not undersized. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/131ff694548df1138f3ed778900e7bccbe761ea3

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Citations in the corpus

• The Habitability of Planets Orbiting M-dwarf Stars (2016, background): “…of Rayleigh scattering then dominate over the greenhouse effect of increased CO2, and temperatures above the freezing point of water can no longer be maintained by increasing CO2 (Kasting et al., 1993; Underwood et al., 2003; Pierrehumbert, 2010; Kane & Gelino, 2012; Kopparapu et al., 2013a,b).”
• THE INNER EDGE OF THE HABITABLE ZONE FOR SYNCHRONOUSLY ROTATING PLANETS AROUND LOW-MASS STARS USING GENERAL CIRCULATION MODELS (2016, methodology): “D models (Kopparapu et al. 2013, 2014).”
• Frequent Flaring in the TRAPPIST-1 System—Unsuited for Life? (2017, background): “We can also do a rudimentary estimation how such eruption changes temporarily the limits of the habitable zone based on the model of Kopparapu et al. (2013).”
• AN ANCIENT EXTRASOLAR SYSTEM WITH FIVE SUB-EARTH-SIZE PLANETS (2015, background): “These orbits are well interior to the inner edge of the system’s habitable zone, which lies 0.47 AU from the parent star if we consider the rather optimistic ‘Recent Venus’ limit of Kopparapu et al. (2013).”
• THE OCCURRENCE OF POTENTIALLY HABITABLE PLANETS ORBITING M DWARFS ESTIMATED FROM THE FULL KEPLER DATASET AND AN EMPIRICAL MEASUREMENT OF THE DETECTION SENSITIVITY (2015, methodology): “In the most conservative case, we adopt the maximum greenhouse (Max GH) and moist greenhouse (Moist GH) insolation limits from Kopparapu et al. (2013b).”
• Trumpeting M dwarfs with CONCH-SHELL: a catalogue of nearby cool host-stars for habitable exoplanets and life (2014, methodology): “We calculated the stellar irradiation in terrestrial units using S = L∗(P/365.24 d) −4/3M −2/3 ∗ and we ascertained whether planets orbit in the habitable zone described by the Teff - dependent “runaway” and maximum CO2 greenhouse limits on S proscribed in Kopparapu et al. (2013).”
• How to Characterize Habitable Worlds and Signs of Life (2017, background): “Slowrotating planets could maintain habitability for higher incident fluxes than fast-rotating planets due to increased cloud coverage on the dayside of the planet, making synchronously locked planets at the inner edge of the HZ interesting test cases for this hypothesis (see, e.g., Wolf & Toon 2014”
• Water loss from terrestrial planets orbiting ultracool dwarfs: implications for the planets of TRAPPIST-1 (2016, methodology): “Earth-like planets have been detected in the HZs (defined in Kasting, Whitmire, & Reynolds 1993; Selsis et al. 2007a; Kopparapu et al. 2013) of early type M-dwarfs (e.g., Quintana et al. 2014).”
• Geologic Constraints on Early Mars Climate (2018, background): “Such low insolation puts Early Mars outside the circumstellar habitable zone – at least according to basic forward models of habitable-planet climate (Kasting et al. 1993, Kopparapu et al. 2013).”
• FALSE POSITIVE PROBABILITIES FOR ALL KEPLER OBJECTS OF INTEREST: 1284 NEWLY VALIDATED PLANETS AND 428 LIKELY FALSE POSITIVES (2016, background): “…potentially habitable planets, Table 3 lists the properties of 9 CANDIDATE KOIs newly validated by this work that may fall within the optimistic habitable zones of their host stars (Kopparapu et al. 2013), according to the stellar properties reported by the DR24 table at the NExScI Archive.”
• Is Proxima Centauri b Habitable? A Study of Atmospheric Loss (2017, background): “The Habitable Zone (HZ) is broadly defined as the region around a star where a planet can support liquid water for certain values of the atmospheric pressure (Lammer et al. 2009), and has been extensively investigated (e.g. Kasting et al. 1993; Kasting & Catling 2003; Kopparapu et al. 2013).”
• Prevalence of Earth-size planets orbiting Sun-like stars (2013, background): “Pierrehumbert and Gaidos (18) estimated that the outer edge of the HZ may extend up to 10 AU for planets that are kept warm by efficient greenhouse warming with an H2 atmosphere.”
• A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone (2013, methodology): “Traditionally, analyses of planetary habitability begin with determining if a planet is in the habitable zone (Dole 1964; Hart 1979; Kasting et al. 1993; Selsis et al. 2007; Kopparapu et al. 2013), but many factors are relevant.”
• The nature of the TRAPPIST-1 exoplanets. (2018, background): “Planet b however, is located beyond the runaway greenhouse limit for tidally locked planets (Kopparapu et al. 2016; Turbet et al. 2017) and could potentially reach – with a thick water vapour atmosphere – a surface temperature up to 2000 K (Kopparapu et al. 2013).”
• A REVISED ESTIMATE OF THE OCCURRENCE RATE OF TERRESTRIAL PLANETS IN THE HABITABLE ZONES AROUND KEPLER M-DWARFS (2013, methodology): “Here we use the Kopparapu et al. (2013) HZ limits to derive revised estimates of occurrence rates of potentially habitable planets around low-mass stars.”
• Habitable Moist Atmospheres on Terrestrial Planets near the Inner Edge of the Habitable Zone around M Dwarfs (2017, methodology): “Our own previous work on HZs (Kopparapu et al. 2013, 2014) using a 1D radiative-convective, cloud-free climate model, and updated with new and stronger H O2 absorption coefficients from HITRAN2008 and HITEMP2010 line-by-line (LBL) databases, showed that the inner edge of the HZ can be significantly…”