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Title: Toward the minimum inner edge distance of the habitable zone

We explore the minimum distance from a host star where an exoplanet could potentially be habitable in order not to discard close-in rocky exoplanets for follow-up observations. We find that the inner edge of the Habitable Zone for hot desert worlds can be as close as 0.38 AU around a solar-like star, if the greenhouse effect is reduced (∼1% relative humidity) and the surface albedo is increased. We consider a wide range of atmospheric and planetary parameters such as the mixing ratios of greenhouse gases (water vapor and CO{sub 2}), surface albedo, pressure, and gravity. Intermediate surface pressure (∼1-10 bars) is necessary to limit water loss and to simultaneously sustain an active water cycle. We additionally find that the water loss timescale is influenced by the atmospheric CO{sub 2} level, because it indirectly influences the stratospheric water mixing ratio. If the CO{sub 2} mixing ratio of dry planets at the inner edge is smaller than 10{sup –4}, the water loss timescale is ∼1 billion years, which is considered here too short for life to evolve. We also show that the expected transmission spectra of hot desert worlds are similar to an Earth-like planet. Therefore, an instrument designed to identify biosignaturemore » gases in an Earth-like atmosphere can also identify similarly abundant gases in the atmospheres of dry planets. Our inner edge limit is closer to the host star than previous estimates. As a consequence, the occurrence rate of potentially habitable planets is larger than previously thought.« less
Authors:
; ; ;  [1]
  1. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
Publication Date:
OSTI Identifier:
22341951
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 778; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATMOSPHERES; CARBON DIOXIDE; EARTH PLANET; GLOBAL ASPECTS; GRAVITATION; GREENHOUSE GASES; LOSSES; MIXING RATIO; SPECTRA; STARS; TRANSMISSION; WATER; WATER VAPOR