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Multiple Habitable Phases on Outer Exosolar WorldsAs stars evolve to higher luminosities during first ascension of the giant branch, previously frozen terrestrial worlds may thaw and host liquid water on their surfaces. Eventually these outer worlds again become uninhabitable due to receiving too much incident light and their water inventory evaporating. Solar-mass stars experience a sudden decrease in luminosity entering the horizontal branch, which could result in a secondary habitable phase for their outer worlds. The outer worlds' time with habitable surface climates is key in evaluating the possibility of extraterrestrial life arising. The times inside the habitable zone (TIHZ) are calculated for outer worlds orbiting between 5 and 45 au around a Sun-like star. By comparing the TIHZ to time estimates for life to arise on Earth, we evaluate whether such outer worlds are promising candidates in the search for extraterrestrial life. We use two different solar evolution models (PARSEC and Dartmouth) and both optimistic and conservative habitable zone (HZ) definitions. Multiple habitable phases are found for each outer world. Outer worlds with orbits as large as Saturn are found to have a secondary habitable phase which exceeds the first in duration. Generally, the time inside the HZ is found to decrease almost monotonically with orbiting distance. Water loss is calculated after the first habitable phase to determine whether a secondary habitable phase is possible. For all orbiting distances the water loss is insufficient to deplete a water inventory equivalent to that of many moons in the outer solar system.
Document ID
20240002444
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Viktor Sparrman ORCID
(Uppsala University Uppsala, Sweden)
Sara Bladh ORCID
(Uppsala University Uppsala, Sweden)
M. J. Way ORCID
(Goddard Institute for Space Studies New York, United States)
Date Acquired
February 26, 2024
Publication Date
February 8, 2024
Publication Information
Publication: Astrophysical Journal
Publisher: American Astronomical Society
Volume: 962
Issue: 1
Issue Publication Date: February 10, 2024
ISSN: 0004-637X
e-ISSN: 1538-4357
Subject Category
Lunar and Planetary Science and Exploration
Funding Number(s)
WBS: 811073.02.52.01.08.26
WBS: 811073.02.55.01.20
WBS: 281945.02.03.11.56
CONTRACT_GRANT: SRC 2021-04510
Distribution Limits
Public
Copyright
Portions of document may include copyright protected material.
Technical Review
External Peer Committee
Keywords
Astrobiology
Exoplanet evolution
Exoplanets
Habitable planets
Natural satellites (Extrasolar)
Solar evolution
Evolved stars
Horizontal branch stars
Habitable zone
Red giant branch
Solar analogs
Stellar evolution
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