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From: Icarus Volume 37, Issue 1, January 1979, Pages 351-357 by way of ScienceDirect.com

Habitable zones about main sequence stars

Michael H. Hart1

Systems and Applied Sciences Corporation, 6811 Kenilworth Avenue, Suite 606, Riverdale, Maryland 20840, USA

Received 16 November 1977;
revised 10 July 1978.
Available online 26 October 2002.


Calculations show that a main sequence star which is less massive than the Sun has a continuously habitable zone about it which is not only closer in than the corresponding zone about the Sun, but is also relatively narrower. Let L(t) represent the luminosity after t billion years of a main sequence star of mass M, and let rinner and router represent the boundaries of the continuously habitable zone about such a star—that is, the zone in which an Earthlike planet will undergo neither a runaway greenhouse effect in the early stages of its history nor runaway glaciation after it develops an oxidizing atmosphere. Then our computer results indicate that router/rinner is roughly proportional to [L(3.5)/L(1.0)]1/2. This ratio is smaller for stars less massive than the Sun (because they evolve more slowly), and the width of the continuously habitable zone about a main sequence star is therefore a strong function of the initial stellar mass. Our calculations show that rinner = router for M~0.83M{circle symbol} (i.e., K1 stars), and it therefore appears that there is no continuously habitable zone about most K stars, nor any about M stars.


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