Privileged Planet: hard to fnd one like us (Introduction)

by David Turell , Monday, June 01, 2015, 04:14 (3465 days ago) @ David Turell

New simulations show how tough it is:-http://planetquest.jpl.nasa.gov/news/192-"For planets to be habitable, they must orbit stars within the 'habitable zone' where it is not too hot or too cold. In addition, recent studies on habitability of planets suggest that the water-land ratio must be similar to the Earth. That is, the water mass fraction should not be far from that of the Earth's (~0.01wt%): planets with too much water (> 1 wt%)-"ocean planets"-lead to an unstable climate and lack of nutrient supply; and water-poor planets like Venus -"dune planets"-become too arid for inhabiting.-***-"Although the detailed numbers in the statistics are not important, Ida and Tian highlight the contrast in the fraction of planets in the habitable zones having Earth-like water content between Sun-like stars and lower-mass stars is significant. At the same time, they caveat that further studies are needed to determine how efficiently water is retained in the mantle, as well as the evolution of its release to the surface."