October 2, 2013 - Robert Frostâ€™s classic 1923 poemÂ â€ťNothing Golden Can Stayâ€ť isÂ certainly true for planets that are in the habitable
zone â€” or shall we say the golden zone â€” around their parent stars.
A planetâ€™s lease on life runs out when the evolving star grows too hot for the world hold onto water for sustaining life as we know it. With increasing stellar luminosity, the habitable zone sweeps outward beyond the planetâ€™s orbital radius, leaving paradise worlds to bake to death as surviving extremophliles burrow underground.
Whatâ€™s sobering is that Earth
has already spent 70 percent of its habitable years inside the sunâ€™s golden zone. Â And it took that long for intelligent life to appear on the surface.
Weâ€™ve got about 1.7 billion years left, according to a paper published by Andrew Rushby and co-authors in Astrobiology Magazine. When the sun reaches 118 percent the brightness of what it is today our oceans will evaporate away and Earth
will be desiccated, resembling the terrain on Saturnâ€™s moon Titan.
The scientists say the best place buy real estate for long-term habitability is around a red dwarf star. A planet can remain cozy for advanced life for a stretch of time that is five times greater than for Earth. All other thing being equal, this suggests that SETI searches should target red dwarfs to see if they are home to advanced civilizations that do not have to worry about the clock running out.
There have been numerous news announcements, mostly from NASAâ€™s Kepler planet hunting observatory, about the discovery of so-called â€śEarth-likeâ€ť worlds nestled inside a starâ€™s habitable zone.
"We thought we would have to search vast distances to find an Earth-like planet. Now we realize another Earth is probably in our own backyard, waiting to be spotted," said Courtney Dressing of the Harvard-Smithsonian Center for Astrophysics (CfA). Six percent of red-dwarf stars have habitable, Earth-sized planets, astronomers at the...