Nov 18 2008
“The prime exploratory challenge of the next fifty years is…surely to seek firm evidence for, or against, the existence of extraterrestrial intelligence,” according to Martin Rees, professor of cosmology and astrophysics at Cambridge University and Astronomer Royal; (see The Next Fifty Years, John Brockman, Ed., 2002).
Finding extraterrestrial intelligence (ETI) would be a compelling long-term goal for humanity in the spirit of Bob Scaringe, who recently suggested interstellar travel (IT) to nearby stars as a way of ensuring human survival as well as motivating a multicentury, global space program. Indeed, the dynamic ETI/IT duo could stimulate a grandiose, long-term program which might even be launched during the next Maslow Window when ebullient extraterrestrial passions are likely to be high.
As of November 14, 2008 The Extrasolar Planets Encyclopedia lists 326 planets — mostly “hot Jupiters” — that have been discovered orbiting other stars. Current optimistic estimates are that the fraction of stars with planetary systems is between 30% and 50%, implying that there could be 50+ billion planetary systems in our Galaxy.
On Earth, humans appeared only about 200,000 years ago suggesting that billions of years might be required for ETI to appear on another planet. Because the Sun’s H-burning Main Sequence (MS) lifetime is 10 billion years, the ratio of humans’ emergence time to the Sun’s MS lifetime is about 0.5. Brandon Carter has suggested that this ratio for ETI will probably be close to 1 (did humans appear “early”?), and that ETI is unlikely in very young planetary systems.
In a provocative article in Journal of the British Interplanetary Society (February, 2008), scientist/author Martin Beech suggests that advanced civilizations near Sun-like stars would eventually engage in planetary engineering of any Mars- or Venus-like planets (e.g., Fogg, 1995) or even Dyson Spheres that could capture most of their star’s energy for use in lofty planetary-scale projects that might be detectable from Earth.
Using age estimates for 123 exoplanet-supporting stars (as of 2005), Beech plots the number of exoplanets vs. the ratio of star age to MS lifetime (a function of star mass); age ratios vary from 0 to 1.5 and the number of exoplanets for each age ratio varies from 1 to 18. Beech suggests that terraforming and Dyson sphere construction might begin as early as 0.4, interstellar migration could flourish from 0.9 to 1.1, and “sterilization” would engulf any planetary system from 1.1 onward as the star becomes a planet-killing red giant.
Beech lists 6 stars of particular interest known to be within 1% of their MS lifetime (i.e., age ratio very near 1). Although no Earth-like planets have been detected in any of these 6 ETI-optimal systems, 3 theoretically allow stable planetary orbits within their habitable zones; they are HD4308, HD190360, and 70 Virginis.
If habitable planets are discovered near these or similar stars, ebullient Earth-bound astronomers contemplating interstellar voyages will check their spectra, to see if “the lights are on” just in case any ETI’s are home.