To See the Inevitable Dream: Earthlike Exoplanets
The SETI field, while always seeking to detect and encrypt actual communications from aliens, has been plagued by not yet being able to pinpoint even one suitable extrasolar planet where life could exist. In many ways, this was then an impossible dream because it never had been done, yet. My interest during those early days (a third of a century ago) of finding an Earthlike planet circling another star has, shockingly enough, still eluded the experts. But this dream is no longer impossible, it is now inevitable. Drawing together some of the historical threads previously mentioned, let us now focus on task #1: find Earthlike exoplanets.
Remember, NASA does fund these searches. However, astroscientists mostly use INDIRECT methods to hunt for exoplanets, like astrometry (measure a star’s position in the sky—if there is a planet, then the orbit would be affected), radial velocity (determine variations in the speed at which the star moves from or to our planet, the change surmised to be caused by a planet—this has been the most productive method), pulsar timing (detect anomalies from the precise radio pulses, which must be caused by a planet) and a host of other esoteric techniques. In short, wobbles are measured and programmed for computer matching with a possible planet or more.
The direct means used involve the transit method (when a planet crosses in front of the star, the brightness drops—you need to be really lucky for this one), circumsteller disks (where space dust can more easily be detected, with any features suggesting a planet) and others. Some of these direct techniques could probably also have been utilized by Galileo.
Take one direct technique, planet dimming. Searchers are focusing on M-dwarfs, faint red stars, which make up 70% of all stars. In these solar systems, it is possible to obtain light reduction of up to 1% when a planet passes across the star, as compared to 0.001% dimming if you were viewing from many light years away and Earth blocks the light of our Sun, a G2 star. But life prospects are not exciting for M-dwarf systems. So why? We already know there are planets outside our solar system.
When was the first extrasolar planet truly detected? This remains somewhat controversial, but it was in 1988 that Canadian astronomers Bruce Campbell, G. A. H. Walker and S. Yang, using radial velocity observations, first cautiously claimed success. The first published and confirmed paper appeared in 1992 when Polish astronomer Aleksander Wolszczan and Canadian radio astronomer Dale Frail announced the discovery of planets around a pulsar. In 1995, Swiss astronomers Didier Queloz and Michel Mayor saw a planet orbiting a typical star, using high resolution spectroscopy.
At the end of 2005 there were 150 exoplanets identified (406 as of December 8, 2009). On November 7, 2007, the W.M. Keck Observatory reported on a fifth planet orbiting 55 Cancri, a star about the same size as our Sun, and just 41 light years away. But none of them would qualify to harbor life as we know it, for most of these exoplanets are Jupiter-sized with very short orbit periods. But, of course, that is because the current techniques can only find these, except for those lucky dimming observations.
Absent really useful data because all the planets unwobble-ized, as of 2007, are too large, a planet orbiting the red dwarf star Gliese 581 (artist conceptualization above from National Geographraphic News), could be at a probable surface temperature where liquid water might be possible. Discovered on April 24, 2007 by a Swiss team using a radial velocity technique in La Sill, Chile, the speculation is that this exoplanet is not good enough because Ymir, still officially called Gliese 581 c, has about five times the mass of Earth, an orbital radius only about 7% that of Earth (but the red dwarf is cooler than our Sun) and a period of only 13 days (that is, it takes 13 days to revolve around the star). Gliese 581 is 20.5 light years away and, apparently, has four possible planets. When you look up into the night sky, you can’t help, though, but be impressed with how in the heck astroscientists can glean so much information from a rotating body so far away.
The first earth-like exoplanet approximating the size of our globe (1.7 times larger) is COROT-7B was found early this year. Close to 500 light years away, it was discovered photometrically. The problem is that the temperature is 3600 degrees F facing its star and minus 328 F on the backside. It also has a year shorter than 24 hours. Here is an artist's concept of what the system might look from GEARlog:
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