These are perhaps the most exciting of times for SETIphiles. After decades of speculation and theorizing, it appears we finally have definitive proof that planets do indeed orbit other Sun-like stars! The implications for SETI are little short of mind-boggling.
Just a few decades ago, the scientific community held planetary systems to be rare, and in fact many authorities felt ours might be unique. Within a single generation that belief shifted, through acknowledgment that other planetary systems might form under ideal conditions, to a perception that they might be commonplace, to the currently accepted notion that planets may be a necessary mechanism whereby certain classes of rotating stars dissipate some of their angular momentum.
New tools such as the IRAS satellite have allowed us to break free of older beliefs. The disk of proto-planetary dust detected around Beta Pictoris in the 'seventies was our first direct evidence of planetary evolution. Earlier, a strange periodicity in the proper motion of Barnard's Star had delighted planet hunters; attempts to Fourier analyze it into planets proved inconclusive. In the autumn of 1991, Alexander Wolszczan conducted a set of observations at Arecibo which led to the discovery of planets orbiting a pulsar. Other suspected planets around pulsars have subsequently been detected by the NRAO Very Large Array. But it is unlikely that planets bathed in a pulsar's radiation are capable of supporting life. For potentially habitable worlds, we need to examine stars which more or less resemble our Sun.
And now we have our first solid evidence that such worlds exist. On October 6th, 1995, using the Doppler measurement instruments CORAVEL and ELODIE, astronomers Michel Mayor and Dieder Queloz of the Geneva Observatory detected what appeared to be a planet orbiting the star 51 Pegasus. This G2 subgiant is a Solar twin, with nearly identical surface temperature, mass and radius. It is somewhat older than our nearest star (8 Billion years, versus 5 Billion for the Sun), and perhaps 50% richer in iron content. It is visible to the naked eye in the Northern sky just outside the Great Square of Pegasus, and is a mere 42 Light-Years from Earth.
The Internet was immediately abuzz with the news. Debate and speculation were the order of the day. And then, less than two weeks later, independent confirmation came from the Lick Observatory near San Jose CA, where Geoff Marcy and Paul Butler duplicated the Swiss team's measurements almost exactly. There now remains little doubt that a massive planet orbits very close to at least one Sun-like star. We've long suspected that other solar-type stars would harbor planets, but this is the first observation to uphold our theories.
What does the 51 Pegasus discovery imply for SETI? Is the detected planet inhabited? Very likely, not. It has been compared to an iron-nickel bowling ball about half the mass of Jupiter. With a surface temperature of about 1000 degrees C, this doesn't appear to be a particularly good place for ET to call home. On the other hand, it's possible that this is just one of a whole family of planets in 51 Peg's solar system, some of which might be inhabited. From that far out, alien astronomers viewing our Sun might be able to detect only Jupiter. They could merely speculate that it might be part of a retinue of planets, at least one of which harbors intelligent life.
In email exchanges with Seth Shostak at the SETI Institute in California, I have been assured that 51 Peg is on the Project Phoenix target list, and will be monitored across the microwave window, just as soon as the required receivers can be affixed to an appropriate northern-hemisphere antenna. This is altogether appropriate. Yet I am advising SETI League members against training their radiotelescopes on 51 Peg. Why? In answering, I would remind you of the nature of the late NASA SETI program.
Before its funding was terminated by Congress, NASA was conducting a two-pronged radio search of the cosmos. A targeted search of nearby F, G, and K class stars fixed large radiotelescopes on the most likely life sites for long periods of time. This work has been continued by the SETI Institute, under the Project Phoenix banner. An all-sky survey was begun at NASA JPL as a parallel effort. Sky surveys make no a priori assumptions as to the most likely candidates for life, opting instead to systematically scan the entire sky for signals of possible intelligent origin. It is this component of NASA SETI which The SETI League hopes to perpetuate, through our Project Argus.
So which is better, sky survey or targeted search? The two approaches are complimentary. To abandon either would reduce our chances of ultimate success. And that's why we have to view the very good news from 51 Pegasus cautiously. If all 5,000 or so Project Argus participants elect to train their dishes on Pegasus, we might very well miss the next great Wow! signal, coming from some completely different direction. Although the temptation to look at the "hot" spots in the sky is great, we must trust our Project Phoenix colleagues to do their targeted search. They're off to a great start, and we wish them much success. Meanwhile, we are best equipped to contribute by diversifying, not concentrating, our efforts. Ironically, it is by our not becoming too narrowly focused that the promise of Pegasus can best be realized.
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this page last updated 4 January 2003
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