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Planets, Planets Everywhere
by Dr. H. Paul Shuch, Executive Director

An assumption fundamental to all SETI research is an abundance of habitable extra-solar planets. Since the existence of communicative civilizations seems to require planets upon which they might build their homes, cities and antennas, the whole house of cards constructed out of the Drake Equation collapses if planetary formation is as rare as was once believed. Fortunately, every day seems to bring new evidence that planetary systems around Sun-like stars are commonplace.

Bear in mind that optical detection of planets orbiting distant stars is still beyond our capability. As has been pointed out previously, visually spotting such planets is a little like trying to see a firefly perched on the rim of a searchlight. Because suns saturate our photodetectors, other means of planetary detection must be devised. And they have been.

The first known planetary system other than our own was confirmed as recently as 1994. The next such discovery occurred a year and a half later. And just three months after that, two new solar systems were discovered. The near geometric progression suggests that soon we shall be discovering new solar systems on a daily basis. Then the existence of other worlds will cease to be news, and become an accepted fact of SETI.

Most encouraging for our endeavor is that the three most recent planetary discoveries have all involved G class stars, very much like our own Sun. Although the sample size is still small, it's beginning to appear that planets circling stars such as our own might be commonplace. One of the latest planets appears to have a surface temperature consistent with the possible existence of liquid water. Though not necessarily essential to the development of life, the presence of oceans certainly simplifies the process.

None of this makes SETI success any more of a certainty than it was a few years ago. But it does seem to raise substantially the values which we might assign to the variables at the left of the Drake Equation. The numbers toward the right are just as speculative as they ever were. Still we should be encouraged by the recent surge of planetary discoveries. And we will keep searching. It remains obvious to me that if we do not, N will for all practical purposes continue to equal 1.

N = R* fp ne fl fi fc L

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