Symphony of New Planets

One of the fundamental premises of all SETI science is that inhabitable worlds are not rare. This assumption has garnered plenty of indirect support during the last several years as astronomers have finally succeeded in finding planets that orbit ordinary (and nearby) stars.

Of course, most readers will know that these planets are not the type that E.T. would prefer to call home. Many of them are "hot Jupiters" - giant worlds circling very close to their stellar hosts. While no one is certain, they are likely to be similar to the outer planets of our own solar system, boasting thick atmospheres of, for example, methane and ammonia. This environment makes for great cleaning fluid, but might be a difficult venue for life. In addition, the "hot Jupiters" will be a bit toasty for E.T.'s taste: typically 1,000 C.

"Hot Jupiters" - Giant worlds closely circling their stellar hosts

Some of the planets found in the last several years are farther out, but in highly eccentric orbits (somewhat like comets) alternately plunging close to their star, and then diving back out into the more distant regions of their solar systems. These eccentric worlds are also hefty, comparable to Jupiter in mass.

Recent observations have uncovered more of these distant bodies, bringing the total to over 160. The new planets are again the big boys of space, but not all are quite so heavy-duty. Swiss astronomers (including Michael Meyor and Didier Queloz, who first found the planet around 51 Peg) have uncovered two Saturn-sized worlds around the star HD 83443, as well as another planet that's smaller yet: half of Saturn's mass.

The other discoveries are heftier, typically several Jupiters in size. But what's interesting is that Berkeley group of planet hunters, including Debra Fischer, Geoff Marcy and Paul Butler, are finding more worlds that are "far out," celestially speaking. These are planets that don't hug their suns quite so tightly, and are more comparable to the situation in our own solar system, where big planets orbit at large radii. Keep in mind that it is the nature of the techniques used to discover these planets that they are most sensitive to big worlds, close in. So the astronomers will perforce find big worlds, close in!

Jupiter compared to possible other planets
Typically, the planets discovered are several times the size of Jupiter

It's also the case that the Berkeley team is finding that about half of the new planets may be in multiple systems. In other words, solar systems may be common, with planets being born in "litters."

One of the most interesting of the new discoveries, from the SETI perspective, is that of a planet around the K-type star, Epsilon Eridani, a mere 10.5 light-years away. This was found by Bill Cochran and co-workers at Texas' McDonald Observatory. Epsilon Eridani is one of the closest sun-like stars, and discovering a planet there is like finding an alligator in your back yard: it implies that alligators (or in this case, planets) must be very common indeed.

In addition, Epsilon Eridani was one of the two stars looked at by Frank Drake in his pioneering Project Ozma SETI search during the Spring of 1960. In fact, Frank detected a signal when his 85-foot antenna was swung in the direction of Epsilon Eridani, which prompted him to wonder "could success be this easy?" He later determined that the signal was terrestrial interference, but it's intriguing how prescient Drake was in selecting this star system - now known to be a home to planetary worlds.

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