Word: planetful
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...also a beginning of sorts. Faced with the existence of these planets, astronomers must now revise their theories to fit the new facts. To begin with, theorists have to scramble to explain how the 51 Pegasi planet could have formed and survived intact so close to its parent star. The planet around 70 Virginis is also problematic: its orbit is egg-shaped rather than circular, which suggests to some astronomers that it formed more like a star than like a planet. Indeed, many experts think it is technically a brown dwarf--a star that never got big enough to ignite...
What the data may be saying is simply that the dividing line between stars and planets may be less distinct than astronomers had believed. "Everything found so far poses challenging questions for planetary formation theory," says astronomer Robert Stefanik, of the Harvard-Smithsonian Center for Astrophysics. That was underscored last week when, after weeks of government shutdown, results were released from a NASA experiment much closer to home. The probe's plunge from the Galileo spacecraft into Jupiter's atmosphere showed that the planet has higher winds, less lightning, less water, helium and neon, and--at the point of impact...
More surprises are almost certain to follow if astronomers find more and more planets circling other stars. But while finding new planets of any sort is terrifically exciting, says Alan Boss, an astronomer at the Carnegie Institution of Washington, "the Holy Grail is to find an extrasolar planet that is capable of supporting life...
Despite Goldin's caution about assuming the existence of Earthlike planets, few astronomers doubt they are out there. If other solar systems do contain Earthlike worlds, says NASA exobiologist Michael Meyer, at least some should fall into the "habitable zone"--the region, governed by a planet's distance from its star, where water is liquid rather than solid or gaseous. "The good news," he says, "is that if our solar system is typical, there's a 50% chance that a planet will be in the right zone...
Whether life would inevitably arise from those building blocks is still an open question. With only one example, it is impossible to say whether life on Earth was a fluke or a foregone conclusion. But most biologists cautiously lean toward the latter. Life on this planet emerged surprisingly quickly--as early as a few hundred million years after Earth formed. At the time, the planet was intensely volcanic, with the occasional leftover asteroid screaming in every few million years--yet primitive life forms persisted and flourished...