A Cosmos of Bountiful Variation
Two bizarre solar systems whose discoveries were announced last week have inspired a broad range of reactions among astronomers, whose ideas of what planets are and how they work have once again been upended.
Geoffrey W. Marcy, the UC Berkeley scientist who led the California-based discovery team, called the solar systems “frighteningly” different from our own. He pointed out that in the first system, two planets orbit Gliese 876, a red dwarf star 15 light-years away, at dramatically different speeds, with one planet circling twice for every circuit of its companion. However, one of Marcy’s colleagues on the discovery team, Jack Lissauer of NASA’s Ames Research Center in Moffett Field, Calif., found in the same system a reassuring harmony. The tugs and pulls that the two planets give each other may seem bizarre, Lissauer said, but they are balanced in a way that “probably keeps the system stable.” The find, he said, might represent the “best yet found” example of a life-friendly solar system.
The second system--123 light-years away in the constellation Serpens and centered around the star HD 168443--inspired the most vexation because it defies familiar astronomical categories. It contains an object that behaves just like a planet--orbiting a star right next to another detectable planet--but has a mass at least 17 times greater than Jupiter’s, far more than current theories of planetary formation allow.
Astronomers, like all of us, are taken aback by the drastically unfamiliar. But one can’t help thinking that perhaps they have made premature generalizations about what stars and planets “should” look like. The more science learns, the more it seems that the cosmos has installed few limits. In one system found last October, for instance, 18 globes of gas drift freely with no central star to hold them in orbit.
As Alan Boss of the Carnegie Institution in Washington put it, “nature just seems to fill every niche possible with an endless menagerie of planets.” And there’s nothing frightening about that. The rest of the universe is, like Earth, full of innovation.
