Virtually yours

In recent years astronomers have been busy discovering planets around other stars. These have been almost entirely big Jupiterlike planets, for the obvious reason that big planets are easier to detect. What was surprising is that many of these big gassy planets were very much closer to their host star than the giants in our own solar system. It has long been thought that gassy giants can only form in the cooler outer regions of star systems.

In a recent issue of Science (September 8), astronomers Sean Raymond, Avi Mandell and Steinn Sigurdsson help explain these apparently exotic worlds by simulating planet formation on a computer. The illustration here show one such simulation, in which a giant planet forms at a respectable Jupiterlike distance, then in the course of 200 million years migrates (because of dynamic forces in the protoplanetary disk) closer to its star. Other smaller planetoids coalesce into more Earthlike planets, including one with liquid water at an Earthlike distance. Voila! Everyone is happy. (The gray area on the bottom time slice is the so-called "habitable zone" where temperatures are neither too hot nor too cold for life as we know it.)

What I like about all of this is the way astronomers use powerful, high-speed computers to play with planets and stars. Start with the physics, run the simulation, compare the results with what we observe with telescopes. There are even wild-eyed sci-fi buffs who imagine that our own "real" solar system -- including us -- might be a simulation in the super-supercomputers of a super-super race.

I'll settle for the opportunity that computer-savvy astronomers give me to be a spectator at creation.