Planets by the Hundreds

False-colored infrared picture of the first ever
directly imaged exoplanet (fainter) and its parent star
(a brown dwarf—brighter). Credit: European Southern Observatory.

Exo-planet: it sounds like something the starship Enterprise should be visiting-- and though they have been taken for granted in science fiction for a long time, prior to about fifteen years ago the existence of exoplanet-- short for extra-solar planets, or planets orbiting stars other than our Sun-- was only theoretical.

Today, not only are these far-flung worlds a known fact, they’re being turned out in large numbers by astronomers. In 2006, the same year the number of planets in our Solar System went from 9 to 8, the count of planets orbiting stars other than our Sun exceeded 200, and is climbing at a rate of about one per month.

This is exciting stuff, whether you’re mesmerized by the potential of finding life beyond the Earth or simply intrigued by the possibilities of what may be out there in space, given the sheer number of exoplanets in the galaxy implied by observation-- quite probably in the trillions.

The means by which astronomers detect these distant worlds have been mostly through indirect observation-- observation of the effects a planet has on its parent star, whether by the slight "wobble" in a star or the subtle eclipsing of its light caused by the orbiting planet.

Recently there has been a landmark event in exoplanet research: the first ever direct image of an exoplanet was released to the world. Through observations of infrared light with the European Southern Observatory's Very Large Telescope in Chile, this exoplanet was captured in an image along with its parent, a brown dwarf star.

Most of the exoplanets detected to date are large, gas giant worlds like Jupiter and Saturn. Larger planets produce a greater wobble in the position of their star, and can block out more its light when they cross in front of it. This makes them easier to detect than Earth-sized worlds. Many of the exoplanets discovered tend to orbit relatively close to their parent stars, too; the closer ones orbit their stars more frequently, and so the cycles of their influences play out in shorter periods of time, making them easier to observe and confirm.

In October, 2008, NASA will launch a new spacecraft to hunt for exoplanets: Kepler. Kepler will hunt for Earth-sized planets that orbit their parent stars at greater distance, within what’s called the "habitable zone," the range of distances from a star where conditions are suitable for the formation of life-- at least, life as we know it here on Earth.

While exoplanet research is going on all over the world, the Bay Area is home to more than one exoplanet hunting group. Not only do observers at Chabot Space & Science Center make regular confirming observations of exoplanets, the research team with the greatest number of exoplanet discoveries is led by Dr. Geoffrey Marcy of the University of California, Berkeley, and Dr. Paul Butler of the Carnegie Institute of Washington.

So, the next time you look up at the night sky and view the stars, you can tell yourself that there may be at least one or more planets in orbit around many of them. It’s no longer a thing of science fiction alone...

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.