The COROT mission, to be launched in December, promises to move us to the next level of planetary detection. Devoted to studying exoplanet transits, in which a planet crosses the face of its star as seen from Earth, the space telescope will probably detect numerous ‘hot Jupiters.’ But an even more interesting possibility is rocky worlds in close orbit around their stars. And the thinking is that planets only a few times larger than Earth — and perhaps even smaller than that — will be within its reach.
Any star with a transiting planet will provide a telltale drop in light that, depending on the size of the planet and the distance of the star, may be measurable. But COROT (the acronym stands for Convection Rotation and planetary Transits) is most sensitive to rocky worlds in orbits of 50 days or less. If that sounds dismaying in terms of habitability, consider that a planet in such an orbit around a dim red dwarf could be located ideally within the star’s habitable zone. And red dwarfs comprise on the order of 70 percent of the stars in the Milky Way (excluding brown dwarfs).
Also under study is the intriguing field of asteroseismology. As sound waves ripple across a star’s surface, they produce variations in its light that help us understand the internal conditions of the star. Asteroseismology sounds exotic, but it’s already well established in the study of our own Sun. The Solar and Heliospheric Observatory (SOHO) has fine-tuned the method. Now COROT will target at least fifty stars for specific study in its examination of stellar evolution.
Launch is scheduled for the end of the year at the Soyuz-Fregat launcher at Baikonur, Kazakhstan. As we get COROT into space and anticipate the Kepler launch in October of 2008, it’s heartening to consider how far we’ve come. The earliest planetary detections were short period worlds; i.e., planets that completed their orbits in mere days. They’re easier to detect because they produce the strongest data signature, but long-period planets are a much harder catch.
Nonetheless, teams have been observing numerous stars in an attempt to build up enough data to detect such worlds, and the results are beginning to come in. That has opened up the study of multiple planets in systems already known to have one, and it begins to flesh out our picture of how planetary systems diverge. Moving into the era of small, rocky worlds has big implications as we hunt out possible havens for life. The bet here is that red dwarfs are going to prove fertile hunting grounds for planets of the right distance, size and composition. But finding an Earth-sized world around a Sun-like star remains the ultimate prize.