“Men, like planets, have both a visible and an invisible history,” wrote George Eliot. Actually, most planets have only an invisible history—we know them only through their indirect influences on the things we do see. Astronomers have yet to make a direct image of a true planet outside our solar system. Michael Liu of the University of Hawaii and his colleagues are now starting the most ambitious search so far, combining a new coronagraph (which masks out the host star), a high-sensitivity adaptive optics system (which de-twinkles the light), and a spectral subtraction technique that wrings out the remaining stellar glare by focusing on emission from methane (which sunlike stars, being too hot, do not contain). A Jupiter-size world in a Jupiterlike orbit around a young star would show up. Not only would direct images reveal bodies that indirect ones do not, they would show much more detail, including atmospheric composition and perhaps even potential signs of life.
This article was originally published with the title "Direct Gaze" in Scientific American 295, 3, 36 (September 2006)