Sometimes not seeing is believing. Ask Mike Brown, whose research team has now found several icy, planet-size objects in the far reaches of the solar system, including Sedna and, most recently, Xena, the would-be Pluto killer. Whether the discoveries count as planets is for experts at the International Astronomical Union to decide (a task they keep avoiding). What is clear, thanks to Brown and his colleagues, is that our celestial backyard is much busier and bigger than anyone imagined. Xena is the most distant object yet seen in orbit around the sun, about 10 billion miles away, three times farther from the sun than Pluto.
Just as remarkable, though, is how Brown's team found these objects—and that they found them at all. As Brown tells Discover this month, he was convinced that Pluto-size (and larger) entities exist out there somewhere. He spent years hunting for them but to no avail, mostly because his telescope was too weak and it was pointed in the wrong direction. When a better instrument came along, he boldly tossed out three years of data and started fresh, with better aim, better resolution, and spectacular results.
In the storybook version of astronomy, a solitary observer studies the night sky through a telescope—just an eye, the cosmos, and some lenses in between. The real job requires both more imagination and more advanced tools. These days almost all astronomical discoveries are "seen" only by computerized cameras; Brown saw his on a desktop screen. "I've never really seen any of the things I find," he says. "By 'see' I mean looking through a telescope and having photons actually hitting the eye." That may be a letdown, but scientific "seeing" has rarely been that direct. Galileo's troubles with the Catholic Church were as much technological as theological: What reasonable person would embrace discoveries based on evidence collected through a device (the telescope) that was built by the discoverer and that few other observers could actually see much through? In 1800, several decades after the microscope was invented, the renowned French pathologist Marie-François-Xavier Bichat considered it so unreliable that he banned its use in the laboratory.
To speculate (from the Latin root speculari, "to spy out") is to see beyond the seen, to peer into the dark and discern some substance and pattern. It is an essential tool for astronomers and derives from the understanding that what the unaided human eye can perceive is the least of what's out there. Two years ago, the Bush administration hailed as visionary its plan to send astronauts to the moon and Mars—a plan, it now appears, that may well doom farther-seeing astronomy projects like the Terrestrial Planet Finder and a robotic mission to explore the prospects for life on Jupiter's moon Europa. The vision, though inspiring, presumes that the best way to decipher the cosmos is to see it directly ourselves. Unbelievable.
