A Blip on a Telescope in a Colorado Parking Lot Bolstered a Space Mission That Has Found Thousands of Planets … and Counting

An illustration of all 726 solar systems depicting planets confirmed as of October 30, 2018, the end of Kepler s life span. The colors represent each planet s temperature, ranging from chilly dark blue to fiery red. The mission yielded so much data that scientists are still announcing new planets years later. Data Visualization by Ethan Kruse On September 9, 1999, a 25-year-old Harvard graduate student, David Charbonneau, made one of the closing century’s most consequential astronomical discoveries, using a four-inch telescope set up inside a plywood shed in a Colorado parking lot. Charbonneau and his adviser, Tim Brown, who had built the telescope, had been measuring the light from a sunlike star with the undramatic designation HD 209458. They hoped to use a technique called photometry—measuring a star’s light—to confirm speculations that HD 209458 had an orbiting planet. At the time, NASA was deciding whether to fund the Kepler mission, a space telescope that would use the same technique. Kepler was a long shot, because photometry had never before detected a planet orbiting a star outside our solar system. Brown and Charbonneau were about to change a long shot into a sure bet.

In 1999, there were very few confirmed exoplanets, or planets outside our own solar system, and these were gas giants on the order of Jupiter, not smaller, rocky planets like Earth. They had been confirmed using a method known as Doppler spectroscopy, which registered shifts in the color spectrum over time as the star was tugged to and fro by orbiting planets. Doppler was useful for finding Jupiter-size planets that were close to their stars, but it couldn’t always deliver clear data on smaller planets that were farther from their stars. Astronomers using Doppler spectroscopy had noticed something unusual happening around HD 209458, about 150 light-years from Earth, but the “wobbles” in the color spectrum could have had another cause, such as the star contracting and expanding.

In theory, the photometry method that Charbonneau and Brown used would be able to show more decisively whether a planet was orbiting a far-off sun. Many photometric telescopes couldn’t register changes in brightness that were smaller than a few percent. But Brown designed his telescope to continuously monitor a change in a star’s brightness as small as 1 percent—the dip a Jupiter-size planet would cause as it passed in front of its star.