Researchers collected infrared light from both the planets and their nearby stars. When an orbiting planet passed behind its star, new measurements revealed the light originating from the star alone. The difference is the exact amount of infrared light coming from each planet.
"In visible light, the glare of the star completely overwhelms the glimmer of light reflected by the planet," Charbonneau explained. "In infrared, the star-planet contrast is more favorable, because the planet emits its own light."
The Web site of the science journal Nature published the Deming paper yesterday. The Charbonneau paper will appear in an upcoming issue of the Astrophysical Journal.
Additional observations will map each planet's infrared light spectrum, which can tell scientists about the composition of the two distant worlds.
Yesterday's announcement also highlighted the mystery surrounding HD 209458b's unusual, puffy size.
"So far there is no particularly promising explanation of why it is so large," Deming said. "In this case we're left with a mystery to be solved."
Many more such quandaries will surely arise now that planets can be detected with infrared light.
"Spitzer was not designed to find planets, but it has led us to this first discovery and whets our appetite for what's coming in the next ten years," said Alan Boss, a staff research astronomer with the Carnegie Institution in Washington, D.C.
"Hot Jupiters are interesting, but in the end we really want to find warm Earths as well," he said.
Old, Cold, and Dirty
All celestial objects with temperatures above absolute zero (273° Celsius/460° Fahrenheit) emit infrared radiation, or heat. With an infrared orbiting telescope such as Spitzer, astronomers can detect distant or faint sources of radiation that would otherwise be distorted by Earth's atmosphere.
Spitzer is the last of NASA's four orbiting "Great Observatories." The group includes the Hubble Space Telescope, the Compton Gamma-Ray Observatory, and the Chandra X-Ray.
Researchers use this multifaceted tool kit to glimpse the origins of galaxies, stars, and planets.
Spitzer team scientists like to describe their mission as a search for "the old" (the earliest stars and galaxies), "the cold" (brown dwarfs, possibly stars that failed to ignite, and circumstellar discs, broad rings of material orbiting a star) and "the dirty" (dust-obscured processes such as star and planetary formation).
The Spitzer telescope is also a key component of the NASA Origins Program, which seeks to answer the fundamental questions: Where did we come from, and are we alone?
The planetary observations are the second major Spitzer announcement in less than a month.
On March 1, NASA revealed that the telescope had discovered a hidden group of exceptionally bright galaxies some 11 billion light-years away in deep space.
Though the galaxies were as bright as 10 trillion suns, their great distance and a cloak of cosmic dust had hidden them from all but Spitzer's finely tuned infrared apparatus.
The telescope recently recorded its ten-thousandth unique observation. The instrument has focused on everything from stars and brown dwarfs (radiation-emitting celestial objects that are smaller and dimmer than stars) to interstellar clouds of gas.
Many more observations should follow over the next few years. Spitzer is expected to enjoy a lifetime of two and a half to five years or more, while gradually drifting away from Earth's orbit toward deep space.
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