So far, astronomers have discovered some 130 stars outside our solar system that have planets orbiting them. All of these were initially detected using indirect methods, such as analyzing the effect they have on their star's position. Now a team led by Drake Deming at NASA's Goddard Space Flight Center has measured light from the planet known as HD 209458b, which orbits a star 153 light-years away from our planet. David Charbonneau of the Harvard-Smithsonian Center for Astrophysics and his colleagues, meanwhile, observed the light from the planet TrES1, located more than three times as far away near the constellation Lyra.
The two groups used the same technique to measure the light from the far away worlds. "Planets like TrES-1 are tiny and faint compared to their stars, but the one thing they can't hide is their heat," remarks Charbonneau. "We are like detectives. Previous clues told us the planet must be there, so we put on our 'infrared goggles' and suddenly, it popped into view." The researchers used the infrared region because in it, the star is only about 400 times brighter than the planet, whereas the star outshines TrES-1 by about 10,000 times in the visible light spectrum. By observing the changes in light intensity as the planet passed behind its star, the scientists were able to separate out the planet's contribution to the glow.
The researchers determined the TrES-1 reaches about 1,450 degrees Fahrenheit and has a reflectivity of only 31 percent, which means that it absorbs the majority of light that falls on it from its nearby star. HD 209458b, on the other hand, reaches 1,574 degrees Fahrenheit. "Detecting light from these other worlds is very exciting," remarks HD 209458b team member Sara Seager of the Carnegie Institution. "It opens a whole new window on these objects. It's the beginning of our ability to study their temperature, and composition." Papers describing the findings will be published in the April 7 issue of Nature and the June 20 issue of the Astrophysical Journal.