"The timing for this system to be building an Earth is very good," said study team member Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory in Baltimore, Md.
If the star system were too young, the planet-forming disk would be full of gas, and it would be making gas-giant planets like Jupiter instead. If it was too old, Spitzer would have spotted rocky planets that had long ago formed.
The star system also has the right mix of dusty materials in its disk to form an Earth-like planet, Lisse said.
Using Spitzer's infrared spectrometer instrument, the team determined that the material around HD 113766 is more processed than the snowball-like stuff that makes up infant solar systems and comets, which are considered cosmic "refrigerators" because they contain pristine ingredients from the solar system's formative period. But it is also not as processed as the stuff found in mature planets and asteroids.
"The material mix in this belt is most reminiscent of the stuff found in lava flows on Earth," Lisse said. "I thought of Mauna Kea [in Hawaii] material when I first saw the dust composition in this system – it contains raw rock and it's abundant in iron sulfides, which are similar to fool's gold."