Images from NASA's Kepler mission have found yet another set of Earth-sized planets, but these are something special: The set of five orbit a Sun-like star, and the system may be the oldest of its kind in our galaxy. Researchers reported on the star and its planetary system Tuesday in the Astrophysical Journal.
Named Kepler-444, the star is about 11.2 billion years old. That's 2 1/2 times older than Earth, and well toward the earliest days of the universe.
By looking at the way the star's brightness flickers in and out over time (as planets pass in front of it), astronomers were able to infer how many planets orbit it and what size they are.
"We now know that Earth-sized planets have formed throughout most of the Universe's 13.8 billion year history, which could provide scope for the existence of ancient life in the Galaxy," lead researcher Tiago Campante of the University of Birmingham's School of Physics and Astronomy said in a statement.
"By the time the Earth formed, the planets in this system were already older than our planet is today. This discovery may now help to pinpoint the beginning of what we might call the "era of planet formation," he added.
In the search for life, Earth-sized planets seem like a safe bet. But because they may have formed through processes similar to the ones that formed our home planet, scientists have a lot to learn from them -- even if they're lifeless.