Ancient star with five Earth-size planets discovered

After analysing over four years of data from NASA's Kepler spacecraft, a team of astronomers has discovered a star that is 11.2 billion years old and has at least five Earth-size planets.

"The findings show that Earth-size planets have formed throughout most of the universe's 13.8-billion-year history, leaving open the possibility for the existence of ancient life in the galaxy," said Tiago Campante, research fellow at the University of Birmingham who led the research project.

The paper describes Kepler-444, a star that is 25 percent smaller than our Sun and is 117 light years from Earth.

The star's five known planets have sizes that fall between Mercury and Venus.

Those planets are so close to their star that they complete their orbits in fewer than 10 days.

At that distance, they are all much hotter than Mercury and are not habitable.

"Kepler-444 is very bright and can be easily seen with binoculars. This is one of the oldest systems in the galaxy," added Steve Kawaler, an Iowa State University professor of physics and astronomy and co-author of the paper.

Kepler-444 came from the first generation of stars.

"This system tells us that planets were forming around stars nearly seven billion years before our own solar system," Kawaler noted.

Planetary systems around stars have been a common feature of our galaxy for a long, long time.

That discovery is going to help astronomers learn even more about the history of the Milky Way.

"From the first rocky exoplanets to the discovery of an Earth-size planet orbiting another star in its habitable zone, we are now getting first glimpses of the variety of Galactic environments conducive to the formation of these small worlds," the astronomers wrote.

As a result, the path toward a more complete understanding of early planet formation in the Galaxy starts unfolding before us, they concluded in the paper that appeared in the Astrophysical Journal.