Washington ? Astronomers have discovered what may be the smallest alien planet yet – a rocky “super-Earth” only four times heavier than our home planet.

It’s orbiting a small star at a distance that puts it in the so-called “habitable zone” – a region neither too hot nor too cold for liquid water and therefore suitable for possible life.

Scientists believe such Earth-like planets are the best hope for detecting evidence of living organisms beyond our solar system.

The tentative finding, which has yet to be confirmed, was reported during the May meeting of the International Astronomical Union in Cambridge, Mass.

The object is one of 45 potential new planets in the Milky Way galaxy recently discovered by the European Southern Observatory’s 140-inch telescope perched on a mountaintop at La Silla, Chile.

“The mass of the planets and the sheer number of them represents a huge step towards finding planets of the Earth’s mass, and ones that might be suitable for life as we know it,” Sara Seager, an astronomer at the Massachusetts Institute of Technology in Cambridge, said in an e-mail interview. “What amazes me is that these planets may be very, very common.”