Space scientists on Monday announced the discovery of what may be a rocky, Earth-like planet orbiting a star 15 light years away – a milestone in the search for a world outside the solar system that could sustain life.

The new planet, dubbed a “super-Earth” by the team that found it, is about seven times as massive as Earth and about twice the diameter. It orbits the star Gliese 876, located in the constellation Aquarius.

Until now, every extrasolar planet found has been larger than Uranus, the giant ice planet at the edge of our solar system. Two other planets previously had been found orbiting Gliese 876, a small red star known as an M dwarf, the most common type of star in the galaxy, but these were Jupiter-size gas giants.

The new planet’s size and mass suggests that it may be the first rocky planet, like Earth, that has ever been found orbiting a normal-size star. Researchers think it may resemble the inner planets of this solar system, made of nickel and iron.

“This is a big milestone, to get down to the region of rocky planets,” said team member Steven Vogt, a professor of astronomy and astrophysics at the University of California, Santa Cruz.

“We keep pushing the limits of what we can detect, and we’re getting closer and closer to finding Earths,” he said.

Even though the new planet is the closest analog to Earth yet discovered, it could not support life as we know it. Whirling around its star in just two days, it is far too close for water to exist in liquid form. Surface temperatures range from 400 to 750 degrees Fahrenheit.

“It’s not the place to go for a vacation,” Vogt said.

That hardly dimmed the excitement of the team, composed of researchers from the University of California, the Carnegie Institution in Washington, D.C., and the National Aeronautics and Space Administration’s Ames Research Center near Mountain View.

“Today’s results are an important step toward answering one of the most profound questions that mankind can ask: Are we alone in the universe?” said Michael Turner of the National Science Foundation, which helped fund the research.

The detection of most planets found outside the solar system, including the new one, known as Gliese 876d, could not be done by direct observation, because they don’t give off light. The presence of the planets is revealed by analyzing the subtle wobble in a star’s movement that is caused by the gravity of a nearby object in space. An orbiting planet tugs on its star.

Although technology is not yet advanced enough to see the new planet, the research team said that they were confident of their findings, which have been submitted to the Astrophysical Journal for publication.

There are three types of planets in our solar system: the rocky inner planets, consisting of Mercury, Venus, Earth and Mars; the gas giants, Jupiter and Saturn; and the intermediate planets like Uranus and Neptune, which are thought to be composed of rock, ice, water and other constituents. The scientific team thinks the new planet lies somewhere between the rocky inner planets and the mid-range ones.