More than one-third of the giant planet systems recently detected outside our solar system may harbor Earth-like planets, scientists reported on Thursday.
A type of planetary system, which contains gas giants known as "hot Jupiters" orbiting extremely close to their parent stars -- even closer than Mercury to our sun, may trigger the formation of ocean-covered, Earth-like planets in a "habitable zone" suitable for life, according to the researchers from the Pennsylvania State University and U.S. space agency NASA.
The study was published in the Sept. 8 issue of the journal Science.
The hot Jupiters, better known as close-in giant planets, can push and pull proto-planetary disk material during their journeys toward the stars, the researchers said.
Smaller planets can form on either side of the giant planet, located in a habitable zone, as Earth is, according to the study.
At the same time, turbulent forces from the dense surrounding gas slow down the orbits of small, icy bodies in the outer reaches of the proto-planetary disk, causing them to deliver water to the fledgling planets. Such planets may eventually host oceans several kilometers deep.
Previously, scientists assumed that as hot Jupiters plowed through proto-planetary material on their inward migrations toward parent stars, all the surrounding material would be "vacuumed up" or ejected from the system, but based on a new computer model simulation, the researchers indicated these early ideas were probably wrong.
One of every three known planetary systems could have evolved Earth-like planets in habitable zones like the one the Earth is in, and some 40 percent of the 200 known planets around other stars may be hot Jupiters, the researchers concluded.
In addition, simulations showed that another kind of rocky planet could often form inside the orbits of hot Jupiters. Such a planet, known as a "hot Earth" with a radius twice that of our own Earth, was discovered in 2005 in a nearby star system.
Both hot Earths and Earth-like planets in habitable zones formed with large amounts of water, up to 100 times the water present on Earth today, the researchers said.
The models also indicated such water-rich planets would probably contain a lower percentage of iron than Earth which may be important for the evolution and possible oxygenation of evolving atmospheres.
The new research effort may allow planet hunters to determine "rough limits" indicating where to search for habitable planets in known systems of giant planets, according to the team.
"Upcoming space missions such as NASA's Kepler and Terrestrial Planet finder and ESA's COROT and Darwin will discover and eventually characterize Earth-like planets around other stars," wrote the researchers.
"We predict that a significant fraction of systems with close-in giant planets will be found to have a hot Earth or potentially habitable, water-rich planets on stable orbits in the Habitable Zone."