Earth-like planets common, study suggests

More than one-third of the planet systems known to exist outside of the solar system could contain Earth-like planets, according to a new computer model.

The computer simulations, conducted by researchers at the University of Colorado at Boulder and Pennsylvania State University, suggest such planets even those with water could be more common than previously thought.

The research, to be published in Friday's edition of the journal Science, focuses on a type of planet called a Hot Jupiter, a gas giant that orbits very near itsparent star even closer than Mercury orbits its star, the sun.

About 40 per cent of the approximately 200 planets that have been found outside the solar system are Hot Jupiters.

These planets are thought to form early in the life of a solar system and to migrate inward toward their parent stars.

As a Hot Jupiter moves toward the star, the study suggests, its gravity pulls bits of rocky debris away from the star.

The researchers say these rocky bits are likely to coalesce into Earth-like planets in orbits outside of the Hot Jupiters in a "habitable zone," an area scientists believe could harbour life.

The gas giant's trip toward the sun also causes turbulence that slows down the orbits of small, icy bodies on the outskirts of the solar system, causing them to spiral inward.

These icy bodies can provide water to the new Earth-like planets, even leading to oceans kilometres deep, the study says.

The team of researchers ran their simulations on a network of more than a dozen desktop computers. Each simulation began with a proto-planetary disc of more than 1,000 moon-sized bodies, both rocky and icy.

Each run of the program simulated 200 million years of planetary evolution and took more than eight months.