part 2
Jupiter, the largest planet in our solar system, is thought to have protected terrestrial life in its infancy, ingesting dangerous hordes of comets before they collided with our planet.
Dozens of so-called exoplanets have been detected in recent decades. They tend to travel in highly elliptical and contorted orbits, usually much closer and faster than large planets in our solar system.
For example, a planet slightly less massive than Jupiter, discovered earlier by the same scientific team, orbits 55 Cancri every two weeks from a distance closer than Mercury to the sun.
Theoretical models suggest that a small rocky world like Earth could survive in an orbit between the two planets.
Artist's concept of an exoplanet
But whether a terrestrial planet lurks near the star will remain a matter of speculation for some time. The hunt for exoplanets has turned up only gas giants so far because of the limits of current search methods.
By observing the gravitational tug on stars over time, astronomers deduce the existence of exoplanets as well as estimate their mass, orbital paths and revolution periods.
Ground-based observatories and space telescopes like the Terrestrial Planet Finder might allow scientists to directly detect planets, including small ones like our own.
In the meantime, refinement of the star-wobble technique should keep astronomers plenty busy. Fischer, Butler and colleagues, the most experienced team of planet hunters, are finding increasingly smaller planets in their ongoing survey of more than 1,200 stars.
The new discoveries, announced at NASA headquarters in Washington, D.C., include another planet around 55 Cancri, a star visible to the naked eye in the constellation Cancer; and the smallest known exoplanet, one near the star HD49674 with less than half the mass of Saturn.