Viernes 21 de Junio de 2002, Ip nš 17

Planetary system found that resembles ours
Por Richard Stenger

The announcement came Thursday as astronomers described the discovery of 15 new planets in other star systems, including one that resembles Jupiter around a sun-like star.

Known as 55 Cancri, the star system is about 41 light years away and will likely remain a place of particular interest as astronomers begin to look for planets like Earth in the coming years.

"This planetary system will be the best candidate for direct pictures when the Terrestrial Planet Finder is launched later this decade," said planet hunter Debra Fischer of the University of California, Berkeley, referring to one of NASA's next generation of space telescopes.

The newly discovered jovian-like world takes about 13 years to revolve around its parent star, compared with almost 12 years for Jupiter's journey around the sun.

The new planet has some significant differences. It is roughly four times the mass of Jupiter and its orbit is slightly elongated.

"We haven't found an exact solar system analog, which would have a circular orbit and a mass closer to that of Jupiter. But this shows we are getting close," said Paul Butler of the Carnegie Institution, one of the leaders of the study, funded by NASA and the National Science Foundation.

But the orbit of the Jupiter-like planet is stable enough to foster a benign, life-friendly environment in the inner solar orbit, the astronomers said.

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.

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.


  13/06/2002. CNN.