Similar Sun System

From: Olga Bourlin (
Date: Thu Aug 16 2001 - 09:32:15 MDT

"Of all the solar systems that have been found, this is the one that looks the most like our own," said Debra Fischer, an astronomer at the University of California, Berkeley. "Hands down. Nothing else is even close." :
Thursday, August 16, 2001 - 12:00 a.m. Pacific

Far, far away shines a sun system much like ours

By Shankar Vedantam
The Washington Post

WASHINGTON - Astronomers have found a planetary system remarkably similar to Earth's - two planets in circular orbits around a star in the Big Dipper.

The star - about 45 years away if you hopped a ride on a beam of light - is similar to the sun in chemical composition. Astronomers say the circular paths and sizes of the two planets hint at the presence of smaller, Earthlike bodies in tighter orbits.

If such inner planets exist and are blessed with water, that could mean that life might flourish there. Even if that is not the case, scientists said the discovery boosts hopes that planetary systems with Earthlike planets eventually will be found.

"Of all the solar systems that have been found, this is the one that looks the most like our own," said Debra Fischer, an astronomer at the University of California, Berkeley. "Hands down. Nothing else is even close."

More than 70 planetary systems have been discovered around other stars, including three with multiple planets, but most have sharply elliptical orbits. Such orbits, which likely would freeze and heat the planet to extremes as the planet dives close to a star and then pulls far away, are poor candidates for life.

The planets around this star - dubbed 47 Ursae Majoris in the Big Dipper - are large, gaseous, Jupiterlike giants. If they had been circling our sun, their path would have been roughly between Mars and Jupiter, scientists said.

"For the first time, we have a star with two gas-giant planets that are far away from the star, and we know there isn't a gas-giant planet in the inner regions of the star," Fischer said. "... This is the only star that has a big empty zone in the habitable region around a star, the place where water could exist."

Astronomers in the past few years have begun a systematic search for planetary systems that resemble ours. They have been hindered by vast distances that have made it impossible to see planets directly in other star systems.

What astronomers can see are stars. As large planets revolve around their stars, they exert a gravitational pull that causes stars to wobble. The speed of the wobble indicates how long a planet takes to circle the star.

By focusing extremely precise measuring techniques at 47 Ursae Majoris, astronomers measured wobbles of 36 feet a second - about the speed of a human sprinter - and inferred the presence of one of the large planets. The other, larger and closer to the star, had been discovered previously.

By comparison, Jupiter exerts a wobble on the sun of 40 feet a second. Earth, much lighter, exerts a wobble of about 4 inches a second on the sun, Fischer said.

The tiny effect of small planets is what makes it impossible to use the technique to spot Earthlike planets around Ursae Majoris. Researchers can spot wobbles as small as 10 feet a second and are working on reducing the number to 3 feet a second, which will allow them to spot planets 10 to 20 times the mass of Earth.

Astronomers noted that large planets often imply the presence of smaller Earthlike ones. The solar system, for example, has two large gaseous planets - Jupiter and Saturn - and a host of smaller planets such as Earth, Mercury, Venus and Mars, that have orbits closer to the sun.

"Finding the large ones is like finding boulders and rocks strewn along the beach from afar," said Geoff Marcy, a professor of astronomy at the University of California, Berkeley, who also worked on the discovery. "If you see them a mile offshore, that means there's probably sand there, too."

Large, gaseous planets may also help create the proper conditions for life on smaller planets. In the development of our solar system, Jupiter played the essential roles of traffic cop and garbage disposal, said Paul Butler, a staff scientist at the Carnegie Institution of Washington.

Jupiter's enormous mass - larger than all other planets combined - sucked in meteors, comets and debris that otherwise would have pelted Earth constantly. And it enforced lane discipline - all the planets in our solar system have roughly circular orbits and revolve counterclockwise around the sun in a single plane.

"Jupiter acts as a bouncer in the solar system; it enforces circular orbits," said Butler, who worked with the Berkeley team on finding new planets. "If any planet's orbit should become noncircular, Jupiter will eject it."

Copyright 2001 The Seattle Times Company

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