The Tech - Online EditionMIT's oldest and largest
newspaper & the first
newspaper published
on the web
Boston Weather: 71.0°F | Partly Cloudy

Scientists Uncover Evidence of New Planets Orbiting Star

By Robert Lee Hotz
Los Angeles Times

An astronomer has found "irrefutable evidence" of at least two planets orbiting a nearby star - the first confirmed observation of planets outside the solar system humanity calls home.

What has scientists most excited, however, is that the finding suggests the formation of planets can take place around almost any star and that the galaxy may well be crowded with planets.

Astronomer Alexander Wolszczan at Pennsylvania State University confirmed the existence of the planets in orbit around an unusual neutron star located 1,200 light years away in the constellation Virgo. The star is one of just 21 known stellar objects, called millisecond pulsars, that spin thousands of times faster than typical stars, broadcasting powerful radio pulses as they revolve.

The star, known as PSR B1257+12, is an extremely small, massive body about 12 miles in diameter, that weighs as much as the Sun and spins faster than a kitchen blender. It is the cinder from an ancient supernova that once burned more brightly than any other object in the sky.

"The proof that objects of planetary size do exist outside the solar system indicates that our planets are not unique and uncommon anymore," Wolszczan said. "The evidence is such that there is no need to question the reality of this."

Wolszczan and his colleagues determined that one planet is about 3.4 times the size of Earth and is orbiting the star every 66.6 days; the second planet-sized object appears to be about 2.8 times the size of Earth and is orbiting the pulsar every 98.2 days.

Scientists said Thursday it was extremely unlikely that either planet could support life.

Wolszczan also reported the possibility that a smaller moon-sized object is orbiting closer to the star, but cautioned that those observations were not yet confirmed. That object appears to circle the pulsar every 25 days.

More than one scientific reputation has foundered on such announcements of new planetary systems.

At least five times in the past 30 years, news of such discoveries has been followed quickly by retractions, when errors in the data were discovered or when others could not confirm the initial sighting. In 1992, for example, one respected British astronomer had to tell his assembled colleagues that the planet he thought he had discovered the year before "just evaporated."

But Wolszczan's findings, which were published Friday in the journal Science, appear to convince many skeptical astronomers. He spent three years confirming the existence of the planets, which he first detected in the fall of 1991 with the help of Dale Frail of the National Radio Astronomy Observatory after 16 months of monitoring the unusual star.

The discovery apparently culminates a search that began with the invention of the first telescope centuries ago. But no one has actually laid eyes on the two planets with any optical instrument.

Instead, to find the planets, researchers used statistical analysis and detailed observations of the regular radio signals the pulsar emits. Wolszczan was able to detect the infinitesimal wobble caused by the gravitational pull of the planets whirling around the central star. The star sends out a radio signal 160 times a second with a precision greater than the most accurate atomic clock on Earth.

Wolszczan used the 305-meter-diameter radio telescope at the Arecibo Observatory in Puerto Rico to measure the arrival times of the pulsar's energy pulses. Unlike many of the other 550 known pulsars in the universe, these signals contained a subtle, periodic hesitation that strongly suggested the position of the star was changing in response to one or more large objects in orbit around it.

Further meticulous analysis revealed the effect of the planets' changing orbits as they passed each other in their journey around the strange sun, bearing out theoretical predictions. That was the test that other astronomers found most convincing.