Advertisement
Share

Planet Believed Found Beyond Solar System

TIMES SCIENCE WRITER

Scientists have discovered a distant planet where virtually no one would have expected it to be, orbiting a pulsar star that was born during one of the most violent events the universe has to offer, according to research published today. If confirmed, this would be the first planet discovered beyond our solar system.

A team of astronomers from the University of Manchester at Jodrell Bank, England, said they found the planet, believed to be at least 10 times the mass of Earth, orbiting a young pulsar 30,000 light years away.

The planet is too dim to be seen, but the scientists said they are convinced it is there because the extremely dense star, called a pulsar because it pulses radio signals, wobbles in a way that can best be explained by the gravitational tug of a nearby planet.

If this discovery holds up, it means that planets can form under the most unfavorable conditions and should be common throughout the universe, thus enhancing the chances of life existing elsewhere.

Advertisement

It would also mean that some astrophysical concepts cherished by astronomers will have to be revised. And if it turns out that there is no planet, the pulsar it is believed to be orbiting must be a very bizarre object, scientists said.

Either way, according to scientists familiar with the work, the discovery promises to be an immensely important one. The finding was reported in today’s issue of the science journal Nature.

This is the latest in a series of claims in recent years by scientists who believe they have discovered distant planets, but none of the previous claims has been confirmed by subsequent research.

The search for other planets has become a consuming passion for a number of astronomers because of the implications for the existence of extraterrestrial life.

It is a difficult search because if other stars have planets, the planets are so dim compared to their host star that they cannot be seen with optical telescopes. The only way to find them is through some unusual characteristic of the star that could only be caused by a nearby planet.

The scientists announcing the discovery today, including Andrew G. Lyne, a leading authority on pulsars, are highly respected experts in radio astronomy. They studied their data for five years before revealing their results.

Lyne is “one of the most experienced pulsar observers,” said Caltech theoretical astrophysicist Roger Blandford. “I’m sure they have worked through all the things that would worry one about a surprising result like this.”

Blandford said he feels comfortable with the observations, and he believes the “least implausible” explanation for the wobble detected by the British astronomers is “the presence of a companion body.”

Advertisement

“It’s a very exciting observation,” he said.

Scientists said there is no way life could exist on this particular planet because of violent events in its recent past. But that does not lessen its importance, because if confirmed it “will challenge some, perhaps several, fundamental aspects of our views of the evolution of stellar and planetary systems,” David Black, director of the Lunar and Planetary Institute in Houston, said in an accompanying article.

Other scientists were astounded by the discovery.

“It’s weird, because it’s not a likely place to find a planet,” said Stephen P. Maran, an astronomer and spokesman for the American Astronomical Society.

Advertisement

By studying the only planetary system known to exist--our own--scientists have concluded that planets form by the coalescence of dust and gas orbiting a star, such as the sun. That theory, however, leaves little room for planets to exist around pulsars, which are believed to form after a “progenitor” star exhausts its fuel, collapses and explodes.

During the explosion, called a supernova, matter is believed to compress into the center of the exploding star, forming a neutron star. A neutron star is only about 10 miles in diameter and consists almost entirely of neutrons packed so tightly that a teaspoonful would weigh billions of tons.

Some neutron stars further evolve into pulsars that spin incredibly fast and emit radio signals that sweep across the heavens like a beacon from a lighthouse. If the Earth lies in the path of that beacon, the radio signals will be received here every time the pulsar sweeps past, in this case three times every second.

What puzzles the experts is that a stellar explosion sends out a shock wave that should sweep the neighborhood clear of debris, including any planets that might have been orbiting the dying star. If by some miracle a planet were to survive the explosion, its orbit at least should have been severely disturbed, but the newly discovered planet is in a nearly circular orbit and about the same distance from the pulsar as Venus is from the Sun.

Advertisement

So if the planet is left over from the progenitor star, the 1.2 million-year-old pulsar must have formed in a way other than what modern theory predicts, and that will lead to a “revolution” in astrophysics, Black maintains.

The pulsar, known only by the designation PSR1829, was discovered in 1985 while astronomers at Jodrell Bank were surveying the northern region of the Milky Way Galaxy. In all, 40 pulsars were discovered during the survey, but there was something quite different about PSR1829.

The astronomers found that the radio signals did not always arrive at the time they had been expected. For about three months they arrived a little early, followed by three months of arriving a little late. Then the cycle repeated.

After studying that cycle repeatedly, the scientists concluded that the irregularity was caused by a planet orbiting the pulsar.

Advertisement

They reached that conclusion on the basis of a common understanding of how orbiting bodies affect each other. A planet does not revolve precisely around a star. Instead, the two bodies revolve around the center of their collective mass. That would cause a star to oscillate, or wobble.

The timing of the signals indicates that PSR1829 is indeed oscillating, moving slightly closer to the Earth when the planet is between the Earth and the pulsar, and slightly away when the planet is on the other side.

And that, the scientists concluded, could account for the change in the time it takes the radio signal to travel to Earth.

One other explanation, according to the Astronomical Society’s Maran, is that as the pulsar spins it “might also be slowly twisting back and forth due to some strange effect in the inside of the star.”

Advertisement

“The argument against that,” he added, “is that more than 300 pulsars have been studied, and none of them show this effect.”

The discovery could be confirmed by other astronomers, using similar radio measurements. Ideally, however, it should be confirmed by scientists using different techniques and different equipment--such as optical astronomers who are able to measure the oscillation of the star, or infrared astronomers who could detect heat emitted by the planet.

But in this case the planet and the pulsar are so far away that infrared emissions would be too weak to be detected, Maran said. And changes in the position of the pulsar caused by the rotating planet would be so slight that no current instruments on Earth could measure them.

Finding a Planet

Advertisement

British scientists who have been studying 40 objects known as pulsars found that the radio signals from one, called PSR 1829, sometimes arrive at the Earth slightly earlier or later than they should have. From this irregularity, they have concluded that a previously unknown planet exists.

The Planet and the Pulsar

* A pulsar normally emits regular radio signals.

* But in this case, the gravitational influence of the planet is believed to be causing the pulsar to oscillate, or wobble.

Advertisement

* The pulsar’s wobbling is causing a variation in the time it takes the radio signals to reach the Earth, indicating the presence of a planet.

Creation of a Pulsar

A. Pulsars are formed when a red giant “progenitor” star exhausts its fuel and collapses.

B. The star explodes violently into a supernova, in which the core is compressed into a neutron star.

Advertisement

C. If the neutron star spins, it creates a powerful magnetic field that sweeps the heavens like a beacon from a lighthouse. When this occurs, the neutron star becomes a pulsar.

New Planet: About 10 times the mass of Earth.

Earth: About 8,000 miles in diameter.

Sun / Center of Milky Way / Pulsar and Planet: The pulsar and the planet are about 20,000 to 30,000 light years from Earth, in the direction of the center of our galaxy.

Advertisement


Advertisement