Planet discoveries excite speculation

Press, 5 August 1988, Page 6

Planet discoveries excite speculation

NZPA-AP Baltimore United States and Canadian astronomers have found 10 planet-like objects orbiting distant stars, a discovery that intensifies speculation about the existence of life beyond the Earth.

In reports yesterday at the International Astronomical Union assembly, astronomers from the Smithsonian Astrophysical Observatory said they had found “what might be a very large planet” orbiting a star 90 light years away.

In an independent study, an astronomer from the University of Victoria, British Columbia, said he has found evi-

dence of planets orbiting nine stars, and suggested that as many as half of the stars in the Milky Way galaxy may have “planetary companions.” Bruce Campbell, chief of the Canadian team, said his result “showing that the majority of stars in the galaxy perhaps have planetary systems could be interpreted as a sign that there are also Earth-like planets suitable for life, but we have no evidence of that at all.”

David Latham, leader of the Smithsonian team, said: “It makes it easier to speculate than it was a few years ago when there were zero planetary candidates.

“We can start to speculate now about how often life evolved.” Both teams of astronomers made the discoveries by analysing the colour shift of light collected from stars. Light from a distant source changes colour slightly if the light source is moving. It shifts toward red if it is moving away, and toward blue if moving toward the observer.

By carefully measuring this shift, the astronomers are able to detect wobble, or movement of the stars. This movement can be caused only by the gravitational effect of a nearby body, and the velocity of the movement allows the

scientists to calculate the size of the object.

Mr Latham said the planet-like object he found is about 20 times the size of Jupiter, and is orbiting so close to star HD 114762 that it would be “much hotter than an oven.”

“It’s not a place you would go to look for life,” he said.

The object,, Mr Latham said, is about 3000 times the size of Earth and is on the very edge of what is commonly thought to be the maximum size for a planet. Star HD 114762 is 90 light years — about 840 trillion kilometres — from Earth. t

Mr Campbell said he and his Canadian group used a technique even more sensitive than the instruments used by Mr Latham and were able to find nine planetary objects after studying just 18 stars.

The clearest data, he said, show that a large planet orbits a star called Tau Ceti.

“We see in the star the effects of a companion sized on the order of Jupiter,” Mr Campbell said.

Eight other planet-like objects were found about other stars, he said, but the team was unable to make a precise measure

of their size.

"We can only infer masses on the order of 1 to 10 times that of Jupiter,” Mr Campbell said.

All of the stars studied by the Canadian team are bright, about magnitude 4. They all are similar in size to the sun, and all are within 100 light years, about 930 trillion kilometres, from Earth.

Mr Latham’s study concentrated on very faint stars. HD 114762 is of a 7 magnitude, too faint for sighting by the naked eye. Stars grow fainter as the number increases on the magnitude scale. A magnitude of 6 is the faintest visible to the naked eye.