The wobble, by indicating some object is exerting a gravitational influence on the star, is an indirect way of detecting planets.
The wobble in this star, HD 209458, was observed on November 5 by Geoffrey Marcy, a professor of astronomy at the University of California, Berkeley, along with Paul Butler and Steve Vogt.
But back in September, exo-planet hunters Charbonneau and Brown had already observed the dip in starlight from the planet passing in front of HD 209458.
And their observations were more thorough, covering two full transits (on September 9th and 16th) of the planet across the disk of the star.
By November, when Henry zeroed in on the star, it was dipping low into Earth's horizon, where atmospheric disturbances make viewing difficult. Henry had programmed his computer to stop observing at a certain hour, and so only about half of the transit was recorded.
Charbonneau and Brown, who also worked with David Latham from Harvard-Smithsonian and Michel Mayor from the Geneva Observatory, did not issue an immediate press release.
Instead, they submitted their work to Astrophysical Journal Letters, a peer-reviewed journal. On November 23 -- seven days after the other group's news was widely reported -- the paper by Charbonneau and his colleagues was accepted for publication in the January 20, 2000 issue.
A paper by Henry, Marcy and their colleagues has since been accepted for publication in the same issue of the journal.
An apology
In an interview, Charbonneau said he was initially concerned over the timing of the other group's press release, because Henry, Marcy and their colleagues knew of the parallel research that was going on.
Marcy has since issued an apology, and Charbonneau said "we feel fine" about how it has all worked out.
"In the scientific community, we've gotten the recognition we deserved," Charbonneau said. "In terms of the general press, that probably will never be recaptured. But that's fleeting."
While he said "it would have been nice to have our names in the papers," Charbonneau added that he didn't really pay much attention to the coverage.
"I was busy writing up our paper and analyzing our data," he said.
Henry said the dual discoveries, whose results were nearly the same, are useful in providing confirmation that the technique works.
The fact that two groups made similar findings at nearly the same time reflects the odds under which they both worked. Henry explained that because the odds of spotting the transit of a planet orbiting close to a star are about 1 in 10, the time was ripe.
"It was the 10th system I had searched for a transit," he said. "The odds were beginning to suggest I should see a transit."
Details of the observation
The new method for observing distant planets, used by both groups, involves measuring light emissions from a star while a suspected planet passes in front of the star during its normal orbit.
Researchers first estimate the diameter of the host star, then by measuring the dip in starlight and the duration of the transit, they can estimate the planet's size.
For Charbonneau and Brown, the more complete observations allowed for what Charbonneau says is a more accurate estimate of the planet's size.
They noted a 1.5-percent decrease in starlight, which lasted about 2 hours, and calculated the planet to be about 1.27 times the diameter of Jupiter -- but with a density less than Saturn, the least dense planet in our solar system. The planet orbits the star every 3.5 days.
Henry had figured the planet to be slightly larger than what Charbonneau's calculations show. "There really aren't any significant differences in our derived properties," he said.
The star, HD 209458, is 153 light-years away (roughly 1.4 million billion kilometers or 859,000 billion miles) in the constellation Pegasus.
Researchers say it is about the same age, color and size as our sun. It is near the star 51 Pegasi, around which the first extrasolar planet was discovered in 1995 (using the indirect method of stellar wobble).
Earlier this month, British astronomers used yet another method to glean important clues about a different extrasolar planet.
Though the method is unconfirmed, the team appears to have discerned starlight reflecting off the planet, providing even better direct measurements of an extrasolar planet's size and mass.
The method, still unconfirmed, would be a first step toward understanding the composition of exo-planets.
"By measuring the amount of light reflected you can get a feel of whether water or methane are present in the atmosphere," Charbonneau said.
He added that the technology needed to find Earth-like planets, which would be harder to spot because they would be smaller and farther from their stars, is about a decade away and would likely involve space-based observatories.
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