Water Found in Planet's Skies


Water has been detected in the atmosphere of an extrasolar planet, but a team of Harvard researchers hesitates to conclude that this represents a step in the process to find life beyond Earth.

Lowell Observatory Astronomer Travis Barman made the discovery by comparing theoretical models that he had developed with previously collected data on HD209458b, a large, gaseous planet located 150 light years away from Earth.

The data had been collected by Harvard researcher Heather A. Knutson and Assistant Professor of Astronomy David Charbonneau.

Although astronomers have been expecting to detect the presence of water vapor in the atmospheres of nearly all of the known extrasolar planets, most of these 200 or so planets orbit too closely to their parent star for observations to be made easily.

But Barman said he is “very confident” about his observations, which he announced on Tuesday.

“Our findings show strong evidence for water’s presence in HD209458b’s atmosphere,” Barman said. “Now that we know that water vapor exists in the atmosphere of one extrasolar planet, it’s probably safe to say that other extrasolar planets also contain water vapor.”

To develop his models, Barman used a technique called transmission spectroscopy, which examines the light from a parent star as it passes through the outer reaches of a planet’s atmosphere. By analyzing the absorption patterns of the star’s light, he was able to deduce the molecules present in the planetary atmosphere.

Charbonneau was less optimistic, saying that Barman did not conclusively prove water’s existence in the atmosphere of HD209458b.

“My concern is that Travis may be over-interpreting our data,” he said. “In our paper, we made it clear that the apparent variations with color that we tabulated could be due to the telescope and instrument, and thus might not be due to molecules in the planetary atmosphere.”

Knutson agreed, saying that Barman’s analysis appears to account for some, but not all, of the color-dependent features in the data that she and Charbonneau collected from the Hubble Space Telescope last year.

In 2001, Charbonneau led a team in making the first detection of an atmosphere on an extrasolar planet, using a technique similar to transmission spectroscopy.

When asked about Charbonneau’s criticism, Barman cited similarities between Charbonneau’s landmark findings and his own. “David used the exact same method, exact same instrument, exact same telescope, the exact same planet, and the exact same uncertainty in measurements to discover the existence of extrasolar planets,” he said. [SEE CORRECTION BELOW]

Charbonneau said that regardless of any discrepancies, Barman’s paper will help advance astronomy by forcing a closer comparison between predictions of atmospheres on extrasolar planets with actual data gathered by observatories.

CORRECTION: The April 13 news article "Water Found in Planet's Skies" incorrectly quoted astronomer Travis Barman. He said that Assistant Professor of Astronomy David Charbonneau had discovered an extrasolar planet's atmosphere, not that Charbonneau had discovered an extrasolar planet.