Detection of extra solar planet’s atmosphere might help in finding extraterrestrial life

December 7th, 2007 - 1:05 pm ICT by admin  

Washington, Dec 7 (ANI): Astronomers have made the first ground-based detection of the atmosphere of a planet outside our solar system, which might turn out to be an incremental step in finding life in the universe.
The extra solar planet, which orbits HD189733, a star about 63 light-years away in the constellation Vulpecula, was observed using the Hobby-Eberly Telescope (HET) at McDonald Observatory in University of Texas, Austin, by astronomers Seth Redfield, Michael Endl, William Cochran and Lars Kosterke.
The work is believed to be an important step in finding life in the universe, falling between the initial detections of planets around other stars (known as ‘extra-solar planets’ or ‘exoplanets’), and the anticipated discovery of planets similar to Earth.
“What we all want to find is a planet with an Earth-like atmosphere,” said Redfield.
The data analysis for the detection involved studying hundreds of observations spread over a year, taken under different conditions.
It was found that the planet is 20 percent more massive than Jupiter, and orbits very close to its parent star (more than 10 times closer than Mercury is to our Sun).
From Earth’s line of sight, the planet passes directly in front of the star on each orbit. It was this ‘transit’ property that allowed the planet’s discovery in 2004 by Francois Bouchy of France ’s Laboratoire d’Astrophysique de Marseille , and the detection of its atmosphere in 2007 by Redfield.
That means this planet, HD189733b, is what’s known as a ‘transiting extra-solar planet.’
According to Redfield, the research team had to go for many transits to detect the atmosphere of the recently discovered planet, for which they studied 11 transits over the course of a year with HET and its High Resolution Spectrograph.
To obtain the planet’s ‘transmission spectrum,’ and thus the chemical composition of its atmosphere, the team used what they call “a very straightforward” technique.
“Take a spectrum of the star when the planet is in front of the star,” said Redfield. “Then take a spectrum of the star when it’s not. Then you divide the two and get the planet1s atmospheric transmission spectrum,” he added.
In the end, it was found that the extra-solar planet’s ‘transmission spectrum’ from HET was much higher resolution than that previously made with Hubble Space Telescope on a different planet.
Though this technique is straightforward, it is not easy, as the light blocked by the planet is a mere 2.5 percent of the star’s total light, plus another 0.3 percent for the planet1s atmosphere.
“Each time the planet passes in front of the star, the planet blocks some of the star’s light,” said Redfield. “If the planet has no atmosphere, it will block the same amount of light at all wavelengths. However, if the planet has an atmosphere, gasses in its atmosphere will absorb some additional light,” he added.
As for the composition of the planet’s atmosphere, it is predicted that sodium atoms should be present in it. The atmosphere of the planet will absorb more starlight at those wavelengths that correspond to specific transitions of the sodium atom.
“This causes the planet to appear larger, since we now ’see’ the planet plus the atmosphere, and we measure more blocked light from the star,” said Redfield.
When studying the planet at the particular wavelength of the sodium transition, the planet appears about 6 percent larger than at other wavelengths. The detection of sodium was possible because there’s a lot of it there, and the atomic transition is strong and falls within the visual range that ground-based telescopes can detect.
“Many other atomic and molecular constituents of the atmosphere may be studied in a similar way, including potassium and hydrogen,” Redfield said.
“I look forward to the detection of other gasses around this planet,” Lambert said.
“It is just breathtaking how fast the progress in the field of exoplanets is. We have arrived at a point where we can study the composition of the atmospheres of ‘hot Jupiters’ in great detail,” said Redfield1s collaborator, Michael Endl. “The HET is not only a planet finder now, but also a great tool to examine the atmospheric features of transiting extrasolar planets with unprecedented resolution,” he added. (ANI)

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