Atmosphere of extrasolar planets rather Marslike than Earthlike?

Computer model gives new insights into laws of atmospheric chemistry

What does the atmosphere look like on extrasolar Earth-like planets? © NASA
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More and more extrasolar planets are being discovered. But how does it look like this? What kind of atmosphere do you own? An answer could now be provided by a computer model developed by an American researcher. Based on data from the planets of the solar system, it also allows conclusions to other celestial bodies.

The recent discovery of an Earth-like planet around the star Gliese 581, 20 light-years from Earth, triggered worldwide speculation about how the surface and atmosphere of this planet could be constructed. Bruce Fegley, a professor of Earth and Planetary Sciences at Washington University in St. Louis, has now created a computer model based on new data from space missions but also from spectroscopic data from terrestrial telescopes, that certain laws and patterns in the atmospheric chemistry of planets shows.

More water on sun-far planets

Current research indicates that there is a clear atmospheric trend in the planets within the solar system: "The further you go outside, the more water you find, " explains Fegley. While Jupiter is extremely poor in water, there are traces of water vapor in the atmosphere of Saturn, albeit less than other gases. Uranus and Neptune, on the other hand, the two outermost planets, are considered very rich in water.

"The theory assumes that the gas giants, Jupiter, Saturn, Uranus, and Neptune, have primary atmospheres, which means their atmospheres were captured directly from the solar nebula during planetary formation, " Fegley said. As he explains, Jupiter has more hydrogen and helium and less carbon, nitrogen, and oxygen than the other gas giants, making it more sun-like than the other gas planets. "Jupiter, as observations of the Galileo probe show, is depleted of water." The outer gas planets, on the other hand, are best described as water planets with relatively thin gas shells.

Secondary atmosphere through outgassing

In contrast to the gas giants with their so-called primary atmosphere, earth-like, solid rock planets such as Venus, Mars and Earth have secondary atmospheres: they were formed after the formation of planets by outgassing the rock. Using photochemical models and chemical data, Fegley, together with his colleague Laura Schaefer, developed a model that can use the laws of these outgassing to determine how the atmosphere of extrasolar Earth-like planets is composed. display

More like Mars or Venus

"Because the composition of our galaxy is relatively uniform, most of the stars are similar to the sun, and rich in hydrogen with approximately equal proportions of solid elements, we can predict what these planetary atmospheres might look like.", says Fegley. "I believe that the atmospheres of extrasolar Earth-like planets resemble those of Mars or Venus rather than Earth."

On Earth, photosynthesis of plants accounts for a large part of the oxygen in the atmosphere. Without them, the air would primarily consist of nitrogen, carbon dioxide and water vapor. Compared to the 21 percent oxygen of the earth's atmosphere, Mars is barely a tenth of a percent. This comes from the photochemical decomposition of carbon dioxide by UV light.

"I see Mars today as a great natural photochemistry laboratory, the Venus for thermochemistry and the soil for biochemistry, " explains Fegley. "Mars has such an atmosphere that UV light can penetrate to the surface before it is absorbed. On Earth, most of this light is trapped by the ozone layer. The hell of Venus, on the other hand, is so dense that the clouds cover almost everything.

(Washington University, June 20, 2007 - NPO)