On November 27, 2001, astronomers made the first chemical analysis of the atmosphereof an exoplanet, a planet outside out solar system. The discovery was made using the Hubble Space Telescope using an interesting new method.

The Method Used

The planet in question (see below) happens to pass in front of its star (seen from Earth. This means that the light from the star is filtered through the planet's atmosphere before reaching us. By using spectroscopy, the chemical composition of the atmosphere can be determined.

Only a small portion of the spectrum from the star has actually been studied so far, and the result shows quantities of sodium. Further studies will be done in different parts of the spectrum to determine other atmospheric components.

The Planet

The planet was first discovered in 1999 by the slight gravitational pull it has on its sun. It is orbiting HD 209458 - a yellow, sun-like star - at a very short distance. In fact, it only uses 3,5 days on one orbit! This is incredible in itself, given that the planet in question is a gas giant with approximatly 70% of Jupiter's mass.

HD 209458 is about 150 light years from us, in the constellation Pegasus.

How Is This Significant?

This discovery opens up a new channel for space exploration. Categorising the known extrasolar planets according to their atmospheres will probably be an important job in the near future.

The most interesting thing astronomers will be looking for are signs of gases known to be traces of life. In particular, unstable gases present in an atmosphere is a giveaway of "something" producing it. Think about oxygen in our atmosphere. Without oxygen-producing lifeforms, the oxygen would quickly react and disappear. This is exactly the kind of scenario scientists hope to find on other planets.

Source: NASA news (original article: http://www.gsfc.nasa.gov/news-release/releases/2001/h01-232.htm)

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