How the atmosphere of a planet outside the solar system was first discovered
Tamara Traubman
Astronomers believe they have made another important step in the study of distant planets, which are outside our solar system: a team of researchers was able, for the first time, to observe the atmosphere surrounding a distant planet. In addition to the observation itself, the researchers also performed a preliminary analysis of the composition of the atmosphere.
The atmosphere, observed by the Hubble Space Telescope, wraps the holiday planet around the Sun HD209458 and is about 150 light-years from Earth, in the constellation Pegasus. The initial chemical analysis of the planet's atmosphere was designed to discover, and indeed discovered, the chemical element sodium. The astronomers believe that in the atmosphere there is a greater prevalence of other elements, such as hydrogen and helium. But they tried to detect sodium first, because the team expected it to be present in the atmosphere and "easy to detect, even if it's in small amounts," one of the lead researchers, Dr. Timothy Brown, said in an official statement released by the team.
Prof. Zvi Maza from Tel Aviv University, who headed the multinational team that discovered the planet about three years ago, defined the discovery as "a very important and significant step". According to him, the discovery may be the first step on the way to further observations that will provide a more complete picture of the composition of the atmosphere of the planet studied in the current observation and the composition of the atmospheres of other planets. Details of the research should be published soon in the scientific journal "The Astrophysical Journal"
As Dr. Brown and other scientists have pointed out, Hubble was not specifically designed to study distant planets. When it was launched, about ten years ago, not a single planet outside the solar system had yet been discovered. But in the last decade, about eighty planets were discovered, most of them huge, orbiting relatively close suns. The planets cannot be seen even with the most powerful telescopes. But their existence can be inferred from fluctuations in the light emitted from the sun around which they pass. The oscillations are created as a result of the gravitational force that the two exert on each other.
In additional observations, made after the discovery of the holiday planet around HD209458, it was found that unlike other planets discovered outside the solar system, this planet passes in its orbit at a point between its sun and the Earth, like in a lunar eclipse. In each such passage, a small amount of light crosses the atmosphere and reaches the earth. The researchers decided to use the instrument stationed in Hubble and known as a spectrograph, to examine the light leaving the atmosphere. Each compound or chemical element in the atmosphere absorbs light differently, therefore there is a special pattern - a kind of personal signature - in the spectrum of light rays, which characterizes only them. The sodium signature is seen in the yellow-green colors of the spectrum.
Scientists working with Hubble and other telescopes on Earth are now examining other discovered planets, hoping to find similar defects. The method makes it possible to learn about distant planets details that until now were beyond the reach of researchers. It is possible to find out what is the mass of the planet (so far astronomers could only calculate the lower limit of the mass of the planet), what is its diameter, and as mentioned also to study chemical elements in the atmosphere.
Prof. Maza said that it is unlikely that life developed on this planet. All this because of its close proximity to the sun, which causes it to be extremely hot, and because its mass is about 220 times greater than the mass of the Earth, so the gravity there is also inhospitable to life. However, he added that the study of the composition of the planet's atmosphere could - indirectly - teach about the manner of its formation.
"The new findings are just a precursor to the discoveries on the way," said Dr. Brown, "especially considering that new telescopes that will be placed on Earth and in space in the next decade will be designed to specifically study planets outside the solar system." Astronomers studying the atmospheres of other distant planets hope to find carbon dioxide, water vapor, ozone and methane in them in the future. "If you can locate signatures of all four of these on the same planet," said Brown, "you can build very convincing arguments that this planet allows for the development of life, and maybe life actually exists on it."
