One of the biggest questions in astronomy is whether there are other planets that could support life. To do this, astronomers must find planets whose surfaces contain liquid water, and they have just developed a new method to detect it.
A team of astronomers from the University of Birmingham, MIT and other institutions has found a new way to find water and life on exoplanets, or planets outside our solar system, by looking at the amount of carbon dioxide and ozone in their atmosphere.
Researchers have shown that if an exoplanet contains less carbon dioxide than neighboring planets, this means that there is liquid water on its surface. And if it also contains ozone, there is life.
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Researchers develop new method to find life in space
The researchers based their idea on the observation that Earth, Venus and Mars, all of which are rocky planets located in the Sun’s habitable zone, have very different amounts of carbon dioxide in their atmosphere. Earth is the planet with the least carbon dioxide, because its oceans have absorbed most of it over millions of years.
This process helped regulate the Earth’s climate and make it suitable for life. Venus, on the other hand, contains the greatest amount of carbon dioxide, because it has no oceans and the greenhouse effect is rampant there, making it extremely hot and inhospitable. For its part, Mars contains a moderate amount of carbon dioxide, but it is too cold and too dry to contain liquid water.
So the researchers thought that if they found a similar pattern of carbon dioxide variation in other planetary systems, they could identify planets where liquid water and possibly life can be found. They proposed a strategy to search for such planets, by first confirming that they have an atmosphere, then measuring the amount of carbon dioxide they contain. They suggested that this method would work best for systems that have multiple terrestrial planets of similar size and orbit, such as our own solar system.
“ Carbon dioxide is a very strong absorber in the infrared and can be easily detected in the atmosphere of exoplanets said Julien de Wit, an astronomer at MIT and one of the study’s authors. “ A carbon dioxide signal can therefore reveal the presence of exoplanet atmospheres “.
Once astronomers have determined that several planets in a system have atmospheres, they can measure their carbon dioxide content, to determine if one of them contains much less than the others. If so, the planet is probably habitable, meaning it has significant amounts of liquid water on its surface.
How to determine if the planet is inhabited?
Obviously, habitability conditions do not necessarily mean that a planet is inhabited. To determine whether life actually exists, the authors propose that astronomers look for another feature of a planet’s atmosphere: ozone.
On Earth, plants and some microbes help extract carbon dioxide, but to a lesser extent than the oceans. However, as part of this process, life forms emit oxygen, which reacts with photons from the Sun to turn into ozonea molecule much easier to detect than oxygen itself.
If a planet’s atmosphere shows signs of ozone and carbon dioxide depletion, then it is likely a habitable, inhabited world. The team estimates that the NASA/ESA/CSA James Webb Space Telescope, scheduled to launch in 2024, would be able to measure carbon dioxide, and possibly ozone, in nearby multi-planetary systems such as TRAPPIST -1, a system of seven planets orbiting a bright star, just 40 light years from Earth.