Astronomers have developed a new way to probe the atmospheres of exoplanets, opening up a whole class of the distant worlds to investigation.
According to the Southern European Observatory, a team using the ESO’s Very Large Telescope have been able to tease out clues about the atmosphere of the exoplanet Tau Boötis b, despite the bright glare of the planet’s parent star. The star lies in the direction of the constellation Boötes.
Some exoplanets orbit their star in a plane which brings them directly in front of their star when viewed from the Earth. Such planets’ atmospheres have been previously examined by analyzing the changes that occur in the star’s light as it passes around the planet and through its atmosphere.
However, most exoplanets, like Tau Boötis b, orbit in planes which do not bring them between their star and the Earth, meaning that their atmospheres cannot be examined in the same way. In order to study this larger class of exoplanets, astronomers needed a new method. Because such planets are usually detected by their gravitational effects, all that has previously been known about them is their approximate masses.
Now, astronomers from the ESO claim to be able to glean information about these exoplanets by examining their light directly, by using the Very Large Telescope and a particular instrument called CRIRES. Lead author Matteo Brogi, of Leiden Observatory in the Netherlands, says, “Thanks to the high quality observations provided by the VLT and CRIRES we were able to study the spectrum of the system in much more detail than has been possible before.”
Examining the light from an exoplanet directly is difficult, as at our distance the light from the planet is extremely dim when compared to the overwhelming brightness of the parent star. The effect is somewhat similar to trying to view, from a distance, the gleam of a candle sitting next to a car’s headlights. Brogi notes, “Only about 0.01% of the light we see comes from the planet, and the rest from the star, so this was not easy.”
In order to separate the planet’s signal from the light of the star, and from the interference of the Earth’s atmosphere, the astronomers made use of the planet’s changing motion around its star. As the planet circles its star, it moves towards Earth for half of its orbit, and away for the other half. These changes in motion produce regular shifts in the planet’s contribution to the combined light of the planet and the star. By separating out those regular shifting portions of the light, astronomers can separate the light coming from the planet from the light coming from the star. Examining the signals in the planet’s light, as well as the characteristics of the way the planet’s light shifts, the scientists can elucidate details about the planet’s atmosphere, as well as determine its orbital plane and more accurately estimate its mass.
In addition to showing that this technique can be applied to study of exoplanets, the researchers hope that their technique may contribute to the search for an answer to the question of whether life exists on any planets outside of the solar system. Ignas Snellen, a co-author of the paper, says, “This study shows the enormous potential of current and future ground-based telescopes, such as the E-ELT. Maybe one day we may even find evidence for biological activity on Earth-like planets in this way.”
The astronomers present their research in a recent paper in Nature.