Watching the Skies

A new facility designed to scan space for exoplanets has just successfully completed its first observation run. The French-led Exoplanets in Transits and their Atmospheres (ExTrA) project is housed at the European Southern Observatory's (ESO) La Silla Observatory in Chile, and it is funded by the European Research Council and the Agence National de la Recherche in France.

ExTrA is no ordinary planet hunter. Its three 0.6 meter (1.98 feet) telescopes continually scan nearby red dwarf stars for signs of exoplanets by monitoring the amount of light they project. A dip in brightness could signal the passing of an orbiting exoplanet across the side of a red dwarf star that's facing the Earth. The ExTrA telescopes compare the brightness of each observed star with that of four other reference stars to help spot changes.

Originally, it would be difficult to spot smaller, Earth-sized exoplanets using this method. However, astronomers working at the project developed a novel approach that measures the brightness of a star in many different colors to derive more information.

“La Silla was selected as the home of the telescopes because of the site’s excellent atmospheric conditions,” ExTrA project lead researcher Xavier Bonfils said in an ESO press release. “The kind of light we are observing — near-infrared — is very easily absorbed by Earth’s atmosphere, so we required the driest and darkest conditions possible. La Silla is a perfect match to our specifications.”

Hunting for Exoplanets

Human fascination with the unknown — or, more concretely, with what can be known — is one reason astronomers have been hunting for exoplanets. Another is the desire to find a second Earth, one that could potentially host life now or perhaps in the future.

They scan the space beyond our solar system, looking for planets that are similar to the Earth in size and relative location to their respective stars. After identifying these exoplanets, the next step usually is figuring out through observation whether the planet could host life. The presence of water is considered a good sign that it could.

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In 2017, NASA announced that they had found seven potentially habitable exoplanets in a star system some 40 light-years away from the Sun. These were all Earth-sized planets, with a good number located in the habitable zone — the so-called "goldilocks zone" — of their parent star, TRAPPIST-1.

In September 2017, scientists working on Kepler's K2 mission found three exoplanets located in an area of their star system where life-sustaining atmospheres could form. These three "super-Earth" planets are considered good candidates for further observation.

ExTrA at the La Silla Observatory. Image Credit: ESO

At present, researchers have discovered and confirmed more than 1,000 exoplanets, mostly using the Kepler space telescope. The number is only expected to grow thanks to new tools and instruments such as the ExTrA telescopes and the PLANETS Foundation's ExoLife Finder (ELF) telescope. Other next-generation telescopes, including the James Webb Space Telescope (JWST) and the ESO's own Extremely Large Telescope (ELT), are also expected to contribute to this search.

As team member Jose-Manuel Almenara noted in the ESO press release, the ExTrA telescopes have the potential to help us learn more about the planets in the Milky Way and solar systems like our own, so we could soon have answers to some of our most basic questions about our corner of the cosmos.

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