On September 12th, at a conference on life in the universe hosted by Harvard University, David Charbonneau, an astronomer at that same university, gave a talk titled “The terrestrial planets of the smallest and closest stars”. The unofficial title, as revealed on his second slide, was “Small angry stars and the many godforsaken rocks which orbit them”.
Astronomers have now found more than 5,500 planets around other stars, or exoplanets, most of them detected by means of the small dip in the star’s light that happens when the planet passes across its face, and the planet’s shadow thus passes across the Earth. Hundreds of these sit in their parent star’s “habitable zone”, which means they orbit neither so close that any water on their surfaces would boil away, nor so far that it would be frozen. Since water is vital to every form of life known on Earth, such potential sogginess is much prized by scientists interested in whether some exoplanets might harbour life of their own.
What astrobiologists most want to do when they come across a planet in the “Goldilocks zone” is look at its atmosphere. The Earth’s atmospheric chemistry betrays the presence of life on its surface in a number of ways. The same should hold true for exoplanets that carry life. The launch in 2021 of the James Webb Space Telescope (JWST) brings with it the chance that such signs might be seen in planets around other stars. The prosaically named Extremely Large Telescope (ELT), presently being built in Chile and due to start work in 2028, will also be able to look at the atmospheres of nearby exoplanets.
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