Water found around a hot Jupiter

A new method could help to find water on planets all over our Galaxy


Credit: Alexandra Lockwood/CALTECH

A new technique could help discover many exoplanets with water

Astronomers using a new spectroscopic technique at the Keck Observatory, Hawaii have discovered water in the atmosphere of a nearby exoplanet. Tau Böotis b, is a Jupiter mass planet orbiting close to its host star and it’s hoped the technique will help discover how many other planets in our Galaxy also have water.

Scientists analysed light from the planet’s host star, trying to extract the unique signature of water. When a star has a planet orbiting around it, it gets pulled off balance slightly, causing it to wobble. This new technique uses this movement to tell which features are from the star and which are from the planet’s atmosphere.

This isn’t the first time water has been found on an exoplanet. In December 2013 water was discovered on five other hot Jupiters, but these were planets that transited – or passed in front of – their host star. Unfortunately, most exoplanet orbits are not in the correct orientation to transit, and so can’t be analysed this way.

The new method offers a way to examine the atmospheres of hundreds of exoplanet systems that would otherwise be unobservable, looking for not just water but many other chemicals as well.

However, it does have some limitations. The technique only works on planets that are very large and very close to their star.

"While the current state of the technique cannot detect earthlike planets around stars like the Sun,” says Geoffrey Blake, a professor of cosmochemistry at the California Institute of Technology, “with Keck it should soon be possible to study the atmospheres of the so-called 'super-Earth' planets being discovered around nearby low-mass stars, many of which do not transit. Future telescopes, such as the James Webb Space Telescope, will enable us to examine much cooler planets that are more distant from their host stars and where liquid water is more likely to exist."



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