Water vapor signal detected on distant planet

Written by theregister.com on May 1, 2021. Posted in Current News

Image: NASA Exoplanets

Evidence of what was once possibly water vapor has been detected in the atmosphere in a distant world for the first time – though one of the scientists involved in the discovery told us this would-be interstellar getaway is “completely inhospitable.”

Wasp-33b, spotted in 2015, is a hot and huge Jupiter-ish gas giant. Located about 400 light-years from us, its orbit is so small that a single year on this alien world lasts a little over 24 Earth hours. The short distance between itself and its sun, HD 15082, means that it bears the brunt of the star’s heat.

“The atmosphere is already over 2,000 degrees Celsius, as it is so close to its host star – a distance that would place it well within the orbit of Mercury to our Sun,” said physics assistant professor Neale Gibson, co-author of a paper published (preprint) in The Astrophysical Journal Letters detailing Wasp-33b.

“This would already make the planet completely inhospitable; it means that there is no liquid water anywhere on the planet, rather we expect water in the atmosphere to be in gaseous form, i.e water vapor.”

Technically speaking, Gibson, who is based at Ireland’s Trinity College Dublin, and his colleagues around the world detected hydroxyl radicals (OH), which are formed when water vapor breaks down. The team believes any water on the gas giant has evaporated to become water vapor in its atmosphere, and the extreme conditions strip away the vapor to leave the discovered hydroxyl radicals.

“This is the first direct evidence of OH in the atmosphere of a planet beyond the Solar System,” said Stevanus Nugroho, who led the research, who is a researcher at Japan’s Astrobiology Center. The idea of water boiling on exoplanets may not sound so surprising, though it’s the first time astronomers have direct evidence of that happening outside our system.

Hydroxyl radicals have only now been discovered around an exoplanet partly due to their scarcity, and partly because the techniques for analyzing chemical components on impossibly faraway worlds have improved.

“I would say it’s both rare and difficult to measure,” Gibson told us. “Everything to do with looking at exoplanet atmospheres is very hard, as the signals are just so small relative to the brightness of the host star. Over the last ten years or so we’ve become much better at observing atmospheric signals due to a combination of new techniques and new instruments on our telescopes.”

“Hydroxyl will only be seen in a subset of planetary atmospheres – at least at this signal strength – so in this sense it is more rare than other [chemical] species, and is why this is the first time we can detect it.”

Chemical compounds are detected through spectroscopy, which involves watching which portion of light is absorbed or emitted by matter. Since elements can only absorb or emit certain wavelengths of light, these patterns help identify which compounds or radicals are on Wasp-33b.

The InfraRed Doppler (IRD) instrument on the 8.2-metre-diameter Subaru Telescope in Hawaii allows the team to separate the light signals emanating from the exoplanet from its parent star. It’s tricky since the star’s light is so much brighter than its exoplanet.

The ultimate goal, Gibson told us, is that astronomers can improve these techniques for more advanced telescopes that they’ll be able to directly detect oxygen in the atmospheres of exoplanets within the next two decades.

“The other thing that we hope to do long term, is use these same techniques to look at cooler, rocky, planets, much more like the Earth. To do this we will have to wait until next-generation telescopes like the European Extremely Large Telescope,” he said.

“In principle the same way we can detect OH, we might be able to detect molecular oxygen, which combined with other gases could potentially signal signs of life. We’re a while away from being able to do this, but hopefully in the next 10 to 20 years this will become a possibility.”

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