Scientists Thrilled to Find Water Vapor in Exoplanet's Atmosphere

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It may orbit a smaller star than our own sun, but K2-18b receives about the same amount of solar energy. M. Kornmesser/ESA/Hubble

The forecast for the planet known as K2-18b is rain. With a chance of life.

And although it's a slim chance, a newly published international study suggests the planet is literally drenched in potential.

Not only did researchers detect water vapor, but K2-18b also happens to reside in the "Goldilocks zone," a term used to describe a planet's distance from its sun that's neither too hot nor too cold.

"This represents the biggest step yet taken towards our ultimate goal of finding life on other planets, of proving that we are not alone," lead author Björn Benneke of the University of Montreal notes in a press release. "Thanks to our observations and our climate model of this planet, we have shown that its water vapour can condense into liquid water. This is a first."

Indeed, that combination of solar real estate and water vapor may make this Super Earth the most tantalizing target yet in the quest to find neighbors in the cosmos.

Although, at 111 light-years from Earth, it may take a while for us to get to their doorstep.

And even if we could traverse that vast stretch of space, there's a good chance we'd be disappointed when we get there.

Even from afar, K2-18b suggests a certain slant toward the strange. For one thing, the exoplanet that boasts about nine times the mass of Earth may have too much of a good thing. According to the researchers, there's so much hydrogen and water vapor in its atmosphere, it creates a thick, heavy veil.

Those crushingly high-pressure conditions, researchers note in the release, "likely prevents life as we know it from existing on the planet's surface."

K2-18b is mostly made up of very dense atmosphere, so it may harbor life — but "certainly not some animal crawling around on this planet. There is nothing to crawl on."

But there's plenty of space to build a dream. K2-18b, which was first discovered in 2015, joins an ever-expanding cast of candidates for alien life. In fact, NASA's Kepler Mission, which launched in 2009, has identified nearly 4,500 exoplanets that might fit the bill.

K2-18b, however, could be the first known planet to occupy the Goldilocks zone and contain water vapor. That vapor may even form rain clouds. And the planet gets plenty of sun. Although the star it orbits is smaller and cooler than our own, K2-18b's orbit is close enough to bask in about the same amount of energy as the Earth.

The trouble is scientists don't yet have the means to answer the most vital question about the exoplanet: Is anyone home?

For their paper, which has yet to be peer-reviewed, the team relied on data collected between 2016 and 2017 from the Hubble Space Telescope. Over that period, the planet passed in front of its star eight times — offering a telltale glimpse of water molecules in its atmosphere.

But as for what may lurk beneath, that may be a job for the James Webb Space Telescope. Fully assembled and scheduled for a March 2021 launch, the super telescope promises to paint the cosmos in a whole new light. Thanks to its specialized life-detecting equipment, we may finally be able to peer beyond K2-18b's heavy veil — and see if anyone is actually home.

"We are not quite there yet," Benneke says. "This is really exciting."