Scientists have found water vapor on a ‘habitable zone’ planet

Federico Mansilla
Setiembre 12, 2019

And aside from water vapor, its atmosphere contains mostly hydrogen gas - a molecule that makes up less than 1 part per million of our own atmosphere.

This artist's impression shows the planet K2-18b, it's host star and an accompanying planet in this system.

This is the first time water has been detected in the atmosphere of a smaller-sized planet orbiting in its star's habitable zone, they report in the journal Nature Astronomy.

"Finding water in a potentially habitable world other than Earth is incredibly exciting", study author Angelos Tsiaras said in a statement.

"We don't really know what it's like down there".

The UCL team turned to Nasa's veteran Hubble space telescope, which observed K2-18b in the two years after its discovery.

Exoplanet science has literally opened new worlds to study, with planets populating the galaxy unlike anything in our small solar system. "This is not only because super-Earths like K2-18b are the most common planets in our Milky Way, but also because red dwarfs - stars smaller than our Sun - are the most common stars". None have been confirmed yet, however. It's quite close to its host star (with an orbital period of 33 days), but this star is half the size and temperature of the sun. Due to the crushing pressure, humans wouldn't be able to walk on the planet's surface; it would be more of a Cloud City situation, with pods floating in the gaseous atmosphere.

Kepler and Spitzer provide a broader range of observations (hence the arXiv paper's cloud formation models), but they're less precise than Hubble.

Scientists have detected water vapor in the atmosphere of K2-18 b, a potentially habitable alien world about twice the size of Earth. The Goldilocks zone is a range relative to a star where the temperature is not too hot and not too cold to support life.

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A research team used archival data collected by the Hubble Space Telescope between 2016 and 2017 that captured starlight as it passed through the atmosphere of the exoplanet.

They then modelled the atmosphere using three different approaches: cloudless, with water vapour in a hydrogen-helium atmosphere; cloudless, with water vapour, hydrogen-helium and molecular nitrogen; and cloudy, with water vapour and hydrogen-helium. Most have been detected using the transit method, where telescopes watch for a slight, fleeting dimming of a star's light as a planet passes in the field of view.

Professor Giovanna Tinetti (UCL CSED), co-author and Principal Investigator for ARIEL, said: "Our discovery makes K2-18 b one of the most interesting targets for future study". Its star is relatively inactive, and hasn't put out any flares since scientists started observing the system.

Now, a team of astronomers from the United Kingdom has announced the successful detection of water vapor in the exoplanet's atmosphere. Over time, the flow of charged particles and plasma from the sun stripped Mars' atmosphere away. "Over 4,000 exoplanets have been detected but we don't know much about their composition and nature".

The new research suggests that K2-18b has an atmosphere after all.

Astronomer Jonti Horner of the University of Southern Queensland said the discovery was the first step towards finding smaller Earth-like planets capable of supporting life. For now, there's no way to know what conditions on its surface are like.

Data from the planet have been available for several years, but the UCL team developed specialist software to re-examine the wavelengths of light, looking for signs of water. But he added that the apparent presence of water was promising for K2-18b's habitability.

This massive range stems from the fact that, with Hubble observations, researchers can only identify a water signature, the "fingerprint" observed using transit spectroscopy; they can't tell how much water is there, Giovanna Tinetti, a researcher on this study and a professor of astrophysics at UCL, said during a September 10 news conference.

The next generation of space telescopes, including the NASA/ESA/CSA James Webb Space Telescope and ESA's ARIEL mission, will be able to characterise atmospheres in more detail as they will carry more advanced instruments.

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