Water detected on an exoplanet located in its star’s habitable zone

Signs of water vapour have been located by scientists on exoplanet K2-18b, a major step forward in the search for extraterrestrial life.


By Natalia Dec | Wed, 23 Oct 2019


Photo courtesy of ESA Hubble, M. Kornmesser (Wikimedia Commons)

Ever since the dawn of the discovery of new planets in the 1990s, researchers and astronomers have been on the hunt, and made steady progress, towards finding planets located in habitable zones of their stars—in these zones, the more amicable conditions can lead to the formation of liquid water and growth of life.

Results from the Kepler satellite mission obtained information about close to 2/3 of the exoplanets we are aware of today and showed that 5 to 20% of Earths and Super-Earths are found in the habitable zone of their stars. Despite this, however, probing the atmospheric properties and conditions of those habitable zone planets has been found to be very difficult, with true results having been obtained only recently.

The M-type star is less massive and cooler than the Sun, but due to the exoplanet’s proximity to it, K2-18b receives a similar amount of energy from its star as does the Earth from the Sun.

A study conducted by Professor Björn Benneke of the Institute for Research on Exoplanets at the Université de Montréal, doctoral student Caroline Piaulet, and several other collaborators, reports that water vapour and perhaps even liquid water clouds have been detected in the atmosphere of K2-18b. K2-18b is about nine times larger than Earth, and has been found in the habitable zone of its star. The M-type star is less massive and cooler than the Sun, but due to the exoplanet’s proximity to it, K2-18b receives a similar amount of energy from its star as does the Earth from the Sun.

According to astronomers, the similarities between our Earth and exoplanet K2-18b, suggest that it may potentially possess a water cycle, therefore allowing water to condense into clouds, and eventually, for liquid rain to fall. The research put into this was made possible through combining eight transit observations, which occur at the moment an exoplanet passes in front of its star, taken by the Hubble Space Telescope.

The Université de Montréal is closely acquainted with the K2-18 system, located 111 light-years away. The existence of the K2-18b exoplanet was confirmed by Professor Benneke and his team in a 2016 study utilising data from the Spitzer Space Telescope. Furthermore, the mass and radius of K2-18b were determined and confirmed by Ryan Cloutier, former Université de Montréal and University of Toronto PhD student.

"This represents the biggest step yet taken towards our ultimate goal of finding life on other planets, of proving that we are not alone. 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," says Björn Benneke on this newest discovery.

Thanks to our observations and our climate model of this planet, we have shown that its water vapour can condense into liquid water.

Researchers are currently of the opinion that the thick, gaseous cover which envelops K2-18b most likely prevents our current understanding of ‘life’ as we know it from developing on the planet’s surface. Despite this, the current study has enabled scientists to show that even planets of relatively low mass, which are commonly more difficult to study, can still be researched through utilising the newest astronomical instruments, which continue improving. Through studying exoplanets which inhabit the habitable zones of their stars, and have met the requirements for liquid water to exist, researchers and astronomers, in general, are much closer to further establishing whether there exist other signs of life beyond our Solar System.

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