Astronomers have detected water vapor
on the exoplanet K2-18b -- a major discovery in the search of alien life.
Université de Montréal – September 11,
2019 -- Ever since the discovery of the first exoplanet in the 1990s,
astronomers have made steady progress towards finding and probing planets
located in the habitable zone of their stars, where conditions can lead to the
formation of liquid water and the proliferation of life.
Results from the Kepler satellite
mission, which discovered nearly 2/3 of all known exoplanets to date, indicate
that 5 to 20% of Earths and super-Earths are located in the habitable zone of
their stars. However, despite this abundance, probing the conditions and
atmospheric properties on any of these habitable zone planets is extremely
difficult and has remained elusive... until now.
A new study by Professor Björn Benneke
of the Institute for Research on Exoplanets at the Université de Montréal, his
doctoral student Caroline Piaulet and several of their collaborators reports
the detection of water vapour and perhaps even liquid water clouds in the
atmosphere of the planet K2-18b. This exoplanet is about nine times more
massive than our Earth and is found in the habitable zone of the star it
orbits. This M-type star is smaller and cooler than our Sun, but due to
K2-18b's close proximity to its star, the planet receives almost the same total
amount of energy from its star as our Earth receives from the Sun.
The similarities between the exoplanet
K2-18b and the Earth suggest to astronomers that the exoplanet may potentially
have a water cycle possibly allowing water to condense into clouds and liquid
water rain to fall. This detection was made possible by combining eight transit
observations -- the moment when an exoplanet passes in front of its star --
taken by the Hubble Space Telescope.
The Université de Montréal is no
stranger to the K2-18 system located 111 light years away. The existence of
K2-18b was first confirmed by Prof. Benneke and his team in a 2016 paper using
data from the Spitzer Space Telescope. The mass and radius of the planet were
then determined by former Université de Montréal and University of Toronto PhD
student Ryan Cloutier. These promising initial results encouraged the iREx team
to collect follow-up observations of the intriguing world."
Scientists currently believe that the
thick gaseous envelope of K2-18b likely prevents life as we know it from
existing on the planet's surface. However, the study shows that even these
planets of relatively low mass which are therefore more difficult to study can
be explored using astronomical instruments developed in recent years. By
studying these planets which are in the habitable zone of their star and have
the right conditions for liquid water, astronomers are one step closer to
directly detecting signs of life beyond our Solar System.
"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.
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