by Max Harvey
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| K2-18b (source: Wiki Commons) |
The search for life is something that has fascinated much of
the scientific community since space exploration began. Despite having begun
with the questioning of ‘Are we alone in this universe?’ the advancements in
modern technology have given rise to a platform from which scientists can now
scour the skies in search of lifeforms that have defied all odds by coming into
existence.
The very nature of life as we know it, however, demands an
extensive list of strict parameters to be met in order for there to be any
chance of success. This list can be simplified to include 3 things: a liquid
solvent, chemical building blocks and an energy source. Using Earth as an
example this equates to water, organic molecules and the sun. Despite the use
of another liquid solvent (e.g. liquid methane) being proposed as suitable to
support life, because water and carbon based life fuelled by stellar energy is
what we know most about, the search is narrowed to fit these prerequisites for
life.
Whilst there are many planets and exoplanets that have
sufficient access to stellar energy and a number of places upon which organic
molecules have been found, the search for this ever so vital source of water
has been somewhat more difficult.
Enter K2-18b, a planet twice the size of Earth that orbits
the red dwarf star K2-18 approximately 110 light years away. This newly found
planet orbits in what is known as the habitable zone for a red dwarf star,
meaning that it has the potential to support life as it has the correct amount
of sunlight reaching it and its temperature of roughly -8 degrees celsius is
potentially life sustaining.
However the crown in the jewel of this new discovery that
has led to the exoplanet K2-18b being dubbed as potentially the best place to
seek life beyond our solar system is the discovery of water. This discovery was
made by a team led by Björn Benneke and was achieved by the analysis of changes
of light as K2-18b passed in front of the Hubble telescope. The data showed
that the wavelength of light absorbed by water weakened when the exoplanet was
in the way. This led to the conclusion that K2-18b not only has an atmosphere
but that it contains water vapour too. Through further calculations this
concentration of water vapour in the atmosphere of K2-18b has been proposed to
be even as high as 20-50%!
The discovery of this water vapour in conjunction with the
plants positioning within the habitable zone makes a strong argument for the
notion that liquid water is present on the surface of the exoplanet and as discussed
above, the existence of a liquid solvent is a fundamental prerequisite if any
life is going to exist.
So why is this discovery of water vapour in the atmosphere
of K2-18b such a big deal? Despite our abundance of water on planet earth that
we take for granted most days as we wash our hands or take a bath, water is
very hard to find in the rest of the universe and with this discovery, K2-18b
is now the only planet known to us outside of our solar system that has an
atmosphere containing water vapour and resides within the habitable zone of its
star. As Angelos Tsiaras from UCL has said, ‘[this] makes it the best candidate
for habitability we know of’.
Despite the seemingly perfection of this exoplanet as a host
for life, a number of hurdles are still left to cross. While K2-18b most likely
does have a rocky core, the majority of the planet is likely to be gaseous.
This makes the exoplanet more comparable to Neptune than to Earth. In addition
to this, liquid water is yet to be confirmed to exist on the planet despite
there being evidence of gaseous water vapour in the atmosphere.
However, the discovery of K2-18b does show that planets
containing many of the prerequisites for life do exist outside of our solar
system and this lends promise to the future in which many more life supporting
exoplanets may be found. In particular the James Webb Space Telescope hoping to
be launched in March 2021 will enable a new level of analysis to occur of
exoplanets and will aid in the search for the ever elusive existence of life
other than our own.
Whether or not a planet such as K2-18b would even be
habitable is still up for debate and many argue that even if life did exist it
would be very different to our own. However what K2-18b has done is it has
overcome a huge milestone in the search for life and has installed an appetite
in the science community for the discovery of more exoplanets just like it.
Max Harvey
Sources: space.stockexchange.com
en.m.wikipedia.org
NewScientist
How to build a
habitable planet by C.H.Langmuir and W.Broecker
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