The Search for 'Life' on Other Planets

by Max Harvey




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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