Is there alien life in our Solar System?
The search for life in our Solar System is the next big challenge for scientists, but where are the best places to look?
When we think about alien life in the Solar System, our first thought tends to be of our nearest neighbour of Mars. With its Earth-like past and the discovery of water on its surface, it proves to be a perfect candidate.
However our best chance for finding life in the Solar System may be much further afield.
Scientists are now turning their attention to the icy moons of Jupiter and Saturn where underground oceans and water jets may provide some of the basic building blocks for life as we know it.
What does life need?
Before scientists can begin to search for life in the Solar System, they first need to know what to look for.
So, what do we need for life as we know it to exist? As far as we know, life needs three basic things: liquid water, basic chemical elements like oxygen, and an energy source. With just these basic components, only basic life forms such as bacteria could exist. We see examples of this in the extremophiles that live deep under the ocean or near the hellish environment of volcanoes.
Therefore scientists are expecting that any life we find in the Solar System to be microbial rather than human-like. This means that we probably won’t be able to communicate with any life in our Solar System, but if we discover that life has developed elsewhere in our Solar System then that means that it could also form elsewhere in the universe, perhaps on a grand, complex scale.
Where to look for alien life?
The next big question is where should we be looking?
Here on Earth, where there is water, there is life, so it makes sense to look for liquid water elsewhere in the Solar System.
This is where the ‘icy moons’ of Jupiter and Saturn could be really promising places for alien life. Scientists have found strong evidence that these moons have oceans of liquid water beneath their icy surfaces.
Thanks to the Galileo mission in the mid-1990s and more recent Hubble Space Telescope observations, scientists believe that one of Jupiter’s moons, Europa, has an ocean of liquid water beneath its icy crust. This is because jets of liquid water have been observed on the surface of Europa.
This ocean, shielded by a layer of ice from the harsh radiation of Jupiter’s magnetic field, could host life lurking below, perhaps similar to the microbes that live near hydrothermal vents here on Earth.
Jets of liquid water were also observed on Saturn’s moons Enceladus during the Cassini mission. In 2008, the spacecraft flew through the plumes to discovered that they contained carbon dioxide, carbon monoxide and other organic molecules alongside the water vapour that had been observed.
It is therefore possible that these molecules may be present in the water vapour jets of Europa, which would provide further evidence of Europa’s habitability.
Another intriguing candidate is Saturn’s moon Titan, which was visited by the European Huygens probe in 2005. During its descent and landing on the surface of Titan, Huygens found that Titan also has an ocean hidden beneath its crust, as well as lakes of liquid methane and ethane on its surface.
These discoveries are important because methane and ethane contain the elements carbon and hydrogen which are some of the raw ingredients required for life. These discoveries make Titan a prime target for further exploration, and there have even been missions proposed to ‘sail’ the seas of Titan.
The European Space Agency is developing a new mission to explore the moons of Jupiter that could potentially harbour life called JUICE (JUpiter ICy moons Explorer). The targets for this mission are three of Jupiter’s largest moons: Europa, Ganymede, and Callisto.
Professor Emma Bunce from the University of Leicester will be leading on two of the scientific instruments on board the spacecraft. These instruments will be studying both the potential underground oceans and the atmospheres of the icy moons for any elements needed for life.
JUICE is set to launch in 2022 and will arrive at Jupiter in 2029 before beginning three years of observation of the icy moons.
NASA is also developing a mission to Jupiter’s moon Europa, called Europa Clipper, which will study, amongst other things, the thickness of Europa’s icy crust and the composition of the water plumes observed by the Hubble Space Telescope. Europa Clipper will be launching in the 2020s after receiving the go-ahead for the mission in August 2019.
About the author: Eleanor Morton is a physics student at the University of Leicester and works as a Science Interpreter at the National Space Centre.