The Earth is dying. You probably already knew this. Our rampant use of fossil fuels and unsustainable energy resources has driven our planets climate to the brink of irreversibility, some experts say we only have a few decades to turn it around, some say it is a matter of years, and some even say it is only a matter of months. With estimates like this, I think it is clear we need a continuity plan for the future. Furthermore, a plethora of other natural disasters could be on their way; the Yellowstone super-volcano is due to erupt, it seems like every other week we see a news article saying another asteroid is heading towards Earth, and rising sea levels are causing mass flooding globally . Point being we need to think about an eventuality where Earth, simply, is not the future. So, where next?
First, we must consider some factors we need to look at which make a planet or moon a viable option to live on. Like when you are looking for accommodation before university starts, you do not want a place with leaks, you do not want one in a rough neighbourhood and you certainly do not want one in an asteroid path. The number one factor we need to consider is water, this is imperative as we are water-based life forms and require water to survive. Temperature is the next most important factor, if the temperature is incredibly volatile on the surface then we have an issue as humans can only really operate functionally in a relatively small temperature range. The third factor is the existence of an atmosphere or the viable option to make an atmosphere; this is very important as an atmosphere acts as a barrier of molecules which can protect the surface from asteroid impacts, furthermore, an atmosphere allows heat to be trapped on the surface which helps maintain a steady temperature.
3 Coming in at number 3, the famous moon of Jupiter, Europa. Europa meets our number one condition perfectly, there is significant evidence to suggest there is an abundance of water beneath the crust. This evidence comes from a detection of a strong magnetic field emanating from the moon which suggests there is a large amount of conductive fluid within it, such as salt water, a perfect environment for the potential growth of microbial life forms. On the other hand, Europa is lacking a very potent atmosphere, it is made completely of oxygen but in a very small quantity, meaning despite the abundance of water there is no chance of setting up mass agriculture without terraforming. The surface may be extremely flat which would be ideal for initial construction, however, the temperature is extremely cold due to the lack of atmosphere at around 110K at the equator . In the future this may change if we develop the tools to perform mild planetary terraforming ; if we find a way to melt the ice caps and unlock the water beneath the surface, its ocean can start to produce carbon dioxide which would build a thicker atmosphere while also providing another crucial ingredient for plant life in CO2. For this reason, I believe Europa has the potential to be a prime candidate for a place to live in the future but at a great cost and risk, so I will rate it a 5/10.
2 At number 2, we have another moon, this time of Saturn, its name being Titan. It is said to be the most planet-like moon that we know of due to its dense atmosphere. A fun fact about this moon is that it is actually larger than Mercury, if it were not orbiting Saturn and instead orbiting the sun, we would in fact call it a planet . Titan is known for its peculiar atmosphere; it is primarily composited of nitrogen (95%) and the rest is methane (4.9%) with other trace elements such as oxygen and CO2. This methane commonly condenses near the surface to form methane clouds which rain down similarly to the regular water rain we see here on Earth. Similarly to Europa, Titan gives off a noticeable magnetic signature which again is a sign that water exists below the surface which is another plus. Alas, we do not see much of that water on the surface as the surface is comprised mainly of hydrocarbons formed in the upper atmosphere by the reaction between methane and ultra-violet rays from the Sun. The surface temperature leaves a lot to be desired at 93K. For this reason, I cannot recommend anyone moves there right now, but in the future, this could be a very viable option. Titan would need a lot less work from our end to set up reasonable living conditions as it already has an atmosphere and the potential for access to water . A potential initial solution to the temperature problem is the evidence for the existence of hydrothermal vents near to the surface of Titan, the temperature around these could be manageable, while also having an access point to deeper in the crust of this moon could be imperative for drawing heat to the surface to help sustain life. For these reasons I give Titan a 7/10.
Before we come to the finale, there are some honourable mentions. The Moon is a great option for its locality to Earth and the fact we already have so much knowledge about it, its downsides are that it has no atmosphere and some, but very little water that we know of. Venus surprisingly makes this list, this is because we would not actually consider living on its surface, that would be impossible due to the inhospitable temperatures and pressures, but above the clouds by about 30 miles it is not as bad, at a cosy 70oC . Enceladus is another potential option, another moon of Saturn, with water being detected by a mission run by none other than our very own, Professor Michele Dougherty (Imperial College London). Its only issue being that the moon is tiny, being only 500km across it is about the size of Arizona.
1 Some of you may have guessed the number one pick for the best place to live in the solar system (besides Earth of course), and that would be Mars. The little red planet is a lot more like Earth than we give it credit for, there is strong evidence that it had and still has water given the large features known as recurring slope lineae (RSL), these are long winding streaks of dirt which appear to have been carved out by the flow of water on its surface. Many believe there used to be water on its surface but after its atmosphere evaporated the water vapour went with it. However, recent evidence shows there is ice stored below the surface so there is hope that the oceans that once covered the surface are now dormant, but accessible by us, below it . Moreover, distance from here to Mars is a big positive, it being our neighbouring planet means we can transport materials and people back and forth almost yearly. Whereas to travel to a lot of these other options you would have to wait many years, sometimes decades due to the very long orbital periods of Saturn / Jupiter. The issue with Mars is that it lost its atmosphere around 4.2 billion years ago due to a lack of a magnetic field, which is another issue in of itself as a magnetosphere is very useful in protecting the surface from the radiation produced by the Sun. However, for the time being, there can be measures taken to overcome these problems: due to the distance being relatively short for stellar travel, we could sustain a small colony using only supplies from Earth for a very long time, providing them with oxygen, food to grow internally, and materials to continue research and construction. Overall Mars is most likely our next frontier in space travel and will likely one day become our second home. Given Elon Musk is trying to get there as soon as possible, and NASA have revealed plans to also start aiming rockets in that direction, I give Mars a 9/10.
Despite this comparison seeming meaningless, as Mars is the obvious choice for the next big move, this research into other possibilities could be very useful for us to understand where we came from and where we could be going. Even if it turns out we cannot ever go to Europa due to the temperature, we could still find microscopic evidence of life there which would be an extraordinary breakthrough in our history. We could find huge deposits of rare-Earth minerals which help us build up our colonies on whatever new home we choose. Most importantly, we do this because we are curious, we do it because we are human.
 McGrath M. Climate change: 12 years to save the planet? Make that 18 months [Internet]. BBC News. 2021 [cited 20 February 2021]. Available from: https://www.bbc.co.uk/news/science-environment-48964736
 Ingredients for Life? | Europa – NASA’s Europa Clipper [Internet]. NASA’s Europa Clipper. 2021 [cited 20 February 2021]. Available from: https://europa.nasa.gov/europa/life-ingredients
 The Definitive Guide To Terraforming – Universe Today [Internet]. Universe Today. 2021 [cited 20 February 2021]. Available from: https://www.universetoday.com/127311/guide-to-terraforming/
 Titan (Moon) Facts [Internet]. Space Facts. 2021 [cited 20 February 2021]. Available from: https://space-facts.com/moons/titan
 Titan – In Depth [Internet]. NASA Solar System Exploration. 2021 [cited 20 February 2021]. Available from: https://solarsystem.nasa.gov/moons/saturn-moons/titan/in-depth/
 S. Powell C. NASA has a plan to let humans soar above the clouds on Venus [Internet]. NBC News. 2021 [cited 20 February 2021]. Available from: https://www.nbcnews.com/mach/science/nasa-has-plan-let-humans-soar-above-clouds-venus-ncna879851
 Tyler Redd N. Water on Mars: Exploration & Evidence [Internet]. Space.com. 2021 [cited 20 February 2021]. Available from: https://www.space.com/17048-water-on-mars.html
Image 1: NASA/JPL-Caltech/SETI Institute
Image 2: NASA/JPL/Space Science Institute
Image 3: Lick Observatory/ESA/Hubble
Image 4: NASA/JPL-Caltech