Abstract

With the advancement of technology and scientific understandings, humans have been able to investigate many different astronomical bodies in outer space. In this review report, I explore some of the many worlds of our solar system in which humans could potentially colonise in future. It was Professor Michelle Dougherty, from the Imperial College London, who inspired me to research this topic. I had the pleasure to listen to one of her lectures during which she was talking about her involvement in the Cassini space mission to explore Enceladus, also studied in this work. The focus of my research was looking at astronomical bodies before, and after the so-called snowline, a concept introduced to me by Professor Dougherty. My work aims to scrupulously analyse the most appropriate celestial body in our solar system to colonise by using four ‘must be’ factors – water, atmosphere, magnetic field and a specific range of temperature. I accomplished my aim via reading various articles as well as watching documentaries to help consolidate my findings. After investigating each celestial body in detail, my analysis revealed that Europa is the best body to colonise as it meets the requirements needed for humans to survive on another astronomical body. Despite its temperature, the remaining factors, water content, atmosphere and magnetic field on Europa, made it convincing enough for it to be the next destination in which we call home.

 

Introduction

The Earth provides many essentials such as food, water, and shelter, which keep us alive, but what essential resources allow us to survive? A perfect range of temperature, presence of water and an atmosphere are the three survival factors that the Earth possesses, which allow humans to live on it.

Water is one of the most crucial factors that humans require to live on Earth. Water reservoirs like oceans, lakes and rivers are home to many life forms. They cover 71% of the surface of Earth [1]. Throughout decades of research, there have been many discoveries of astronomical bodies that have sources of water, leading to further investigations of whether we can live beyond this planet.

Aside from water, other features necessary for human survival include a temperature approximately between 258K and 388K. The ideal temperature for us to live on the Earth is around 288K (14.85 degrees Celsius) [2].

The next significant feature is having an atmosphere. Our atmosphere consists mainly of nitrogen, oxygen and other gases (78%, 21% and 1% respectively) [3]. The other gases include argon, carbon dioxide, methane, water vapour and neon. The gaseous form of water corresponds to only 0.01% of the atmosphere [4]. The atmosphere plays a vital role as a form of protection against harmful radiation (Fig.1). It also protects our planet from astronomical bodies such as meteoroids that pose a danger to human life. It also partakes in a natural process that keeps our world at an adequate temperature (Fig.2).

Figure 1. Absorption of electromagnetic radiation by the atmosphere. Gamma rays, x-rays, ultraviolet and radio waves are displayed to be 100% absorbed by our atmosphere. Ultraviolet radiation from the sun, if not absorbed by our atmosphere, can be extremely harmful. Hence, we need an atmosphere. [A]

 

 

Figure 2. Energy budget of the Earth. The amount of solar energy absorbed by the atmosphere of the Earth is displayed. This system assists in keeping the Earth warm by reflecting, absorbing and transmitting solar energy from the Sun. [B]

My research will take you on a journey, exploring potentially habitable bodies within our solar system. You will be able to see comparisons of planets before and beyond the snowline, the boundary of where simple molecules freeze. The idea of the snowline was introduced to me by Professor Michelle Dougherty from Imperial College. Fig.3 displays the location of the snowline in our solar system. As this is one of the approaches to investigate the possibility of life on other celestial bodies, I instantly found it engaging as colonising planets with regards to the snowline is rarely spoken about. Mercury, Venus, Earth and Mercury are before the snowline while Jupiter, Saturn, Uranus and the dwarf planet Pluto are beyond the snowline. The snowline is significantly vital since particles, like water molecules, freeze beyond it [5]. As the bodies located after the snowline are much further away from the Sun, the intensity of radiation emitted from the Sun to the bodies is significantly lower. Therefore, the bodies are extremely cold. It would be natural to assume that life is possible only before the snowline. However, my report highlights that this may not be the case.

 

Figure 3. Location of the snowline. A vertical line is displayed between Mars and Jupiter conveying that Mercury, Venus, the Earth and Mars are located before the snowline and Jupiter, Saturn, Uranus and Neptune are located after the snowline. The bodies located after the snowline are much colder [C].

Having the correct temperature and atmosphere, a source of water and magnetic field make celestial bodies potential candidates for habitable places for human colonisation. The next chapter carries detailed discussions of these conditions in different astronomical bodies before and beyond the snowline, summarised in Fig.4 and Fig.5. 

Factor Planet	Average Temperature (K)		Atmosphere	Water source
	Daytime	Night-time
Ceres	200	130	✔	✔
Mars	293	200	✔	✔
Venus	744		✔	X
The Moon	373	100	X	✔

Figure 4. Possession to the factors of the astronomical bodies before the snowline. Ticks display that the body possesses the factor. Crosses display the body does not possess the factor. [D]

Factor Planet	Average Temperature (K)	Atmosphere	Water source
Enceladus	72	✔	✔
Europa	113	✔	✔
Titan	94	✔	✔
Pluto	40	✔	✔

Figure 5. Possession to the factors of the astronomical bodies after the snowline. Ticks display that the body possesses the factor. Crosses display the body does not possess the factor. [E]

 

For astronomical bodies before the snowline, I focused on Ceres, Venus, Mars and the Moon (Fig.6 A-D). Titan, Enceladus, Europa and Pluto were my chosen bodies to focus on for after the snowline (Fig.6 E-H). My choice of these bodies was influenced by the information I attained from attending a university lecture based on this topic. I also briefly researched into several astronomical bodies to gain some more knowledge before narrowing down my options to these eight celestial bodies.

 

Figure 6. Astronomical bodies before (A-D) and beyond (E-H) the snowline.

A) Ceres, a dwarf planet located in an asteroid belt between Mars and Jupiter [E].

B) Venus, the second closest planet to the Sun [F].

C) Mars, the fourth closest planet to the Sun [G].

D) The Moon, the only Moon of the Earth [H].

E) Titan, the Moon of Saturn [I].

F) Enceladus, the sixth-largest Moon of Saturn [J].

G) Europa from the 79 moons of Jupiter [K].

H) An image of the Northern hemisphere of Pluto [L].

 

 

Discussion

Temperature

The temperature of the astronomical bodies is the first factor I will discuss here. This section will explore the various temperatures of my chosen celestial bodies and whether they are habitable for humans.

Before the snowline

A shorter distance between the Sun and an astronomical body means it receives more radiation which then turns into heat on the surface of this body. Venus has a consistent temperature of around 744K due to its relatively short distance to the Sun [6]. It is much closer than the Moon, Mars and Ceres as you can see in Fig. 7. Such high temperature makes it near impossible to colonise Venus. It could be possible to create shelters made of materials such as tantalum carbide which withstands temperatures up to 4273K [7]. However, this would be extremely difficult to do as it may not be economically or practically feasible to transport large amounts of the material required to build the shelters in a safe manner.

Planets	Earth	Ceres	Mars	Venus	Moon
Average distance from the Sun (km)	150,000,000 [8]	413,000,000 [9]	228,000,000 [10]	108,000,000 [11]	150,000,000 [12]

Figure 7. Distance between the Sun and the astronomical bodies before the snowline. The Earth added for comparison. [M]

Temperatures on the Moon, whilst not as hot as on Venus, can range from 373K during the day to 100K at night [13]. There have been multiple exploration missions to the Moon. The Apollo 11 mission was the first successful landing of humanity onto the Moon [14]. This mission brought an enormous step forward into future space exploration. It was due to the application and testing of many equipment such as spacesuits, which have insulating material with a reflective outer layer, or cooling and heating systems that allowed us to survive the extreme temperatures of the Moon [15]. Our knowledge and understanding of the Moon makes it relatively easier to inhabit compared to other bodies.

Considering accomplished missions to the Moon, withstanding the temperatures on Mars would be much easier. This is because Mars has a similar temperature near the equator during the day to the average surface temperature of the Earth as opposed to the Moon. It reaches 293K near the equator [16, 17] meaning humans could survive near the equator of Mars as a temperature of 293K is a typical summer day in England.  On the other hand, temperatures near the poles and at night on Mars and the Moon would then require appropriate measures to be taken so that humans can survive in these cold temperatures. 

Ceres would also require similar measures to the night-time conditions as its surface temperature ranges from 130K to 200K [18, 19]. These cold conditions are similar to the night-time conditions of the Moon. Luckily, wearing a new spacesuit from NASA, withstanding up to 116K [20], could be efficient enough in these temperatures. On astronomical bodies that experience these icy conditions, a spacesuit can be worn. However, a spacesuit is no longer considered practical when the oxygen supply runs out as the astronaut would not be able to breathe.

Based on my comparison, Mars has the most suitable temperature, hence making it an excellent astronomical body to colonise. Humans could colonise near the equator of Mars, where the surface temperature during the daytime is around 293K [21] which is a temperature that we know we can survive under.

After the snowline

It is reasonable to assume that due to the far distance of the astronomical bodies after the snowline from the Sun, (Fig.8) their surface temperatures will be even more extreme. Fig.5 presents the range of these temperatures ranging from 47K on Pluto [22] to 113K on Europa [23]. It would be unrealistic for humans to survive in these temperatures unless a spacesuit and space capsules are made that can assist us in overcoming these inhabitable (for the time being) conditions.

Planets	Earth	Enceladus	Europa	Titan	Pluto
Average distance away from the Sun (km)	150,000,000 [8]	1,400,000,000 [24]	780,000,000 [23]	1,400,000,000 [25]	5,900,000,000 [26]

Figure 8. Distance between the Sun and the astronomical bodies after the snowline. The Earth added for comparison. [N]

Out of all the bodies located after the snowline, Europa has the warmest surface temperature, hence it would be better to attempt to colonise it before the others. As discussed above, the newest space suit can withstand 116K [27], which is only a few Kelvin above the highest temperature recorded on Europa. With developing this technology, hopefully, humans could visit Europa in the future.

In terms of surface temperature, evidently, Mars with its 293K [16, 17] near its equator, is the most habitable planet out of all the astronomical bodies, both before and after the snowline. The planets beyond the snowline are too cold to inhabit and would require advanced equipment and technology for humans to be able to withstand these conditions.

Atmosphere

The atmospheres of the astronomical bodies consist of many different molecules and elements that are different from the ones of the Earth. An ideal body would be composed of mainly nitrogen and oxygen with a small percentage of carbon dioxide, methane, water vapour and neon. However, we could potentially live in different conditions so long as the chemicals that make up the atmosphere are not harmful to humans – for example, a high concentration of carbon monoxide. In this section, the composition of each of the atmospheres will be discussed.

Before the snowline

Ceres, Mars and Venus have atmospheres, but their compositions are significantly different from the one on our planet (Fig. 9).

Ceres	Mars	Venus	The Moon
Water Vapour	Carbon Dioxide (95.32%) Nitrogen (2.7%) Argon (1.6%) Oxygen (0.13%) Carbon Monoxide (0.08%) Minor amounts of: Water Nitrogen Oxide Neon Hydrogen-DeuteriumOxygen Krypton Xenon	Carbon Dioxide (96%) Nitrogen (3.5%) Minor amounts of: Argon Sulfur Dioxide Water Vapour Carbon Monoxide	Helium Argon Neon Ammonia Methane Carbon Dioxide Potassium Sodium

Figure 9. Composition of the atmospheres of the astronomical bodies before the snowline [O,28].

The Moon has a so-called lunar atmosphere, which is not considered to be an authentic atmosphere due to too small amounts of molecules in it. The number of molecules is so small – on Earth we would think it to be a vacuum [29]. Our atmosphere lacks the unusual gases such as sodium and potassium, however, these gases are present in the Moon’s atmosphere leading us to wonder where these elements came from. The composition of the atmosphere of the moon is displayed in Fig.9. [30]

Relative to the atmosphere of the Earth, Ceres has a fragile atmosphere which is only sometimes present because the energy from the Sun randomly heats exposed ice particles, causing them to sublime, forming a thin layer of water vapour atmosphere which lasts for a very short period of time[31]. Due to the inconsistent nature of the atmospheres of Ceres and the Moon, they would not be an acceptable form of protection against dangers coming from outer space. Some dangers include being hit by objects travelling at high speeds or harmful radiation that is emitted from bodies close by entering into the atmosphere of Ceres and the Moon. It also explains the cold temperatures at their surfaces as heat is not kept within the atmosphere, making it very difficult for humans to consider living there. 

Mars and Venus, however, are both known to have more densely filled atmospheres in comparison to the Moon and Ceres. Primarily made up of carbon dioxide with very little oxygen and nitrogen, is the atmosphere of Mars, and it is relatively 100 times thinner than the one on the Earth [32]. According to recent studies, the atmosphere of Mars was thick in the past, but it has been thinned over years due to intense pressures of powerful solar winds [32]. Solar winds are streams of charged particles, typically electrons and protons, that are emitted from the Sun. Due to its thin atmosphere, water was unable to be kept within it as the vapour quickly escaped into outer space. It cannot trap heat in either, creating a cold planet for us to live on in certain areas on Mars as well as making us liable to danger. To overcome this, the process of terraforming Mars would be a solution. Terraforming Mars would involve the introduction of structures such as factories that produce our power and energy supplies, which then in turn produce greenhouse gases. For example, electricity is produced in factories by burning fossil fuels and biological materials resulting in the emission of greenhouse gases such as carbon dioxide. As the amount of greenhouse gases increases, the atmosphere can gradually build up and more of these gases can absorb radiation from the Sun recreating the greenhouse effect.

Venus has a crushing atmosphere relative to the Moon, Ceres and Mars. 96% of the atmosphere is carbon dioxide, 3.5% nitrogen and less than 1% includes carbon monoxide, argon, sulphur dioxide and water vapour [33]. Carbon dioxide is thought to be a pollutant on the Earth and has adverse health effects. Exposure to high levels of carbon dioxide can cause difficulty breathing, increased heart rate, elevated blood pressure and other symptoms. Hence, it can be detrimental to one’s physical health

With these astronomical bodies lacking a supply of sufficient oxygen in their atmospheres, humans would have to come up with a way of having a constant supply of it. We would have to transport large volumes of this gas from the Earth or find methods to produce it from available sources on them. Out of the discussed bodies, the Moon would be best to colonise by humans despite none of the astronomical bodies complying with the thickness and composition of the atmosphere on the Earth. Humans could live without an atmosphere on the Moon, but it would require a spacesuit as a form of protection against radiation. Nevertheless, scientists would have to consider other forms of protection to implement too. Even though Ceres has a thin atmosphere filled with ice, this is the most convincing body to be habitable with regards to its atmosphere. Ice is not a dangerous substance, so we would not have to worry about surviving under its roof and additionally, it could potentially act as a source of water and oxygen. 

After the snowline

In contrast to the bodies discussed in the previous paragraph, the one after the snowline, Enceladus, Titan, Pluto and Europa, all have stable and dense atmospheres (Fig.10).

Enceladus	Europa	Titan	Pluto
Water Vapour (91%) Nitrogen (4%) Carbon Dioxide (3.2%) Methane (1.7%)	Oxygen	Nitrogen (96%) Methane (3.5%) Hydrogen (0.5%)	Nitrogen (97%) Methane (2.5%) Carbon Monoxide (0.5%)

Figure 10. Composition of the atmospheres of the astronomical bodies after the snowline [P,28, 34].

Enceladus, one of the many moons of Saturn, was considered to be just like many of the countless objects in our solar system – cold, small and well outside the habitable zone. Nevertheless, due to the Cassini space mission, it is now one of the most consequential objects in our solar system. Initially, scientists thought of Enceladus to have an atmosphere suggested by the magnetometer of Cassini from images of their first flyby [35]. During their second flyby, their cameras obtained detailed photos of the south polar region of Enceladus. Their findings included the magnetic field of Saturn oscillating due to ionised water particles surrounding Enceladus [36]. The atmosphere of Enceladus is denser at the South Polar Region, which is the location of the water jets. The atmosphere consists of water vapour (91%) but also shows signs of minor components like molecular nitrogen (4%) and carbon dioxide (3.2%). There has also been evidence of simple hydrocarbons, which take the form of methane (1.7%) as well as trace amounts of propane, acetylene and formaldehyde [36]. +

On the other side of the spectrum lies Titan, which is known to have a dense nitrogen-rich atmosphere, with no oxygen available, meaning we would have to find a way to get a sufficient supply of oxygen. Even though the pressure on Titan is 60 % greater than the pressure on the Earth [37], humans would still be required to wear spacesuits to support them with oxygen. 

Pluto has an atmosphere like Titan, mostly made of nitrogen with carbon monoxide and methane present in smaller amounts [38]

Unlike any of the atmospheres above, Europa has a tenuous atmosphere made of oxygen [39]. The difference between the Earth and Europa is that the oxygen on Europa does not originate from its body as it does on the Earth. It is, instead, formed through a process called radiolysis [40]. Radiolysis is the dissociation of molecules by ionising radiation. In this case, ultraviolet radiation from the Jovian magnetosphere (the magnetosphere of Jupiter) collides with the icy surface, splitting water into oxygen and hydrogen.

Out of all my chosen astronomical bodies, the most habitable one would be Europa, purely because it possesses oxygen. Although Ceres could be the best to colonise before the snowline, its lack of oxygen puts it at a disadvantage in comparison to Europa.

Water Source

Having a water source is the main resource scientists look for at potential candidates for colonisation. In this section, I will discuss more details about the access to water in the astronomical bodies.

Before the snowline

The most significant feature that makes Ceres very similar to Earth is its water content.  Ceres is composed of approximately 25% water [41] because patches of sodium carbonate formed during water evaporation are observed around the planet [42]. Studies of Ceres revealed that patches of ice are gradually expanding suggesting that water, or water vapour, is made or is already present below the surface of Ceres, condensing underneath its surface [43, 44]. 

Mars has had a water source in the past according to evidence collected by two landing rovers on this planet, Fig.11. There are multiple pieces of evidence for the water source [45], including:

1. Gullies, a landform form created due to water
2. Formation of a mineral called gypsum made with water [46]
3. Liquid salty water located on steep slopes
4. Frozen layers of ice beneath the surface
5. A subsurface lake among pockets of ice

Figure 11. History of water content on Mars. The numbers below correspond to the billions of years ago. The blue patches on each planet represent the water present [Q].

Water ice was also found on the Moon in 2018 [47], which conveys that either the Moon is still active or water was always present there. Water ice can be a form of frozen salty water or frozen pure water. More research and evidence are needed to confirm the origin of water on the Moon. The Moon and Ceres both convey signs of water activity, making them more compelling to inhabit as opposed to Mars.

Venus, on the other hand, is the only planet that shows no signs of water on its surface. However, astronomers have detected that the atmosphere of Venus consists of 0.002% water vapour [48]. The reason for such a trace amount of water vapor can be explained with the fact that Venus is too close to the Sun. Hence, if there were to be any water present, it would all evaporate as the water boils at 373K which is much lower than the surface temperature of Venus. The small percentage of vapour found could be a piece of evidence of water present in the past.

Out of the chosen astronomical bodies, Ceres seems to be most habitable based on its water source as its evidence of ice patches expanding is the most compelling. Through more research and evidence of hidden widen water on these bodies, Mars could be the second-best candidate.

After the snowline

To find water sources on astronomical bodies beyond the snowline is hugely fascinating as temperatures are so cold that water would be frozen and difficult to find, but this is not the case. My findings reveal that these celestial bodies contain water.

During the second flyby of the Cassini spacecraft, cameras obtained detailed images of the south polar region of Enceladus. They discovered that geyser-like jets spewed water vapour and ice particles from an underground ocean in the south polar region of this Moon beneath its icy crust as shown in Fig.12 [49], which was a feature that was lacking in most other bodies scientists had discovered before. Additionally, scientists detected internal heat from this Moon suggesting it is still active.

Their final discovery was that along with other molecules like carbon dioxide, methane and ammonia, the jets of water contained large amounts of hydrogen, suggesting that Enceladus was undergoing a continuous hydrothermal process. This chemistry is very similar to the one created by hydrothermal vents in the oceans of the Earth [50] and can be used as an energy source by life if it happened to exist in the sea of Enceladus. It has given scientists a promising lead for Enceladus to become habitant in future. [51]

Figure 12. Structure of Enceladus displaying water jets being emitted from the South Pole and ocean layers. The thickness is not to scale [R].

Further discoveries from Cassini have concluded that on the surface of Titan (the largest moon of Saturn) are present lakes and seas made of liquid methane, and ethane, along with volcanic activity where liquid water lava is released [52]. On the Earth, this water system is replicated, where water fills lakes and rivers. Titan is the only other world we know that has liquid on its surface. This discovery could lead to further research on whether there is more water in these rivers. The most astonishing finding is the hidden underground ocean of liquid water, around 35 – 50 miles underneath its icy surface. Titan is a very realistic planet to live on because the source of water has been discovered [53].

Like Titan, Europa is habitable because it has an underground ocean underneath its icy surface, estimated to be 60 to 150 kilometres deep [54]. Detection of water suggests plumes shooting about 160km out of the surface. NASA has explained that the ocean can be projected onto the body for easy access as the ice shell in this Moon could touch the ocean. The ice cover allows the less dense ice to arise onto the surface, and this would be carrying samples of the ocean [54]. In this case, the ocean could be released onto the surface. Enceladus and Europa seem to be more habitable than Titan due to their underground oceans.

The last in my discussion is Pluto with its rocky core surrounded by a mantle of water ice. Some scientists propose the idea that it has a buried ocean underneath its icy surface and that layers of gas prevent it from freezing to a solid [55]. It is proven that the surface of the body has mountains made of blocks of water ice as tall as 2 to 3 kilometres, in which frozen gases like methane coat them [55]. We could somehow exploit the nature of its surface and extract water from the mountains as well as separate other chemicals possibly mixed with it. This would, however, be a complicated process to undergo and would require decades of planning and research.

From the evidence above, Enceladus is the most habitable since it is showing signs of the current activity of the water jets, perhaps providing a constant supply of water. Despite Titan and Europa having underground oceans, it would require much more research to confirm these findings. In addition to this, water sources found on Pluto have a lot of uncertainty and need more missions and research to confirm a suitable water source strongly.

Both Enceladus and Ceres display signs of current water activity, but due to ease of exploration and distance from Earth, Ceres would be more convincing to colonise out of all astronomical bodies.

Conclusion

By taking the aforementioned factors into consideration which were temperature, the composition of the atmosphere and the availability of water, Europa seems to be the best destination to colonise Fig.13.

Figure 13. Icy surface of Europa, with Jupiter in the background [S]

Despite its surface temperature of up to 113K, it is possible to live in spacesuits which would help to overcome these cold temperatures. On the other hand, a far distance from the Sun means less sunlight and long distance to travel.

Out of all researched bodies, abundant oxygen is present only in the atmosphere of Europa. In contrast, the atmosphere of Europa is thin but it is the only body after the snowline which contains oxygen, an essential element that allows us to breathe.

The most influential factor to colonise Europa is its source of water displayed in Fig.14. Plumes of water vapour shooting out of its surface convey it is an active body just like the Earth.

Figure 14. The Internal structure of Europa. A water ocean is found under an icy crust [T]

Europa and Enceladus are the only bodies which meet the requirements presented in Fig.4 and Fig.5, with Europa being much warmer than Enceladus. 

With regards to celestial bodies before the snowline, the best body to colonise would be Mars. The most convincing factor is its temperature. It is more plausible to live under a temperature of 293K as opposed to Europas temperature of 193K as it is warmer.

Another convincing factor is that the distance from Mars to Earth is much less than the distance from Europa to Earth, making it easier to transport goods and equipment and to travel to. As well as this, the greater distance of Europa makes it harder for scientists to study the body efficiently.

Despite the numerous amounts of evidence of water present on Mars, the water content is portrayed to be decreasing throughout the years, resulting in an unreliable source of water. Whereas on Europa, there is a large source of water which would require further studies of how to extract this water and purify it.

Finally, in terms of atmosphere, Europa’s atmosphere would be more suitable since it is primarily made of oxygen as opposed to such a small volume of oxygen present in the atmosphere of Mars.

My findings are based on factual data. Therefore, as part of scientific research, my report can be utilised by people wanting to research the human colonisation of astronomical bodies within our solar system. However, this report has limitations as it does not explore all possible places for human colonisation in our solar system. Also, it doesn’t explore all the human survival factors that would be taken into consideration by scientists which is why the conclusion is imprecise. To improve this research the next step will be to include other factors such as having a magnetic field, internal energy sources, access to nutrients, gravity, equipment needed to travel to bodies located far away and much more to make this analysis more accurate. 

Acknowledgments

Thanks to Dr M. Chikvaidze and Dr A. Dusza for their support and encouragement on my EPQ journey.

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[20] The Economic Times. “NASA Spacesuit: NASA’S New Spacesuit Can Withstand Over 120°C, Removes Toxic Gases And Regulates Temperature.” Economictimes.Indiatimes. 2019. Accessed Aug 23, 2020. https://economictimes.indiatimes.com/magazines/panache/nasas-new-spacesuit-can-withstand-over-120c-removes-toxic-gases-and-regulates-temperature/articleshow/71681239.cms.

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[22] NASA. “In Depth | Pluto”. NASA Solar System Exploration. 2019. Accessed Aug 23, 2020. https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth/

[23] Howell, Elizabeth. “Europa: Facts About Jupiter\’s Icy Moon And Its Ocean.” Space.com. 2018. Accessed Aug 23, 2020. https://www.space.com/15498-europa-sdcmp.html#:~:text=It%20is%20the%20smallest%20of,F%20(minus%20220%20C).

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[25] NASA. “Titan – In Depth.” NASA Solar System Exploration. 2019. Accessed Aug 22, 2020. [https://solarsystem.nasa.gov/moons/saturn-moons/titan/in-depth/.

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[28] Compound Interest. “The Atmospheres Of The Solar System.” CompoundChem. 2014. Accessed Aug 25, 2020. https://www.compoundchem.com/2014/07/25/planetatmospheres/.

[29] Dictionary. “Definition Of Vacuum.” Dictionary.Com. n.d. Accessed Aug 16, 2020. https://www.dictionary.com/browse/vacuum.

[30] NASA. “Is There An Atmosphere On The Moon?” NASA. 2013. Accessed Aug 13, 2020. https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html.

[31] NASA. “In Depth | Ceres – NASA Solar System Exploration.” NASA Solar System Exploration. 2019. Accessed Aug 16, 2020. https://solarsystem.nasa.gov/planets/dwarf-planets/ceres/in-depth/#:~:text=Atmosphere-,Atmosphere,transforming%20from%20solid%20to%20gas).

[32] Sharp, Tim. Mars\’ Atmosphere: Composition, Climate & Weather. Space.com. 2017. Accessed Aug 12, 2020.https://www.space.com/16903-mars-atmosphere-climate-weather.html#:~:text=The%20atmosphere%20of%20Mars%20is,is%2095%20percent%20carbon%20dioxide.&text=Carbon%20dioxide%3A%2095.32%20percent,Argon%3A%201.6%20percent.

[33] Redd, Nola Taylor. “Venus\’ Atmosphere: Composition, Climate And Weather.” Space.com. 2018. Accessed Aug 16, 2020. https://www.space.com/18527-venus-atmosphere.html#:~:text=Atmospheric%20makeup,and%20clouds%20of%20sulfuric%20acid.

[34] Universe Today. “Saturn\’s Icy Moon Enceladus.” Universe Today. n.d. Accessed Aug 18,2020. https://www.universetoday.com/48796/enceladus/.

[35] NASA. “Cassini Finds An Atmosphere On Saturn\’s Moon Enceladus.” NASA Solar System Exploration. 2005. Accessed Aug 17, 2020. https://solarsystem.nasa.gov/news/12323/cassini-finds-an-atmosphere-on-saturns-moon-enceladus/.

[36] Thompson, Jay R. ”The Moon With The Plume.” NASA Solar System Exploration. 2017. Accessed Aug 27, 2020. https://solarsystem.nasa.gov/news/13020/the-moon-with-the-plume/.

[37] NASA. “Titan – In Depth.” Solar System Exploration. 2019. Accessed Aug 19, 2020. https://solarsystem.nasa.gov/moons/saturn-moons/titan/in-depth/.

[38] Redd, Nola Taylor. “Does Pluto Have An Atmosphere?” Space.com. 2016. Accessed Aug 19, 2020.

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[39] NASA. “Europa.” NASA Solar System Exploration. 2019. Accessed Aug 19, 2020. https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth/.

[40] Phys.org. “Jupiter\’s Moon Europa.” Phys.org. 2015. Accessed Aug 19 2020. https://phys.org/news/2015-09-jupiter-moon-europa.html.

[41] NASA. “In Depth | Ceres” NASA Solar System Exploration. 2019. Accessed Aug 7 2020. https://solarsystem.nasa.gov/planets/dwarf-planets/ceres/in-depth/.

[42] Maynard, James. “Dwarf Planet Ceres Is Covered In Deep Salty Oceans, Spacecraft Finds.” Thenextweb. 2020. Accessed Aug 22, 2020. https://thenextweb.com/syndication/2020/08/19/dwarf-planet-ceres-is-covered-in-salty-and-deep-oceans-dawn-spacecraft-finds/.

[43] Griffin, Andrew. “Nasa Reveals Findings From Journey To Mysterious World In Asteroid Belt.” The Independent. 2020. Accessed Aug 19, 2020. https://www.independent.co.uk/life-style/gadgets-and-tech/news/nasa-ceres-dawn-spacecraft-dwarf-planet-solar-system-a9663451.html.

[44] Liverpool, Layal. “Dwarf Planet Ceres May Be Home To An Underground Ocean.” New Scientist. 2020. Accessed Aug 19, 2020. https://www.newscientist.com/article/2251403-dwarf-planet-ceres-may-be-home-to-an-underground-ocean/.

[45] Redd, Nola Taylor. “Water On Mars: Exploration & Evidence.” Space.com. 2018. Accessed Aug 9, 2020. https://www.space.com/17048-water-on-mars.html.

[46] Grant, Bonnie L. “What Is Gypsum: Using Gypsum For Garden Tilth.” Gardening Know How. 2020. Accessed Aug 9, 2020. https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/using-gypsum-in-garden.htm.

[47] Wall, Mike. “Water Ice Confirmed On The Surface Of The Moon For The 1St Time!” Space.com. 2018. Accessed Aug 23, 2020. https://www.space.com/41554-water-ice-moon-surface-confirmed.html.

[48] Universe Today. “Is There Water On Venus?” Universe Today. n.d. Accessed Aug 19, 2020. https://www.universetoday.com/36291/is-there-water-on-venus/#:~:text=Well%2C%20there%20isn%27t%20any,t%20be%20on%20the%20surface.&text=Astronomers%20have%20detected%20that%20the,consists%20of%200.002%25%20water%20vapor.

[49] NASA. “Enceladus | Science.” NASA Solar System Exploration. 2018. Accessed Aug 19, 2020. https://solarsystem.nasa.gov/missions/cassini/science/enceladus/.

[50] McFall-Johnsen, Morgan. “NASA Just Revealed An Ocean On Enceladus Contains The Building Blocks Of Life.” ScienceAlert. 2019. Accessed Aug 17, 2020. https://www.sciencealert.com/nasa-just-revealed-enceladus-really-does-contain-the-building-blocks-of-life.

[51] Robitzki, Dan. “Saturn\’s Moon Enceladus Has Nutrient-Rich Oceans.” Futurism. 2019. Accessed Aug 19, 2020. https://futurism.com/the-byte/saturn-moon-enceladus-nutrient-oceans.

[52] NASA. “Titan – In Depth.” NASA Solar System Exploration. 2019. Accessed Aug 19, 2020. https://solarsystem.nasa.gov/moons/saturn-moons/titan/in-depth/.

[53] NASA “Europa.” NASA Solar System Exploration. 2019. Accessed Aug 20, 2020. https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth/#:~:text=From%20ground%2Dbased%20telescopes%2C%20scientists,liquid%20water%20or%20slushy%20ice.

[54] Wall, Mike. “Pluto Has A Buried Ocean — And So Might Many Other Worlds.” Space.com. 2019. Accessed Aug 20, 2020. https://www.space.com/pluto-buried-ocean-may-be-common.html.

[55] NASA. “In Depth | Pluto.” NASA Solar System Exploration. 2019. Accessed Aug 20, 2020. https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth/#:~:text=Pluto%20is%20about%20two%2Dthirds,nitrogen%20frost%20coat%20its%20surface.

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[B] Levesley, Johnson Tear Edexcel GCSE (9-1) Physics. Pearson Education Limited, 2016.

[C] sciencemag.org. “Snowline.” Science.sciencemag.org. n.d. Accessed Aug 22, 2020. https://science.sciencemag.org/content/sci/334/6054/316/F1.large.jpg.

[D] Made by Saya Vekaria 2020

[D] Made by Saya Vekaria 2020

[E] Cowart, Justine. “Ceres – RC3 – Haulani Crater.” Flickr. 2015. Accessed Aug 22, 2020. https://www.flickr.com/photos/132160802@N06/22381131691/.

[F] NASA. “Catalog Page For PIA00104.” 1991. Photojournal.jpl.nasa.gov. Accessed Aug 22, 2020. https://photojournal.jpl.nasa.gov/catalog/PIA00104.

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[J]  NASA. “Catalog Page For PIA17202.” Photojournal.jpl.nasa.gov. 2015. Accessed Aug 22, 2020. https://photojournal.jpl.nasa.gov/catalog/PIA17202.

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[L] New Horizons. “The True Colors of Pluto.” Pluto.Jhuapl.edu. 2018. nAccessed Aug 22, 2020. http://pluto.jhuapl.edu/Galleries/Featured-Images/image.php?page=1&gallery_id=2&image_id=543.

[M] Made by Saya Vekaria 2020

[N] Made by Saya Vekaria 2020

[O] Made by Saya Vekaria 2020

[P] Made by Saya Vekaria 2020

[Q] Internet Archive. “The History of Water on Mars.” NASA/Ames Research Center. 1990. Accessed Aug 22, 2020. https://archive.org/details/AILS_AC90-0559-1.

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About The Author

Saya is an 18 year old currently completing her A Levels. She enjoys studying physics, maths and chemistry. Whilst her future consists of studying maths and computer science at university, her interests lie in astronomy and technology.