An artistic representation of the solar system

Activity: Location, location, location – space edition

It is almost inevitable that at some point in the future humans will be living on another world as well as the Earth. Where could we go?

In scouting out potential places for humans to live, there are many constraints to consider:

  • Temperature: The human body is good at regulating its temperature but cannot withstand very long periods at over 60ºC. It’s not as straightforward in the cold, but below water’s freezing point (0ºC), the human body cannot withstand it for more than about a week and a half. Clothing and protective gear can help.
  • Gravity: Sure, floating around is fun, but from a practical standpoint, setting up life on a new planet would be difficult without much holding us down. Gravity contributes to a planet, moon or other body’s escape velocity – the speed needed to leave it and reach outer space. With very low gravity, there’s little stopping you from flying off into deep space, where you would not last long.
  • Atmosphere: The air humans breathe is almost entirely a combination of nitrogen (78 per cent) and oxygen (21 per cent), though exact quantities differ based on barometric pressure. Our bodies need the oxygen for essential processes and convert it to carbon dioxide via respiration. If a planet doesn’t have any native oxygen, how might we get it?
  • Liquid water: The human body is 70 per cent water. The presence of liquid water often indicates that the temperature conditions are right for life as we know it. (More on this in ‘Planetary puzzles’.)
  • Carbon: An essential element of all building blocks of life – carbohydrates, fats, proteins and nucleic acids. (See our explanatory article on carbon for more.)
  • Radiation: High-energy electromagnetic radiation from the Sun can damage our skin even on Earth without proper sun cream. Without the Earth’s thick atmosphere and protective magnetic field, our bodies would not be able to withstand the destructive forces. How might we protect ourselves on planets where the barriers are not as strong?

Some scientists use the Earth Similarity Index (ESI) to determine which planets are most similar to Earth (see infographic). The index runs from 0 to 1 (1 being an exact replica of Earth). A planet’s score is based on radius, density, escape velocity and temperature. Anything over 0.8 is considered very high – and that planetary body is very likely to have a rocky composition.

Interestingly, in 2014 two planets were spotted that have been described as ‘twins’ to Earth, both with a high ESI – Kepler-238.b and Kepler-62e. It’s important to remember, however, that they are very, very far away – 4,700 light years and 11,900 light years, respectively. So even if they were perfect for humans, how would we all get there?

Your turn

Here is a brief selection of details of the conditions and resources available on four different planetary bodies. Think about the challenges you would face on each of these worlds and what you might need to survive. (Note: water is good for more than drinking and washing – think what it is made of.)

Split into four groups, each taking one of the bodies listed below: the Moon, Mars, Titan and Kepler-22b.

GROUP 1 The Moon
Diameter 27% of Earth’s
Gravity 17% of Earth’s
Atmosphere None
Water Water ice found, particularly near South Pole
Temperature Swings wildly from below freezing to above boiling between day and night
Length of day Almost a month
GROUP 2 Mars
Diameter 53% of Earth’s
Gravity 38% of Earth’s
Atmosphere Very thin (1% as dense at Earth’s) and 95% carbon dioxide
Water Significant water reserves locked up in ice
Daily radiation dose 0.66 sieverts (approximately 13 times the annual limit for a nuclear worker)
Temperature -150°C to 20°C
Orbital period 687 days
GROUP 3 Titan (one of Saturn’s moons)
Diameter 40% of Earth’s
Gravity 14% of Earth’s
Atmosphere 1.44 times denser than Earth’s and 98.4% nitrogen
Temperature -180°C
Orbital period 16 days around Saturn, which has an orbital period of 29 years
Other resources Over 100 times more hydrocarbons than on Earth
GROUP 4 Kepler-22b (exoplanet)
Distance from Earth 620 light years
Distance from host star About 85% of Earth’s distance from the Sun
Diameter 2.4 times Earth’s
Mass Approximately 50 times Earth’s
Temperature 22°C (if it has a similar greenhouse gas profile to Earth)
Orbital period 290 days
Water Unknown

Group activity

Research your body and come up with suggestions on how human life might thrive there. Use the list above to address issues of temperature, liquid water, gravity and so on.

But also think further – what things would humans need to survive long-term on this body? How would we meet daily needs? Think about food sources; think about reproduction. Are there any more factors to consider?

Each group should present back to the others, making the case for their body. Part of this will be about data and about your ideas, but an important element will be how you communicate the results of your research back to the class in a clear, coherent manner.

At the end, take a vote. Which location won out – and why?

Share the results of your vote with us – either by email ( or on Twitter @WTeducation, using the hashtag #spaceplace.

Solo activity – independent research

If you’re on your own, do a little independent research on all four bodies. On which body do you think humans would have the best chance of survival – and why? How would you address the various issues constraining human life?

Share the results of your vote with us – either by email ( or on Twitter @WTeducation, using the hashtag #spaceplace.

Lead image:

Philippe Put/Flickr CC BY

Downloadable resources

About this resource

This resource was first published in ‘Space Biology’ in June 2015.

Statistics and maths, Ecology and environment, Health, infection and disease
Space Biology
Education levels:
14–16, 16–19, Independent research projects