Earth is the only known planet that can support human life. However, with advances in technology, it may one day be possible for humans to live on other planets in our solar system. Selecting a new planet to inhabit would require finding one that meets certain criteria to support human survival.
Why look for other planets to live on?
There are a few key reasons humans may eventually need to inhabit a planet other than Earth:
- Overpopulation – As the human population grows, we may run out of adequate resources and living space on Earth
- Climate change – Environmental changes to Earth could make parts of the planet uninhabitable in the future
- Catastrophic events – An asteroid collision or other disaster could make Earth unsafe
- Space exploration – Humans may want to colonize space for scientific discovery and adventure
Having a “backup planet” could ensure the survival of the human species if Earth becomes unlivable. Additionally, learning to live on other celestial bodies expands scientific knowledge and human presence in space.
Criteria for a habitable planet
For a planet to support human life, it must meet certain minimum criteria:
- Distance from the Sun – It cannot be too close or too far from the Sun. The planet must be in the circumstellar habitable zone, where temperatures allow for liquid surface water.
- Similar size to Earth – A planet around the same size as Earth is more likely to have comparable gravity and atmospheric conditions.
- Rocky composition – A solid, rocky planet maintains conditions on the surface that can support an atmosphere and standing water.
- Orbit and rotation – The planet should have a stable orbit and moderate rotation to create Earth-like day/night cycles and seasons.
- Magnetic field – A global magnetic field protects the planet from solar radiation and helps retain its atmosphere.
- Air and water – The planet must have water sources and an atmosphere with gases like oxygen and nitrogen to sustain human respiration and plant life.
Very few celestial bodies meet all these criteria. Of the planets in our solar system, Mars comes closest but still lacks crucial elements like a breathable atmosphere.
The case for Mars
Mars remains the most viable option for human habitation outside of Earth. Here’s how it measures up to the habitability criteria:
- It’s located in the habitable zone, though on the outer edge. Its greater distance from the Sun makes its surface colder than Earth’s.
- Mars has a similar land mass to Earth. Its diameter is just over half of Earth’s.
- The planet is rocky with evidence of ancient river beds and mineral deposits.
- A Martian day is 24 hours and 37 minutes, compared to Earth’s 24 hours. It has a tilted axis like Earth, creating seasonal changes.
- Mars does have a weak magnetic field generated by electric currents in its molten metallic core.
- There is water in the form of polar ice caps and traces in the soil. But the atmosphere consists mainly of carbon dioxide, with little oxygen.
Mars lacks a breathable atmosphere for humans. But technologies like terraforming could potentially enrich the atmosphere over time. Growing plants on Mars could also produce more oxygen. We could also set up biodomes with Earth-like conditions to live in while gradually changing the external environment.
Terraforming would involve transforming the environment of Mars to resemble Earth’s more closely. Some potential methods include:
- Heating the planet to release CO2 from ice caps – This could thicken the atmosphere
- Importing ammonia to increase greenhouse gases
- Algae or lichens could be introduced to convert CO2 into oxygen
- Artificially created oceans could help increase temperature, oxygen levels, and humidity
Using technology to terraform Mars is theoretically possible but extremely challenging. It would likely take hundreds or thousands of years to make noticeable differences. So we may need to start with dome settlements first.
Other planets and moons
No other planet in our solar system meets the basic criteria for human survival. But some of the moons around gas giants show potential for habitability in the future.
Europa is one of Jupiter’s moons. It may have a global saltwater ocean below an icy crust. This ocean could contain 2-3 times as much water as on Earth. Europa likely has volcanic activity which could provide geothermal energy. But its surface is frozen at -260°F (-160°C). It lacks a magnetic field and has a thin oxygen atmosphere. Future missions could look for possible signs of life in Europa’s hidden ocean.
Saturn’s moon Titan has lakes and rivers of liquid methane and ethane on its surface. It contains organic compounds that could support primitive lifeforms. But Titan’s extremely low surface temperature of -290°F (-180°C) makes it inhospitable for humans. The atmosphere is poisonous, containing high amounts of nitrogen and methane gas. However, we could potentially build floating settlements on Titan’s lakes.
Like Europa, Enceladus is an icy moon with a global ocean underneath. Geysers erupt from this ocean, shooting water into space. So Enceladus likely has easily accessible water sources. But it has no breathable atmosphere and -330°F (-201°C) surface temperatures. A settlement would need to harness geothermal activity for heat and power generation.
Colonizing the moon
Before attempting to inhabit any other planets or moons, it may be wise to start with a lunar colony first. This would help us gain experience on the challenges of settling a harsh extraterrestrial environment.
The moon’s proximity to Earth and lower gravity make transportation easier. Water ice deposits at the poles could provide drinking water. Solar power can produce electricity on the moon. Bases could be built underground or inside lava tubes to shield inhabitants from radiation, temperature swings, and micrometeorites. But the moon lacks an atmosphere, water, and soil for growing food. So settlements would require technology to recycle resources and import supplies from Earth.
Future prospects for space colonization
While Mars holds the greatest viability for human colonization in our solar system, future discoveries could reveal even better options. SpaceX CEO Elon Musk has proposed making humans a multiplanetary species starting with a Mars outpost. As we find additional habitable exoplanets beyond our solar system, humans may someday spread across the galaxy.
With radical advances, we might be able to terraform other worlds more quickly. Or use technologies like nanotechnology, artificial gravity, fusion power, and suspended animation for deep space travel. Giant space habitats could even be engineered to replicate Earth environments while journeying for centuries to distant stars.
Prospects for inhabiting other celestial bodies currently remain theoretical. But technology is progressing rapidly. The availability of vast resources across space could allow expansion beyond Earth’s limited carrying capacity. In the future, we may no longer need to depend solely on this one small planet.
Mars remains the top contender for human habitation outside our home planet. But we still have much work ahead before colonizing other worlds can become a reality. Technologies for surviving hostile environments must be developed. And the great distances and travel times to planets in our solar system pose major obstacles.
While alternate living spaces like Mars can act as a backup, realistically, Earth is still the only planet that will sustain human civilization for the foreseeable future. We must continue to care for our planet’s health and habitability while taking small steps out into the cosmos.