What does a planet need to sustain life?

Photo: NASA

Scientists have been discovering exoplanets for years. One prominent mission led by NASA was the Kepler mission which aimed to explore other stars and planets to find a planet that could sustain life. This article will try to give an insight into astrobiology and what life needs to survive on other planets

The basic building blocks of life.

What does life need?

Energy – Complex life (like us) gets energy from the sun but simpler life forms that are deep underground obtain energy from redox chemistry (i.e chemical reactions). If a planet is near a star it will get enough light to support photosynthesis. This is needed for microbes to develop and eventually plants.

Food and nourishment – all life on Earth gets nourishment from only 6 elements which are the “building blocks” of life. These are carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur. Nitrogen is considered particularly important because it is the main component of amino acids (the monomers of proteins).

Make sure there is nothing that can kill you – This including things like intense UV light or ionising radiation. Initial forms of life, like microbes, are more robust so can withstand radiation. However, it would limit the development of complex life forms. For example, humans are sensitive to extreme sunlight because it can lead to sunburns and skin cancer.

Water – This is the most important factor that is required for life and what scientists are searching for. Water must be in a liquid form to be useful (not ice or water vapour). This means that the climate can not be too cold to form ice or too hot to form gas.

The Goldilocks zone.

The Goldilocks zone is the zone of habitable planets that have just the right atmosphere for life. Too thick of an atmosphere means the climate is too hot (like Venus) or too thin means the climate is too cold (like Mars).

Photo: National Geographic. This shows the planets found that are too hot, just right or too cold for life.

The planets scientists find may have changed overtime. For example, river beds have been found on Mars. This indicates that there once was liquid water flowing. However, the atmosphere evolved.

Photo: University of Chicago. This shows the river beds found on Mars.

How does a planet’s atmosphere change?

Atmospheric particles can break free from the gravity of the planet which changes the atmosphere. This happens because the particles have more energy from these potential sources:

  • Sunlight – energy from light is absorbed by atmospheric particles
  • Solar wind – material that comes from the surface of the sun can break away parts of the atmosphere.

Due to this, we know that Mars once may have sustained life but its atmosphere changed. This leads to questions on whether Earth could become Mars or Venus could become Earth (in terms of having a similar atmosphere).

The atmosphere of a planet, therefore, is significant to the way it evolves and whether it can sustain life.

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