How It Works

Why is Earth bigger than Mars?


When compared to our planet Mars is very tiny, possessing around ten per cent of Earth’s total mass. This has long puzzled experts in planetary formation, as in the standard model objects of a similar size group together through a process known as accretion. Rocks essentially incorporate other rocks to create mountains, then these accumulate to form city-sized objects, and so on. This formation model works well for Earth and Venus, but predicts that Mars should be much larger than it actually is, potentially even larger than our home planet.


The brand new method, known as Viscously Stirred Pebble Accretion (VSPA), explains why Mars is much smaller than Earth


Thanks to a brand new formation model, scientists are now certain they have found out why Mars is much smaller than Earth. This new theory states that planets form from miniature bodies known as pebbles, which are formed gradually from dust particles. These pebbles eventually form objects the size of asteroids, which become enormous planets after a relatively short period of time.

However, the new theory finds that not all asteroids are as well positioned to accrete pebbles and grow into planets. It suggests that huge asteroids would have been able to grow very quickly in Earth’s location, but the place that Mars inhabits has much less aerodynamic drag, which makes it much harder to capture pebbles floating in space. This is why Mars never grew to the size of Earth.

This new modelling technique also helps to explain the formation of our Solar System’s gas giants: Jupiter and Saturn.


The new model will hopefully be used to explain the formation of the gas giants in our Solar System


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Plus, take a look at:

Mars mystery solved: NASA confirm the presence of flowing water on the Red Planet

Exploring Mars in new ways

Colonies on Mars: Interview with Chris Lewicki