There Could Be an Extremely Simple Reason Why Mars Isn't as Suitable For Life
4 min read
fairly difficult
We often talk about the strong similarities between Earth and Mars, but it's the differences that are likely behind why one planet has life and the other doesn't – at least, no life we've found so far.
Specifically, new research suggests it could be down to the size discrepancy. The diameter of Mars is just 53 percent that of Earth's (just over half the size), and that would make it impossible for Mars to hang onto volatiles that we know are vital for life – such as water.

"Mars's fate was decided from the beginning," says planetary scientist Kun Wang of Washington University in St. Louis.

"There is likely a threshold on the size requirements of rocky planets to retain enough water to enable habitability and plate tectonics, with mass exceeding that of Mars."

Although there are many differences between Earth and other terrestrial planets in the Solar System, it can be difficult to ascertain which factors are conducive to the emergence of life, and which factors hinder it.

But we can look at some of the things life on Earth needs in order to exist, and work from there.

One thing that life on Earth requires is liquid water, so conditions that enable the presence of liquid water is one of the key items on the planet habitability checklist. We know that Mars used to have surface water – we've seen evidence of it in Martian meteorites that have made their way from Earth, excavated from the red planet when the Solar System was still young. Today, however, Mars is dusty, dry and desolate, and any water on its surface is frozen.

The transition from a relatively wet planet to arid dustbowl is sometimes attributed to Mars's lost magnetic field. But it's possible that other factors play a role in the retention of volatiles, such as the surface gravity of a…
Michelle Starr
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