The Mars rover, Curiosity - artist's rendering
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Rover studies argon in Martian air

The degree to which the atmosphere of Mars has thinned over time is evident in new measurements from Nasa's Curiosity rover.

It has analysed the different types, or isotopes, of argon atoms in the planet's air.

The study shows how a heavier version of the element has built up relative to a lighter one during Mars's history.

Curiosity scientist Prof Sushil Atreya explained why this is such a key indicator to BBC science correspondent Jonathan Amos.

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