ESA title
Comparing the atmospheres of Mars and Earth
Science & Exploration

What is a trace gas?

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ESA / Science & Exploration / Human and Robotic Exploration / Exploration / ExoMars

A trace gas makes up less than 1% by volume of a planet’s atmosphere. Trace gases in the martian atmosphere include methane, water vapour, nitrogen dioxide and acetylene. Although making up a very small amount of the overall atmospheric inventory, methane in particular holds key clues to the planet’s current state of activity.

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