The answer was blowing in the solar wind.
Our favorite images of the week
Findings from the MAVEN spacecraft suggest solar eruptions helped to destroy Mars' atmosphere
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Plus adorable echidna puggles
A look at the spacecraft's first year studying the Martian atmosphere
The red planet is literally shrouded in mystery
The newest NASA probe will sniff the Martian sky.
MAVEN will try to decipher the history of Mars' atmosphere and how it was lost.
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