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Scientists announced that they have discovered signs of water on Mars in a NASA press conference Monday morning, fueling questions about whether life could survive on the red planet. Naturally, jokes flowed on Twitter, including barbs from actors, comedians, writers and YouTube celebrities. Some even made jokes about actor Matt Damon, who plays a stranded astronaut in The Martian, which opens in theaters this weekend. Here is a glimpse at some of the funniest reactions to the out-of-this-world news on Twitter:

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Write to Olivia B. Waxman at

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