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Wait, there are no cars on Mars. Could a hotter sun be warming up Mars climate as well?

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the article that you cite says:
Like Earth, Mars has seasons that cause its polar caps to wax and wane. "It's late spring at the south pole of Mars," says planetary scientist Dave Smith of the Goddard Space Flight Center. "The polar cap is receding because the springtime sun is shining on it."

it doesn't mention anything about increased solar activity being responsible for its ice caps melting.