Mars was once wetter and warmer, and very possibly a congenial environment for life as we know it. Today it looks mighty dead, with all due respect. If there's life, it's cryptic.
Mars just ain't the planet it used to be. It's a desert world, with a pitifully thin atmosphere less than 1 percent the density of Earth's. That leaves the surface exposed to radiation and prone to huge temperature swings from day to night. If Mars was ever blue or green, it is surely red now. What happened?
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