To date, astronomers have discovered about 209 extrasolar planets; that is, planets outside our solar system. From Earth, it is quite difficult to even detect them, much less learn anything about them. We haven’t been able to determine much about these planets—usually only the mass—though we’ve been able to get glimpses of atmosphere in a couple cases.
Of course, we have no idea if there is life on other planets, or how we might detect it. One way to think about it is to imagine what other life forms might think of Earth if they were to stumble across it.
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