Mars is covered in evidence of ancient lakes, rain and snow — but scientists aren't sure how that's possible

Valleys on Mars suggest the Red Planet was once covered in flowing water — but it's still a mystery how that could have been.

https://www.space.com/the-universe/mars/mars-is-covered-in-evidence-of-ancient-lakes-rain-and-snow-but-scientists-arent-sure-how-thats-possible