Mars was once wet. But over the course of 4.5 billion years since it came into existence, it’s dried up. As it lost most of its atmosphere, it got very cold and the bulk of its primeval water boiled away into space. The rest seeped underground and froze.
Then, three years ago, researchers announced they’d found something that stirred beaucoup excitement. Even Google celebrated the discovery with a doodle.
They’d detected dark, narrow streaks on many Martian slopes, which appeared to ebb and flow with the seasons. They’d glide downhill in warm seasons and then fade away in winter and reappear the next year. They called them “recurring slope lineae” (or R.S.L.) What but water could behave in this manner, they concluded.
But new research shows that they’re not related to water, but to the flow of grains of sands. So, modern Mars still remains a very dry environment.