Ancient Mars may have harbored life for hundreds of millions of years

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For years, the conventional wisdom was that Mars existed as little more than a cold, barren dust ball in space. The idea that it once supported life was considered unlikely. But then we started sending probes the the Red Planet, and more recently rovers like Curiosity. Since its arrival in 2012, Curiosity has covered more ground than all previous rovers, and now mission scientists are comfortable saying that Mars would have been capable of harboring life for hundreds of millions of years in the past.

Curiosity landed in a region known as Yellowknife in Gale Crater, and has been making its way up to higher elevations around Mount Sharp, which is in the middle of Gale Crater. This gives it a chance to investigate the strata as it ascends, essentially scanning the Martian past.

The new proclamation of Mars as a potential long-term home to ancient life comes from Curiosity science team member John Grotzinger, who spoke on the topic at a recent meeting of the American Geophysical Union (AGU). We’ve known from samples all the way back to Yellowknife that Gale Crater most likely played host to a vast lake and stream system, but it was not present continuously. That doesn’t necessarily mean everything living there disappeared with the water, though.

According to Grotzinger, analysis of Curiosity data from various levels in Gale Crater paint a picture of fresh, neutral pH water that got more acidic and salty over time. The lakes also completely dried up and refilled repeatedly over the course of millions of years. Despite this, simple microorganisms could have persisted in the groundwater, ready to take advantage when standing water again flooded the surface.

Curiosity has also identified a great diversity of minerals on Mars, which points to a complex chemical history — just the sort of thing life requires. The rover has detected many of the same minerals we have on Earth, including clays, magnetite, and boron. There’s even silica, which scientists are particularly happy about. On Earth, silica has been good at preserving microscopic fossils. If life did exist on Mars in the past, we might find strong evidence for it in silica deposits.

This is all assuming alien life on Mars operates by the same rules as life on Earth. That’s certainly not a given. Even life on Earth can seem almost alien at times. Single-celled extremophiles can survive (and even thrive) in conditions too hot, acidic, or salty for any other organism. Maybe something like that lived (or lives?) on Mars. We might find more clues when NASA’s 2020 rover project heads to the Red Planet.