NASA’s Curiosity rover has found more evidence of a rich and varied history on Mars.
The latest findings were published in a paper in Earth and Planetary Science Letters. It discusses samples drilled from three different locations inside Gale Crater, a basin 154 kilometers (96 miles) wide that once hosted an ancient lake.
Curiosity is currently making its way up Mount Sharp, a 5.5-kilometer-high (3.4-mile-high) peak in the middle of Gale Crater. And as it does so, it can see sediments dropped at different points in the lake about 3.5 billion years ago. These were described in the paper by scientists from NASA’s Astromaterials Research and Exploration Science (ARES) Division.
"These layers were deposited about 3.5 billion years ago, coinciding with a time on Earth when life was beginning to take hold,” NASA’s Elizabeth Rampe, lead author on the study, said in a statement. “We think early Mars may have been similar to early Earth, and so these environments might have been habitable.”
What’s particularly exciting is, as mentioned, the change in the samples. It shows that the pH level and oxygen levels may have varied in the water – something backed by another paper earlier this month. This suggests differing environments in which microbes could have taken hold.
The samples were taken in a region called Pahrump Hills on lower Mount Sharp in 2014 and 2015. The lowest samples show minerals from a primitive magma source. Further up, scientists found tridymite, a perplexing mineral because it forms on Earth from partial melting of our crust – but Mars never had plate tectonics.
Elsewhere, scientists found clay minerals, which usually form in liquid water with near-neutral pH. These could suggest environments that were suitable for life. Also discovered was jarosite, a salt that forms in acidic solutions.
As to why the samples are so varied, well, that isn’t clear. NASA discusses a couple of possibilities, though. One is that the “lake waters themselves at the base were oxidizing, so either there was more oxygen in the atmosphere or other factors encouraged oxidation.”
Alternatively, it may be that groundwater moved into the region after the lake. This was more acidic and oxidizing than the water before it, giving rise to some of the differing features we see today.
Whatever the cause, this study further proves just how varied Mars once was. We are almost certain now that it used to have water on its surface. Now we just need to find out what it was like to be in that water.