Scientists suspect that the surface of Mars was once teeming with water, a lush oasis full of river systems and lakes — until a dramatic change in the planet’s magnetic field caused it to lose most of its atmosphere, turning it into the arid hellscape we know it as today.
Now, an unusual new rock collection discovered by NASA’s Perseverance Mars rover suggests the Red Planet’s ancient past was even wetter and more tropical than scientists previously thought, an intriguing new wrinkle in our efforts to figure out if the planet was once habitable.
As detailed in a new paper published in the journal Communications Earth & Environment, a team of researchers analyzed the rocks, which feature intriguing, light-colored dots and range in size from pebbles to boulders. They suspect it’s aluminum-rich kaolinite clay which on Earth forms after millions of years of wet, rain-filled weather leeches all other minerals from it.
“Elsewhere on Mars, rocks like these are probably some of the most important outcrops we’ve seen from orbit because they are just so hard to form,” said coauthor and Purdue University professor of planetary science and NASA Perseverance team member Briony Horgan in a statement. “You need so much water that we think these could be evidence of an ancient warmer and wetter climate where there was rain falling for millions of years.”
On Earth, kaolinite clay is most commonly found in tropical climates like rainforests, suggesting Mars may have once been home to a lush oasis. The team compared the rocks with samples from San Diego, California, and South Africa, and found intriguing similarities.
“So when you see kaolinite on a place like Mars, where it’s barren, cold and with certainly no liquid water at the surface, it tells us that there was once a lot more water than there is today,” lead author and Purdue University postdoctoral research associate Adrian Broz added.
The rover found fragments of kaolinite in a number of places along its path along the Jezero crater, which is suspected to be an enormous, dried-out lake bed — a finding that left scientists with a conundrum.
“They’re clearly recording an incredible water event, but where did they come from?” Horgan said in the statement. “Maybe they were washed into Jezero’s lake by the river that formed the delta, or maybe they were thrown into Jezero by an impact and they’re just scattered there. We’re not totally sure.”
Larger outcroppings of light-colored rocks could help them solve the mystery, but that’s something that will require Perseverance to have a much closer look.
“But until we can actually get to these large outcroppings with the rover, these small rocks are our only on-the-ground evidence for how these rocks could have formed,” Horgan said. “And right now the evidence in these rocks really points toward these kinds of ancient warmer and wetter environments.”
“All life uses water,” Broz added. “So when we think about the possibility of these rocks on Mars representing a rainfall-driven environment, that is a really incredible, habitable place where life could have thrived if it were ever on Mars.”
Besides painting a fascinating picture of an ancient tropical oasis on Mars, the researchers believe the rocks could allow us to glean new insights into how the Red Planet turned into a barren wasteland — an extreme shift that remains a mystery to this day.
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