Might a Martian rock just an inch wide be the key to unlocking an ancient ocean planet? NASA’s Curiosity rover on July 24 snapped a photo of a wind-carved feature in Gale Crater that eerily resembles the coral of Earth’s reefs. This fragile, branching form, which is only about 2.5 centimeters wide, is the result of processes that have gone on for billions of years since Mars had liquid water.
The origin of the formation is in a familiar geologic process. When water once flowed over the Red Planet, it deposited dissolved minerals into microscopic cracks in the bedrock. When the water evaporated, it left behind cemented mineral veins. Eons later, Martian winds bearing abrasive sand etched out softer surrounding rock, exposing more resilient mineral veins in complex, coral-like forms. “Curiosity has found many rocks like this one, which were formed by ancient water combined with billions of years of sandblasting by the wind,” NASA reported.
This is not the first time the rover has seen such features. On the same day, it recorded a 5-centimeter rock known as “Paposo,” and in 2022, it photographed a flower-rock created by a similar mineral deposition process. These are not just geological oddities; they are physical evidence of Mars’ aqueous past, stored in the mineral veins that once were water conduits.
Preservation is due in large part to Mars’ special erosional climate. Tectonic uplift and water-carried erosion on Earth expose rock units in comparatively short geological time frames, but Mars experiences no active plate tectonics and has been dominated by wind erosion over hundreds of millions of years to billions. Former Curiosity project scientist John Grotzinger characterized the process as wind blowing “like a feather duster” over vast periods of time, slowly uncovering stratified layers like those in Gale Crater’s Murray Formation.
Gale Crater itself, a 154-kilometer-wide impact basin, contains a complicated geological history. The Murray Formation’s 300 meters of stratified mudstone was deposited in a lacustrine environment, eventually capped by cross-bedded sandstones that were deposited by ancient sand dunes. The shift reflects a change from a wetter to much drier climate, a shift preserved in an unconformity that planetary scientist Jessica Watkins described as “significant in that it records not only the transition between environmental regimes, but also substantial erosion of the older lake rocks before the younger wind-driven rocks were deposited.”
Curiosity’s photography of the rock, which resembled coral, used its Remote Micro Imager, a high-resolution, telescope-like camera that can discern fine details at long distances. The instrument, complemented by its suite of spectrometers and environmental sensors, enables the rover to study mineral composition and texture non-destructively. Such non-destructive analysis is vital in detecting possible biosignatures chemical or structural signs that could indicate ancient microbial life.
The rover’s discovery is consistent with a larger collection of evidence that Mars at one time had rivers, lakes, and even oceans. Last June, Curiosity photographed “spiderweb” patterns of ridges boxwork formations created when mineral-laden water seeped into the ground, solidified, and later was uncovered by erosion. NASA said those patterns, as well as the coral-shaped rock, are leftovers from an era when water continued to exist even as the surface of the planet was drying.
Since its 2012 touchdown following a 352-million-mile trek, Curiosity has covered about 35 kilometers, drilling into rocks, examining samples, and constructing a layer-by-layer story of Mars’ environmental history. It found chemical and mineral signs early in its career of past conditions that could have supported life. The coral-shaped rock adds another paragraph to the book, affirming the connection between mineral vein development and long-term water activity.
For planetary scientists, these finds are not mere novelties but integral parts of a systematic geological context. Wind erosion, in the absence of tectonic rejuvenation, has outcropped ancient mineralized veins that could preserve chemical records from Mars’ more aqueous past. On Earth, the same wind- and water-deposited sedimentary rocks have been seen to entomb biosignatures for over four billion years. If Mars did have life at some point, the vein rocks might be some of the prime locations to look for its fossilized record.
