NASA's Curiosity: Martian rocks are advancing our search for extraterrestrial life

Interesting Engineering (IE) examines some of the significant geological features discovered on Mars, including those revealed by NASA's Curiosity rover.

To better understand what geology might teach us about Mars' habitability, we spoke with Dr. Lauren Edger, an astrogeology expert at the U.S. Geological Survey who is working on Curiosity's Gale Crater analysis.

Exploring habitable environments

"The primary goal of the Mars Science Laboratory mission (MSL) is to explore habitable environments," explained Dr. Edger.

"So, we're really interested in the subset of [geological] environments that show prolonged interaction with liquid water, which we know is important for life."

For the MSL mission, NASA's Curiosity rover was created with a focus on the Gale Crater- formed when a meteor hit Mars in its early history about 3.5 to 3.8 billion years ago. At the time of writing (November 21, 2022), the car-sized rover has trekked 18.04 miles (29.04 kilometers) of this region.

Gale Crater was chosen as the landing site since it offers several hints that water has existed there throughout its history.

"My research is focused on this question of when and where life arose in the solar system," Edgar said, adding that she executes this goal by analyzing sedimentary rocks created on the surface of the Earth because they preserve past aquatic and atmospheric conditions.

Edgar expressed that it's intriguing to recognize familiar processes and environments on a different planet because the geology of Earth and Mars is similar in many ways.

"[We] use the Earth as a guide for how to interpret them," she explained.

Discovery of geologic evidence

"In Gale crater, we've discovered geologic evidence for ancient lakes, streams, deltas, and dune fields. We're interested in finding out how long water was present and how these environments changed over time," said Edgar.

"Curiosity is currently exploring a region that showed enrichment in sulfate based on orbital data. We're trying to understand what's causing that signal and what this environment represents," she added.

For example, the area in which Curiosity touched down was at the foot of a layered mountain within Gale crater- a portion of which was an alluvial fan. Alluvial fans are geological structures well known to be produced by water-carried sediments.

Additionally, clays and sulfates, both of which are known to originate in water, can be found in the layers at the mountain's foot.

Sand dunes that resemble those on Earth

The changing mineralogy seen around Mount Sharp (Aeolis Mons) is demonstrated by its layered pattern. This points to a shifting environment on early Mars.

"We've seen a big shift from mostly subaqueous environments (lakes) to now mostly eolian (windblown dunes), and we're curious if this trend will continue or if we'll find additional evidence for past water as we climb higher in the stratigraphy," highlighted Edgar.

For example, the above panorama created by the rover's Mast Camera (Mastcam) showcases varied geological features at Aeolis Mons. This mountain, also known as Mount Sharp, forms the central peak within the Gale crater and rises some 5.5 kilometers (18,000 feet) from the valley floor.

The foreground is filled with gravel and sand ripples, typical of the terrains that Curiosity traveled through to reach Mount Sharp from its landing site.

Although the atmosphere of Mars has a very low density, Martian winds are fast enough to lift and carry the particles and shape them into the little sand dunes you see in the panorama that resemble those on Earth.

Listen to Martian wind in the video below:

Sulfate minerals could be indicative of a change in water availability

The rover found a wide variety of different rock types and evidence of previous water upon landing. Salty minerals, including sodium chloride (common table salt), calcium sulfate (containing gypsum), and magnesium sulfate (like Epsom salt), were present.

According to scientists, the minerals were left behind after streams and ponds dried up, likely billions of years ago. They are hopeful that these minerals can provide some clues as to how and why Mars' environment changed from being more like Earth to the desert it is today.

"It's so exciting that we're at a stage in our science that we can ...investigate these deposits with the same level of detail available in studies on Earth," Edgar said.

The above close-up image showing stick-shaped features on a Martian rock was taken by Curiosity's MAHLI camera at Vera Rubin Ridge on its 1,922nd Martian day.

This is a region on the north slope of lower Mount Sharp, which is well known for being erosion-resistant.

The shape of the features are characteristic of gypsum crystals. It is still debatable as to whether they developed in a lake that was evaporating.

They might have grown considerably later inside hardened rocks, providing information on the chemistry of a wet underground environment.

In either case, these crystals constitute a brand-new kind of proof that supports the existence of long-lasting water and perhaps a habitable climate on Mars.

300-meter-thick layered mudstone could reveal signs of marine processes, which could mean life

"Every day on Mars we have the opportunity to see something that no one has ever observed before on another planet," concluded Lauren Edgar.

As Curiosity traversed the Gale Crater, it came across the Murray Formation. This is a 300-meter-thick layered mudstone named in honor of the late Bruce Murray, who was a professor of planetary science at Caltech and the former director of the Jet Propulsion Laboratory (JPL), which Caltech manages for NASA.

Mudstone forms when fine-grained mud is compressed over time. This is an ideal location for the rover to investigate as the bands may reveal signs of marine processes which occurred during or after the sediments were deposited. Such bands could also disclose ingredients that could have supported life.

'Valles Marineris': Did life thrive on Mars, when it was more seismically active?

And just because we have not observed plate tectonics on Mars today, does that mean we should assume that this has always been the case throughout Mars' history? Perhaps not when considering Valles Marineris- the planet's iconic canyon system, located southeast of Olympus Mons, a large shield volcano on Mars.

The canyons stretch for about 2,500 miles and cut up to 4.3 miles into Mars' surface. Better yet, the network of these crevasses is four times deeper and five times longer than the Earth's Grand Canyon, stretching 277 miles long, 18 miles wide, and one mile deep.

According to studies, the Martian canyon has signs of large-scale strike-slip fault zones comparable to Earth's plate-bounding transform faults like the San Andreas and the Dead Sea faults.

These observations show that Mars may have experienced plate tectonics in at least some regions during its geological history. From moving continents, causing earthquakes and volcanoes, and determining the composition of the air we breathe, plate tectonics play a crucial role in sustaining life on Earth. Did life similarly thrive on Mars when it was more seismically active?

Missions like Curiosity may one day reveal an extraterrestrial abode we can call a second home

Currently, new missions with new instruments and terabytes of data are providing novel clues into the geological evolution of Mars. Thanks to rovers like Curiosity, we've come a long way from recognizing Mars for just its red (iron-rich), somewhat inhospitable dusty surface.

We now know from information about its ancient lakes, mountains, and canyons, that Mars has not always been this way.

"There's a lot we can learn from orbital observations of Mars. But, the opportunity to ground-truth those observations and conduct analyses (similar to what we would do as geologists on Earth) is a really exciting experience. That's what inspired me to be a part of this mission," she added.

For now, the nuclear-powered rover will continue its observations of geology, as well as climate and radiation, breathing in all kinds of Martian particles just so that one day we may find substantial clues and signs that support life.

And who knows, the information from Curiosity or future rovers might help scientists and future generations find another abode we can actually call home. No doubt SpaceX will be on the watch.