Mars wasn’t always the frozen, barren desert that it is today. We know that water existed at one point on the red planet, but what did the environment look like? Where did the water go, and more importantly, was there ever life? 

Thanks to incredible findings from NASA’s superstar rover, The Curiosity, we’re starting to piece together the puzzle of Mars’ ancient history, and the journey starts in what was once an oasis on the planet’s surface, now a treasure trove of discovery that tells the story of Mars’ multi billion-year history.

The Curiosity landed on Mars’ surface back in 2012. At about the size of a car, the rover is jam-packed with advanced scientific equipment like hi-res cameras, lasers, and robotic arms to reach down and collect samples.

NASA/JPL

Curiosity is truly a rock star of a rover. Her original mission was only supposed to last two years, but she’s been so successful in zooming around Mars, gathering valuable information, that it was extended indefinitely by NASA and President Obama.

NASA

The selfie-taking, Twitter-posting rover is credited with two major discoveries: liquid water once existed on Mars and the ancient planet supported conditions for microbial life (this we know because, in 2013, she drilled a sample of ancient mud containing nitrogen, oxygen, and carbon, some of life’s building blocks).

NASA/JPL-Caltech

Curiosity’s current mission, however, is to explore the Gale Crater, a 100-mile wide basin that scientists believe was once an enormous oasis and lake bed. This area is hugely important because recent evidence published in a Nature Geoscience paper suggests it may have been the site of biological life.

The crater itself is the ancient remnant of a massive impact that occurred millions of years ago. Sediment was first carried by water and wind to the crater floor, layer by layer, and then as the environment dried, harsh winds carved the sediment into the towering Mount Sharp.

It’s the slopes of Mount Sharp, where Curiosity is now, that reveal different layers of sediment, going back in time, similar to the Grand Canyon here on Earth. These different layers act like a visual guide to the planet’s surface during these different eras.

“We went to Gale Crater because it preserves this unique record of a changing Mars,” said author William Rapin of Caltech. “Understanding when and how the planet’s climate started evolving is a piece of another puzzle: When and how long was Mars capable of supporting microbial life at the surface?”

This visual guide to the planet’s surface is just one small part of Mars, but it gives important insight into not just what occurred, but when. It’s this information that proved some of the basic assumptions scientists about Mars’ history to be dead wrong.

We use our understanding of the geology here on Earth to help us piece together the geological history on Mars. And luckily, there is a place here that strongly resembles the Gale Crater on Mars: the salt lakes of South America’s Altiplano.

This high-altitude plain is cold, dry, and features streams and rivers that flow down from mountain ranges into a closed basin, just like on Mars. The Altiplano surface even looks eerily similar.

So Rapin and his team had the idea that by studying how water flows through the Altiplano, they could better understand the Gale Crater system on Mars. Turns out, the data sent back from Curiosity confirms this was the right direction.

“During drier periods, the Altiplano lakes become shallower, and some can dry out completely,” Rapin, below, said. But during wetter periods the water can swell and overflow. This was precisely what happened on Mars and explains the rocks enriched in mineral salts that Curiosity found.

If you could watch this history unfold on Mars by fast forwarding through time, you would see waterways swell with water, then dry out, and repeat again and again, over the mind-bending time span of millions of years.

But what about evidence of life? Curiosity discovered evidence of clay on the side of Mount Sharp, meaning that a significant amount of water mixed with the sediment there over a long period of time. Combined with the chemicals found, this suggests favorable conditions for microbial life.

Now that Curiosity has found evidence of so much clay and ancient mud, and experts can cross-reference this with rough estimates of when that sediment was there, scientists made the startling discovery that proved wrong what had been the common assumption for decades.

NASA

Mars’ water didn’t disappear all at once, and it didn’t change from a wet climate to a dry one all at once, either. Instead, the environment slowly transformed over millions of years, with water levels rising and falling, taking longer than previously thought.

NASA

This means that if there were life on Mars, it may have been around a little bit later, and if that’s the case, we might be able to find it a little easier. We just need to know where to look.  

Curiosity’s younger sibling, Perseverance, is set to launch in 2020 and is based on a refined version of its older sister’s design. The rover is packed with state-of-the-art technology, including an ultraviolet laser to determine fine-scale mineralogy and detect organic compounds.

Curiosity’s power system has a few more years of life left before it will start to degrade. Until that time comes, careful management of power will allow her to keep taking samples, exploring terrain, and snapping selfies. 

In the meantime, thanks to our hard-working friend Curiosity, and a little bit of insight from natural processes on our own planet, we now have a deeper understanding of Mars’ ancient history. Still, there remains a lot to be discovered.

1. Blueberries: Okay, obviously these aren’t real berries on the surface of Mars, but they sure do look like them! There’s an entire field of these little spherical, blueish rocks but scientists are still working on how they got this way.

NASA

2. Dust Devil: The Opportunity rover caught this dust devil on camera, confirming scientists’ theories that the little twisters occur on Mars. Future rovers now come with their own protections for dealing with such weather hazards.

NASA

3. Face on Mars: The creepy “face” on Mars is probably the most famous image, first captured by the Viking 1 and 2 orbiters. Although the face is unmistakable in early low-res photos, new high-quality images have show the mountain structure actually doesn’t look much like a face at all.

NASA

4. The Bone: Conspiracy theorists went crazy when images of this bone-shaped rock appeared on Mars’ surface. The fact is that there are a lot of rocks on Mars. A LOT. Some of them are bound to look like stuff we recognize.

NASA

5. Morse Code: We all know about crop circles, but what about morse code… from space? These sand dunes on Mars look eerily similar to morse code, prompting scientists to translate them to this message: “NEE NED ZB 6TNN DEIBEDH SIEFI EBEEE SSIEI ESEE SEEE.”

NASA

6. The Pyramid: After getting ahold of this image of what clearly looks like a pyramid, some people insisted it was a message from an alien civilization. NASA, however, has downplayed it. “It is a rock,” said Dr. Jim Bell, right, of the Curiosity program.

NASA

7. The Hole: Located near Mars’ south pole, this perfectly shaped hole caught the attention of scientists, who could see the frozen carbon dioxide ice at the bottom. We’ve so far only seen The Hole from orbit, but it’s estimated to be a few hundred meters across.

NASA

8. The Iguana: One has to admit, this rock does look like an iguana! “To say it’s just a rock would be very closed minded to the evidence at hand,” said owner of the UFO Daily Sightings Blog, Scott C. Waring.

NASA

9. Waffle-shaped island: This 1.2-mile wide island looks strangely like it just came off the waffle iron and is ready to be drenched in maple syrup. In reality, it’s near an ancient volcano so it probably got that way from criss-crossing lava flows.

NASA

10. Fish-shaped rock: If you look closely, you might be able to make out this rock formation that looks like a fossilized fish. Don’t jump to conclusions, though. NASA says that Mars never had enough oxygen in its atmosphere to support complex life. “Thus, large fossils are not likely.”

NASA

11. Evidence of Liquid Water: Recent discoveries at the massive Gale Crater site indicate that liquid water persisted on Mars for perhaps a million years or longer, and didn’t disappear all at once, changing a commonly held assumption about the planet’s evolution.

NASA

12. Jelly Donut: NASA’s Opportunity found this rock that looks strangely like a jelly donut, but when it went back to check it out, it was gone. Did an alien eat it? Nah, turns out the rover’s wheels accidentally ran it over and flipped it in another direction.

NASA

13. Dragon Scales: These scaly-looking hills have been nicknamed “The Dragon Scales” for their uncanny similarity to reptilian skin. However, it’s thought that this region was eroded by ancient rivers, resulting in the scaly features.

NASA

14. Scratch marks: If those “dragon scales” weren’t weird enough, these lines on the surface that were captured in 2017 look strangely like scratch marks. Scientists think they are the result of dry ice sliding down the slope of this mountain.

NASA

15. The “Jake Matijevic” Rock: This striking rock caught the attention of NASA’s Curiosity rover as she was exploring the area. The rock (named Jake Matijevic after a prominent engineer) is made of unusual minerals typically found in Earth’s core.

NASA

16. Little Colonsay: This strangely shiny object nicknamed “Little Colonsay” was picked up by the Curiosity rover and looked very out of place among the other red rocks in the area, leading them to believe it was a meteorite. More studies have to be done to fully determine where it came from.

NASA

17. Egg Rock: Speaking of meteorites, check out this egg-shaped rock that Curiosity discovered. The strangely smooth, globular object was scanned by the rover’s laser-firing spectrometer and found to be an iron-nickel meteorite fallen from the Red Planet’s sky.

NASA

18. Spheres: A field of these strange, spheroid rocks were discovered in 2012 at the Kirkwood outcrop. They’re quite different from the “blueberries” found elsewhere on Mars, as they’re smaller and more densely accumulated.

NASA

19. Avalanche: Just like on Earth, when temperatures start to warm up in the Spring, melting ice and frost (made of CO2 on Mars) can trigger avalanches down steep cliffs, like this one here photographed in 2010.

NASA

20. Lava Coils: These interesting swirl shapes look almost too perfect to not have been made by intelligent design, but they’ve been confirmed to be the result of ancient flowing lava.

Andrew J. Ryan