The Curiosity Rover: A Martian Adventure

Fortunately, NASA’s Curiosity rover is a rather hardy little machine. Unfortunately, despite even the best engineering Earth has to offer, its days are numbered.

But perhaps we are getting a little ahead of ourselves. Before talking about death and destruction, we should probably tell the story of how it all started. So, let’s rewind…

Curiosity’s daring beginnings

The landing phase of Curiosity's journey, dubbed “Seven Minutes of Terror” by NASA, was a heart-pounding experience. Radio signals took 13 minutes and 48 seconds to travel from the spacecraft to Earth, creating a total round-trip time of about 28 minutes. 

The problem? 

When it entered Mars’ atmosphere, Curiosity was traveling 13,000 miles per hour (20,000 km/h). That speed gave it just seven minutes to decelerate and land. In other words, the landing sequence took place much faster than NASA was able to send and receive transmissions. Curiosity was entirely on its own.

And the rover’s sheer size made these seven minutes of terror extra terrifying.

Curiosity is roughly the size of a small SUV and weighs 2,000 pounds (900 kg). So the typical landing method, in which a craft deploys landing bags and bounces to a stop, wasn’t an option. Things had to get technical.

Using a complicated sequence of events involving a supersonic parachute, retrorockets, and a skycrane, Curiosity safely landed on Mars on August 6, 2012 at 05:17:57 UTC. The most dangerous part of the mission was over. But things weren't exactly easy after this.

The rover came to rest at the foot of Mount Sharp, a layered mountain located on Gale Crater. Gale Crater is known to have a wet history, which is partially why it was selected as the landing site. However, to sufficiently check for traces of water, Curiosity has to roam an area about the size of Connecticut and Rhode Island combined.

Shortly after touchdown, Curiosity started its long journey, moving along the crater at a staggering speed of 295 feet per hour (90 m/h). 

‍The tools at Curiosity's fingertips

As the rover travels, it has to maneuver over many obstacles. Fortunately, it’s equipped with technologies that let it roll over anything… that’s up to 20 inches (75 cm) high. On rocky Mars, you can bet there are a lot of obstacles.

And, of course, Curiosity has an arsenal of cutting-edge science tools that it deploys along the way. In fact, Curiosity’s payload of gear was more than 10 times as massive as its predecessors. So, what’s on board?

First things first, it has to scope out its environment. An array of cameras help Curiosity assess its terrain. It even has its own magnifying lens to take close-up images that can reveal details smaller than the width of a human hair. 

Curiosity also has the ability to get its “hands” dirty. It can pick up rock samples using its 7-foot (2-meter) arm or use its drill to collect powdered samples to test for organic molecules. As an interesting aside, Curiosity was the very first rover that could drill robotically on another planetary surface.

The rover is able to analyze its samples through X-ray fluorescence. That’s when X-rays are shot through the rocks, the rocks are agitated, and we can see how the chemicals are held together. Their crystalline structure tells us a lot about what’s going on in the rocks on the surface of Mars. 

Fortunately, the rover doesn’t need to sniff and touch every rock. Instead, it can fire its laser at the rocks, vaporize thin layers on the surface, and then analyze the released gasses. Those gasses allow it to make out the rock’s chemical composition and identify the elements it’s made of. 

To search for traces of water from a distance, Curiosity can bombard the surface with neutrons to determine if liquid or frozen water can be found underground. This works because water is made up of one part oxygen and two parts hydrogen. If the neutrons interact with any hydrogen atoms, they’ll slow down. So, Curiosity just releases the neutrons and stands by, looking out for any tell-tale signs of change.

Finally, while the rover moves along the surface, its environment monitoring system measures atmospheric pressure, temperature, humidity, winds, and ultraviolet radiation levels. Phew. Yeah, it's a lot.

10 years of Curiosity's discoveries

With all these tools in Curiosity's arsenal, it’s not surprising that the mobile lab has made a number of startling discoveries. 

In the first weeks after it landed, the rover's images helped its handlers make their first mission discovery. In a stroke of luck, Curiosity touched down in an area where water once coursed over the surface. 

On an outcrop named ​”Hotta,” after Hotta Lake in Canada, it found rounded pebbles mixed with hardened sand, evidence which indicated that a stream ran (quite vigorously!) long ago on the red planet. From the size of the gravel in the rocks, the water was estimated to be somewhere between ankle and hip deep, moving at a speed of 3 feet per second (0.9 m/s). 

This marked the first time we saw conclusive evidence of water-transported gravel on Mars, and it would become what NASA scientist John Grotzinger called the first direct evidence of a potentially habitable environment.

But it certainly would not be our last.

Curiosity then headed eastward, toward Yellowknife Bay. On the way, it drilled into a rock on an outcrop called “John Klein” and collected the first samples of materials ever drilled from rocks on Mars. Analysis of the sample revealed clay minerals, which is evidence of sustained liquid water that was not too acidic or salty (perhaps a lake?). 

Want to know something even more interesting? Grotzinger says that, if we were on the planet then, we would have been able to drink it. 

So, traces of water? Check. Sustained conditions favorable for life? Check. What about clues of microbial life?

On Earth, wherever there is liquid water, there is microbial life (things like viruses, some fungi, and related organisms too tiny to see). In fact, for most of Earth’s history, the only life was tiny microbes. And to this day, microbes make up most of the living matter on our planet. As a result, scientists expect that any life on Mars — if it ever existed — would have been microbial.

Remember Curiosity’s dig into the John Klein rock I mentioned earlier? Aside from a body of water, samples from the rock had the key chemical ingredients needed for life, including sulfur, nitrogen, hydrogen, oxygen, phosphorus, and carbon. And pairings of sulfates and sulfides in the mix could be a sign of an energy source for indigenous Martian life, such as microbes. 

In short, Curiosity gave us a part of what we were looking for: evidence that Mars could have supported microbial life. It’s not conclusive evidence of actual alien life, but it was a monumental breakthrough. And the findings don’t stop there.  

Over nearly a decade of exploration, 24 of the rock samples Curiosity collected across the Gale Crater hinted at signs of life. Specifically, the rocks were found to have organics i.e., carbon-containing molecules that are the building blocks of life on Earth. 

Teams also found that 10 of the samples had carbon-12, a smaller and lighter carbon isotope. On Earth, organisms use carbon-12 to metabolize food and photosynthesize. However, it’s unclear where the carbon enrichment is coming from on Mars. There are a couple of hypotheses — some involving life and others not.

For now, the question is unanswered. But Curiosity is still exploring the slopes of Mount Sharp for information. And in the coming years, it could find evidence of life…assuming it can keep going. 

The state of Curiosity 

At the time of writing, the rover has been on Mars for over 10 years — much longer than its original two-year mission plan. And unfortunately, it has received its fair share of bumps and bruises. Images of Curiosity in January 2022 showed wheels with holes and missing pieces, broken grousers (raised treads), long cracks, and bent metal. 

Such things should be expected when one is working year after year on an alien world, but how long can the rover keep going?

One way to answer this question is through energy. That’s what keeps the robot ticking along, after all. Curiosity is powered by an instrument that NASA calls the multi-mission radioisotope thermoelectric generator (MMRTG), In short, it’s nuclear powered. This device should be able to continue converting the heat of plutonium-238's radioactive decay into electricity for a long time. 

Grunsfeld’s prediction back in 2012? It has about 55 years of positive power margin.

Of course, that length is relatively unlikely. General wear and tear will get to it first. Opportunity lived on Mars for nearly 15 years. So, Curiosity likely has at least a few more years of exploration left in its wheels.