Curiosity’s first year on Mars: Pebbles and other profound things

What the Curiosity rover has told us about Mars and it’s Earth-like past.

Curiosity Mars Rover selfie
"It's worth stepping back for a minute to consider what Curiosity is," writes Ian O’Neill [NASA]

Curiosity’s first year on Mars was, surprisingly, far from being an alien experience.

On August 5, 2012, at 10:17 pm Pacific Time, the sophisticated six-wheeled NASA robot touched down inside Gale Crater near the Red Planet’s equator.

Using an ingenious “guided reentry” technique and applying a never-before-used rocket-powered “sky crane” to lower the rover the final few feet onto the surface meant that, despite travelling tens of millions of miles from Earth to Mars, NASA’s Jet Propulsion Laboratory scientists (JPL) could score a hole-in-one, setting the rover down in a tiny landing zone a short trek from its ultimate target, the 5.5 kilometre high peak in the centre of the crater, Aolis Mons (aka “Mount Sharp”).

The important thing to remember about Gale Crater is that it has a landscape like no other mission has seen. Sure, we’ve had missions on the Martian surface before, but until now, the red-infused dusty landscape has appeared anything but familiar.

That all changed when, on August 8, 2012, Curiosity beamed back a panoramic shot of the insides of Gale Crater; JPL scientists and the public alike were taken aback by how Earthly it looked. Even lead Mars Science Laboratory (MSL) scientist John Grotzinger quipped: “You would really be forgiven for thinking that NASA was trying to pull a fast one on you and we actually put a rover out in the Mojave Desert and took a picture, a little LA smog coming in there,” during the August 8 mission press conference.

He wasn’t wrong – the view showed a black and white panorama of Gale Crater’s distant rim slightly obscured by misty air with a rock-strewn plain extending into the distance. It could have been a black and white photograph of the Mojave Desert just before the Gold Rush in the mid-1800s.

But this wouldn’t be the only discovery that, over the next 12 months, would draw Earth-like comparisons.

Volcanic rock

Soon after landing inside Gale Crater – the site of which was nicknamed “Bradbury Landing” after the recently deceased sci-fi author Ray Bradbury – Curiosity began the lengthy process of testing out all its instrumentation. The first target for Curiosity’s famous laser-firing Chemistry and Camera (ChemCam) instrument (located at the end of the rover’s mast, resembling a boxy “head”) was a small football-sized rock jutting out from the dusty surface. It was unremarkable (apart from its uncanny pyramidal shape), but it was soon to become very remarkable as being the first ever Martian rock – indeed any extraterrestrial rock – to be laser-blasted by a man made robot.

Curiosity drills into rocks at Yellowknife Bay  [NASA]

The intent of burning laser holes into rock wasn’t part of NASA’s “shock and awe” campaign of Martian domination; it was to remotely analyse the minerals contained within that rock. The laser rapidly fires short, powerful bursts into the rock, blasting out little divots. The rapid formation of plasma from the rocky material generates a vapour that can then be analysed by the ChemCam camera.

The rock – nicknamed “Jake Matijevic” after the NASA engineer who sadly died in the same month Curiosity touched down – ended up revealing some fascinating history behind its formation and the chemistry it contained. Not only was it an igneous rock (ie it solidified from volcanic processes in Mars’ ancient past), it was “a very close match to highly crystallized, or fractioned magmas, that occur in particular places on Earth”, reported geologist Edward Stolper, of the California Institute of Technology (Caltech), during an October 2012 press conference (it turns out the formation of these kinds of rocks is analogous to how colonists used to ferment hard cider, but that’s another story ).

On analysing some Mars soil (known as regolith) with its Chemistry and Mineralogy (CheMin) instrument, Curiosity also revealed its volcanic nature, discovering that it had a very Hawaii-like flavour (in a mineralogy sense). This was another “first” – the x-ray diffraction technique had never been carried out on Mars before.

Powerful mobile geology laboratory

It’s worth stepping back for a minute to consider what Curiosity is. Curiosity is kitted out with 17 cameras, all designed with specific tasks in mind. The rover also has a drill to excavate material from rocks. It also has a sample retrieval system that can drop powdered material into its onboard chemistry laboratory. Add these factors to the fact this car-sized robot can move, fire a laser, is powered by radioactive pellets and we have a powerful mobile geology laboratory that can look for interesting things, sample them and analyse them.

Science involves observation, formulating theories, analysis, testing, further observations and more analysis. Usually these things are done by humans, but in the case of Mars, we’ve had to send a robot as our science emissary. Curiosity is the most advanced rover ever landed on another world and it oversees the scientific process as diligently as its human counterparts on Earth programmed it (of course, Curiosity cannot think for itself, although many functions are automated – that’s left to the scientists and engineers on Earth).

So, not only does Gale Crater look like the Mojave Desert on a smoggy day, a rock found on the ground and the grains in the regolith were formed in a similar way to igneous rocks on Earth. But what other discoveries gave scientists a pang of deja vu?

The key mission objective for Curiosity is to seek out past (and, potentially, present) habitability on Mars. Habitability asks the question: could the Martian environment have allowed life to gain a foothold at any time in its history?

The Martian surface, by its nature, is generally hostile to life (as we know it). It is many times more arid than the driest desert on Earth; atmospheric conditions are frozen and hostile; radiation levels are high; poisonous chemicals (known as perchlorates) are laced with the regolith. In short, there are few obvious places for even the most hardy of bacteria to hide. And yet Curiosity hit the mother lode even before it rolled its first metre – it had landed on an ancient riverbed. Devoid of water for millions of years, this at least provided evidence that Mars wasn’t always this barren; it had flowing water feet deep!

This brings me to the pebbles.

Pebbles on Mars

Soon after touching down, Curiosity took a series of high-resolution photos of the landscape surrounding Bradbury Landing. In those first pictures were sedimentary rocks we commonly find on Earth. These rocks contained many smaller rounded rocks of all sizes, suggesting these were conglomerates. On Earth, conglomerates are formed in river beds when water deposits material downstream. Rocks become eroded by fluvial action, creating pebbles. Eventually, these materials cement together creating sedimentary rock. The fact that these rock types can be seen on the Mars surface was strong evidence for vast quantities of water having flowed across the bottom of Gale Crater in the past.

This set of images compares the Link outcrop of rocks on Mars (left) with similar rocks seen on Earth (right)  [NASA]

But Curiosity, being the full-service geologist it was designed to be, carried out some in-depth studies on a rocky outcrop at “Yellowknife Bay” in the hope of supporting the observational evidence of an ancient riverbed. Spotting bright veins of material passing through the rock, mission scientists commanded Curiosity to look closer. After drilling into the rock and extracting the powdered material, Curiosity gave it the full laboratory treatment.

Just as suspected, the bright veins contained calcium sulphate, also known as gypsum, a mineral that is only formed through the presence of water. This discovery supported earlier observational evidence of gypsum veins uncovered by NASA’s veteran Mars Exploration Rover Opportunity that continues to explore the other side of the planet after nearly a decade on the Martian surface.

Of course, we knew that water exists on the surface of modern Mars before Curiosity landed on the Red Planet, but the rover has probed deeper, surpassing our wildest expectations for its first year on Mars. Not only has it identified rocks that formed via familiar geological processes, it landed at the bottom of a dry riverbed, confirmed by the presence of pebbles and conglomerates. Then it drilled in and uncovered wonderful chemical evidence of minerals that could only have formed in the presence of long-duration water.

Also moonlighting as a meteorologist, Curiosity determined that in Mars’ ancient past, the planet was a very different place – it had a thick atmosphere and played host to large volumes of liquid surface water. These are all indicators of a very habitable past Mars when Earth was only just emerging from a hellish ball of magma.

Curiosity will continue to hunt down Mars’ watery history and, perhaps, jump hot on the tail of organic chemistry. Unfortunately, Curiosity will unlikely reveal strong, direct evidence for past (or indeed present) microbial life in the Martian dirt – that will have to wait until Curiosity has done the groundwork, justifying a life-hunting mission in the not too distant future.

Ian O’Neill is Space Science Producer for Discovery News. He is also the founder and editor of space blog Astroengine.

Follow him on Twitter: @astroengine