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The Curiosity rover is carrying on NASA’s mission to find out what Mars is really like. In particular, it aims to discover if there really was life on the Red Planet. And recent revelations from its surface have proved exciting, as they reveal that the truth may be more astonishing than scientists had ever imagined.

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Curiosity is a part of NASA’s Mars Exploration Program. Its aim is to send scientific equipment to the planet and keep up a non-stop flow of discoveries and information. To do that, it is deploying a whole suite of robot landers, orbiters and labs that are joined to each other by a powerful network of communications.

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Curiosity has been on Mars since August 2012 – trying to answer a single question. According to NASA, it aims to discover, “Did Mars ever have the right environmental conditions to support small life forms called microbes?” Not long after it had arrived, the rover confirmed that there was evidence of places there that might once have supported life. And today, it continues to look at rocks old enough to provide more of that proof.

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The rover – which is about the size of a car – was intended to explore Mars’ Gale crater. Its landing site was about a mile and a half away from the point that NASA had aimed it at – not bad after flying 350 million miles. At first intended to explore the geology and climate of Mars for a couple of years, its mission was expanded after a year or so. However, at the time of writing, it has been working for more than seven years now.

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NASA conducted a contest with U.S. students nationwide to find a name for its rover. It received more than 9,000 suggestions, and from those, it chose Curiosity. This was the brainchild of then-sixth-grader Clara Ma. The girl from Lenexa, Kansas, was rewarded by being taken to sign the rover in NASA’s rocket workshop in Pasadena, California.

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Ma wrote in her submission, “Curiosity is an everlasting flame that burns in everyone’s mind. It makes me get out of bed in the morning and wonder what surprises life will throw at me that day. Curiosity is such a powerful force. Without it, we wouldn’t be who we are today. Curiosity is the passion that drives us through our everyday lives. We have become explorers and scientists with our need to ask questions and to wonder.”

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Among the objectives of Curiosity was to take a look at whether the area inside the Gale crater might ever have provided an environment for microbes to have survived in. And a year in, having discovered some possibility of the answer to that question being yes, it started to investigate whether life may have left traces by developing models to predict what would remain of it.

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The near-2,000-pound rover is about nine-and-a-half feet long and nine feet wide. Just like the Viking vessels – which landed on Mars in the 1970s – it gets its power from a radioisotope thermoelectric generator. In this system, a radioactive isotope, for example plutonium-238, decays and produces heat – which is then turned into electricity by thermocouples.

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Curiosity has six wheels and a rocker-bogie suspension that did double duty as the rover’s landing gear. The wheels are cleated and set up so that they can get the rover up a sand dune. Curiosity can literally turn on a dime and can roll over rocks that are a couple feet tall. It’s not the quickest though – moving about 200 yards or so a day.

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The rover picks out items that are of interest by using cameras that provide high resolution. If its interest is piqued, it can then vaporize a bit of what it sees using an infrared laser – examining the outcome to see what the rock it blasted was made of. If that is of further interest, it can then take a physical sample.

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Curiosity is the latest in a line of robot rovers that have gone to the Red Planet. The Mars Pathfinder mission sent Sojourner there in 1997, and it was followed by Spirit and Opportunity from a later mission. Curiosity is bigger than those rovers, and it’s jampacked with equipment so that it can explore an area that some have likened to the Four Corners area of the U.S. west.

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The mission took off from Earth for its ten-month journey in November 2011. It left Cape Canaveral Air Force Station riding on the back of an Atlas V rocket. This type of projectile has had an incredible success rate – with 81 of its 82 launches passing off without any hitch.

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The site where Curiosity came down was dubbed Bradbury Landing. This was named after science fiction writer Ray Bradbury – who passed away shortly before the rover touched Mars. It left this site fairly soon after arriving so that it could explore the Gale crater, and orbiters show that the wind is slowly eroding the marks of its landing.

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The crater features a mountain – Aeolis Mons or Mount Sharp – that Curiosity will take a look at. The plan was to land the rover anywhere within a 12-mile by four-mile ellipse that is near the mountain. Experts chose the site because it features material that has fallen down from the inside of the crater. It also has rock not investigated elsewhere on Mars – possibly having once been the bed of a lake.

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A nearby outcropping of rock caught the attention of the scientists working on the mission. It suggests that water once upon a time rushed past it as part of an ancient stream. And at the edge of the ellipse, there are signs of both sulfates and clays – both of which are good at sheltering the organic compounds that could indicate past life.

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Nowadays, it’s accepted that Mars probably once had liquid water, but that’s only because of Curiosity. In 2013 it found an area of gravel that scientists believed was once the bed of a stream. It later confirmed that Gale is likely to be the bottom of an ancient lake. Furthermore, there are even hints that water may still be found on Mars.

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Curiosity has also found that Mars might once have been home to life. In the cores it has taken from bedrock are the very elements that you’d need to build DNA. This at least shows that Mars once had the right conditions for life, as NASA spokesman Michael Meyer explained. He told the organization in 2013, “A fundamental question for this mission is whether Mars could have supported a habitable environment. From what we know now, the answer is yes.”

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But that’s not the only thing Curiosity discovered; it also found boron when it started up the mountain. Judging from the Earth’s own deposits of boron in deserts, scientists believe that the mineral was laid down by evaporation. This implies that it was once in a solution with water at a temperature above freezing, which would at least be warm enough for life.

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The rover has also been measuring changing levels of the gas methane. It hasn’t been found in large amounts, but its presence does prompt questions. Although it’s produced on some planets and satellites as an outcome of geology, on Earth it’s largely caused by living things – famously as cow farts. It probably doesn’t mean Mars has cows, but it could be the exhaust of microbes.

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In 2018 Curiosity came up with stunning proof that Mars does contain materials that form part of life. These organics include methylthiophenes and methanethiol – which have gotten NASA quite excited. Spokesman Thomas Zurbuchen said, “With these new findings, Mars is telling us to stay the course and keep searching for evidence of life.”

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Gale is the crater left by a meteor that hit Mars somewhere between three-and-a-half and 3.8 billion years in the past. As we noted, it was thought to have formed the bed of a lake. Curiosity has shown that this is very likely true, and not only that, but NASA has found signs of water all over Mars.

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Previous rovers and the orbiters that have circled Mars have seen signs of water – so much so that some scientists have posited that the planet once had oceans. The water vanished from the surface of Mars when it lost its atmosphere. However, pockets of brine close to the surface could well have survived – alongside deeper aquifers.

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If the high-salt puddles do exist on Mars, bacteria within them may have resisted becoming totally dry. Given that life is everywhere on Earth that you find water, the search for living things on Mars has focused on potential sites of liquid. However, that must be fairly well hidden because the thin, cold air of the Red Planet does not allow water to last long on its surface.

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However, as frost evaporates on Mars in the leadup to dawn, scientists say that humidity can hit as high as 100 percent. This would mean that Mars could – albeit briefly – resemble Chile’s Atacama Desert. This is Earth’s driest spot, but it does harbor life. And if the right salts exist on Mars’ surface, they could soak up the pre-dawn moisture. As a result, this could create fluids that stay liquid at lower temperatures and maintain microbes.

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But the humidity does drop during the day as Mars gets warmer. So anything that does live in the briny puddles would have to be able to live through being dried out each day. However, experiments with bacteria from salty areas of the Earth have shown that this kind of drying out can be withstood to some extent.

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Mark Schneegurt, who is an astrobiologist at Wichita State University in Kansas, told Space.com that scientists may need to change their views on what’s considered livable. This also means that they have to reconsider what’s safe in terms of microbes that could be carried from Earth. The next step for researchers is to look at whether the salt-tolerant microbes on our planet can also withstand the kind of cold that they’d experience on Mars.

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Furthermore, there’s some evidence that beneath a glacier on Mars lies a salty lake, and it may be possible that some sort of life could be surviving there. However, even if there are microbes that can survive, anything bigger remains extremely unlikely – it just couldn’t find enough to eat.

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But it’s definitely possible that microbes could be living in the water on Mars. After all, they exist on Earth in extremely salty conditions in large numbers. Some are also very hardy and able to survive without oxygen. What would be difficult for the tiny lifeforms to overcome, however, would be the deep freeze of Mars. But some microbes survive freezing to colder temperatures, and the salts that may exist on the Red Planet may even prevent the brines from freezing at all.

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In 2019 Curiosity came up with some exciting new evidence about the lake that may once have filled the Gale crater. Salts that it found are completely new and have not been found anywhere else on Mars. Researchers believe that these are minerals that made the crater’s sea salty billions of years ago.

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The sulfates suggest that exactly the kind of brines that are thought to be possible homes for microbes could have existed on Mars in the past. These compounds contain magnesium along with calcium and could have derived from basalts – which would lead to soils that are rich in the sulfates and chlorides but low in iron.

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Satellites that have observed Mars have led scientists to believe that in the deep past – in a time called the Hesperian period – the climate may have changed. And this, in turn, left a significantly more arid planet. Researchers wrote in the journal Nature in 2019, “The relatively low solubility of calcium sulfate minerals results in their widespread production during evaporation, while less common magnesium sulfate and chloride minerals represent terminal evaporation.”

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There are further implications too, because the sulfates were found in separate sections. It could perhaps mean that the brines that shelter life had come into being as the lake dried up. The researchers noted that there was the “potential for segmentation of the Gale lake into discrete ponds, including those where extremely evapo-concentrated brines might form.”

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In May 2019 the rover took a selfie of itself drilling samples at bits of rock named “Kilmarie” and “Aberlady.” Samples from these spots contained the most clay minerals yet found by Curiosity. This went to show that the area that the rover is looking at merits the name that scientists have given it: the “clay-bearing unit.”

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The massive amounts of clay are considered proof that lots of water did once lie in the Gale crater, but beyond that scientists are not certain of what they show. They think that mud from the areas of water formed rocks, and the clay itself is an outcome of a reaction of H20 and sediment.

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But as the rover climbs the mountain, things should become clearer. If sulfates are found higher up, this could mean that the rocks were formed in cycles or episodes of desiccation and rehydration. However, if they taper out, this would suggest that there was just one epic drying of the Gale lake along with the rest of Mars.

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Nevertheless, the water may not have completely dried out on Mars. If brine exists just below the surface of the planet, it may have captured dissolved oxygen. And that may still sustain microbes today. Research scientist Vlada Stamenković explained to Space.com in 2019, “[There] is so much more work still needed to better understand the martian habitability. I hope this creates excitement in the [scientific] community – in the world – to think of Mars as a potential place for life to exist maybe even today.”

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And there’s even a hint that life may well exist. Some of the scientists looking at Mars believe that recurring slope lineae – dark areas that come and go seasonally – may be caused by the brines as they escape from under the ground. Stamenković and his team have made models of how much oxygen the brines they believe are trapped under the surface might hold.

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Those models created by the team may also be reflected in results returned by Curiosity. That’s because it has discovered spied manganese oxides in the crater. Stamenković explained to Space.com that these oxides need a lot of oxygen to create. Indeed, on Earth, they only came into existence after oxygen began to stay in the atmosphere after an episode two-and-a-half billion years ago known as the Great Oxygenation Event (GOE).

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Stamenković explained that the manganese oxides were a sure sign of the kind of environment that could sustain life. He said, “Our model says that [manganese oxide formation] is possible to occur on Mars, because of the briny environment and the low temperatures.”

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There could be no GOE on Mars because it’s connected to photosynthesis, and the planet only has relatively little oxygen because it lacks plant life. Even so, some could have been trapped in the brines. And they may have joined by more oxygen from water molecules broken apart by radiation from the radioactive elements in the rocks found there. So, all the things needed for life may exist just beneath the planet’s surface, and the search is very much on for life on Mars.

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