Chapter 1: What is the significance of water on Mars?
When a private eye in a rain-hammered city wants to unravel a web of crime and corruption, they often have one mantra. Follow the money. In a trail of dollar signs, ones and zeros, provided they are dogged enough, they usually find the perpetrator. When it comes to the planet Mars, scientists have a different mantra. Follow the water.
The case they're trying to crack is one of the coldest cases on the books. One that has baffled investigators for hundreds, if not thousands of years. Did life ever arise on Mars? And like all good investigations, it's all about collecting the right evidence. If water did once flow on Mars... Signatures of life could be found in its sediments. Find the water, potentially find signs of life.
It's a good thing then that science has set to work detective with steel in their hearts, who rarely sleep, and whose memories are literally photographic. Rovers. And today we're going to look at the times they blew this water case wide open. I'm Alex McColgan and you're watching Astrum. Join me in this gritty supercut, because Mars is covered in a lot of grit.
For the moment, Mars rovers have proven once and for all that water used to flow on the Martian surface. It's quite the story. Just don't expect a femme fatale. There have been six successful rover missions on Mars, but of those we're going to focus on three. NASA's Opportunity and Perseverance rovers, and China's Zurong.
So, let's take a closer look at the first of our three rovers, going back to about halfway through its mission.
The date is the 15th of December 2010. 2,449 souls in Opportunity's mission to find evidence of past oceans on Mars. Up until this point, Opportunity had travelled over 25km, investigating rocks, craters and bedrock, while traversing sand dunes and plains.
The areas it had explored so far contained clues that suggested that these areas were regularly flooded by water, although it fell short of confirming that a constant body of water was present there, like an ocean.
Opportunity was now looking for something more definitive.
Mars' harsh environment had also started to take a toll on Opportunity, with some onboard motors failing, meaning it couldn't stow its robotic arm away anymore. Our persevering champion had just arrived at Santa Maria crater.
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Chapter 2: How have Mars rovers contributed to our understanding of water?
They named this vein the Homestake Deposit, and it likely formed from water dissolving calcium out of volcanic rocks, which combined with sulfur, and was then deposited as calcium sulfate into an underground fracture that later became exposed at the surface. The impact that threw Tisdale to likely had something to do with this vein as well.
If this is the case, it shows that water once flowed through underground fractures on Mars. Later analysis of the data Opportunity collected showed that not only was this likely to be gypsum, but also that the water here would have been much less acidic than it would have been around other locations on the planet, meaning it could have been more conducive to life.
Martian winter was soon setting in, meaning shorter days and a lower sun in the sky.
For a solar-powered rover that can't adjust the angle of its solar panels, this is not the ideal situation, but for the first time since the mission began, Opportunity had the opportunity to spend the winter on a slope aimed towards the sun, meaning that for this winter it would be confined to an area named Greeley Haven.
This area was not only aimed towards the sun, but it was also rocky, meaning Opportunity had a lot it could examine during these few months. This 360-degree panorama shows the tracks of Opportunity as it carefully navigated its way to its winter lodgings. Months had passed, and winter was turning again to summer.
On Sol 2947, Opportunity moved again for the first time since it set up camp in Greeley Haven. Luckily, everything that was functioning from before seemed to still be functioning, an opportunity headed out to the next point of interest. MOR data suggested clays were present in this area, and the mission team were determined to find it.
A beckoning outcrop was spotted around Sol 3057, and the microscopic camera revealed something about it that no one was expecting. Much like Opportunity's landing site, these smooth polished blueberry rocks were observed. However, this time they were very much a part of the rock.
They were also smaller than what Opportunity had seen before, only a few millimetres in diameter, and not rich in iron like the landing site blueberries. A few of the exposed blueberries observed had been eroded away, revealing their internal structure. Scientists described these blueberries as crunchy on the outside and softer in the middle.
They are different in concentration, they are different in structure, they are different in composition, they are different in distribution. It was quite the mystery. Opportunity had just one more place to visit on its trip around Cape York, and that was the clay patch dubbed Whitewater Lake.
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Chapter 3: What discoveries did the Opportunity rover make about past water on Mars?
While this might initially seem to be bad news, you might correctly conclude that not much life could be found in magma, scientists could discern signs of water erosion on the rocks. The ridges at the ends of the crater showed signs of water motion. Whatever volcanic activity had happened here, the water that created Jezero's delta must have come after it had already cooled.
As such, the presence of igneous rocks was actually good news. Igneous rock is usually very high in minerals. This is why the areas around volcanoes are so fertile. The presence of water and high mineral count rocks could have been the perfect conditions for life.
In the future, scientists will be able to send missions to locations like the Jezero crater delta as they make future attempts to locate alien life. Indeed, once humans land on Mars as is planned for the 2030s, it's not unimaginable
that archaeological dig sites will be one day set up in locations like this, with humans in spacesuits gently brushing away the fine oxidised iron and basalt rock to see if signs of life can be found underneath. But still, scientists yearned for clearer pictures of Mars' ancient waterscapes than this, and it was now likely that water had pooled in craters and flowed in rivers.
But what about the step beyond that? Could ancient Mars have once housed oceans? If true, this would be exciting for those searching for signs of ancient alien life. A shoreline could have supported an abundance of life, possibly entire diverse ecosystems.
And they might have left behind biosignatures, like scavenger hunt clues we can use to paint a picture of Mars' ancient coastal habitats. Shore environments offer key advantages to budding life. They concentrate organic molecules through evaporation, promote the formation of complex molecules like RNA and protein,
and provide mineral-rich surfaces and energy sources like UV radiation, heat, and chemical gradients, all of which can drive the chemistry needed for life to arise. In contrast, rivers are too dynamic and dilute to support the delicate chemical conditions needed for life to arise.
They constantly flush materials downstream, making it difficult for molecules to accumulate and react the way they need to to form life. So if researchers could find evidence of a standing body of water on Mars, like a lake or an ocean, they'd be in a much better spot to search for remnants of microbial life.
The Chinese Tianwen-1 mission might have captured the most compelling evidence yet for ancient oceans on Mars.
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Chapter 4: How did the Perseverance rover explore the Jezero crater?
All 76 of the geological reflectors they encountered sloped in the same direction at an angle between 6 and 20 degrees. Putting the pieces together, the team realised that 10 to 35 metres below the planet's surface lies a 1.3 kilometre stretch of terrain sloping towards the lowlands. It seemed like more than coincidence.
Could this be proof of what they were looking for, the indisputable evidence for an ancient shoreline on Mars? The team hurried to compare this Martian picture to the buried beaches found on Earth, and found the Bay of Bengal to be such a strikingly similar Earth analogue, they even featured this finding in their paper.
One of the co-authors of the original research paper that published the findings said that It's a simple structure, but it tells you there had to be waves, there had to be a nearby river supplying sediment, and all these things had to be active for some extended period of time.
We also know that the Sun and Mars' bigger moon Phobos do affect the planet's surface gravity, which could have caused tides on the ancient ocean. The team briefly considered, but ultimately ruled out other possible explanations for the sloping structures. They argued both.
Sand dunes and lava flows would lead to slopes pointing in multiple directions, yet in the Tsurong data, all the reflectors point the same way. They concluded that these slopes were more consistent with a coastal foreshore environment, strengthening the case that Mars once had dynamic shorelines that experienced tides, wind and waves, just like Earth does today.
For decades, scientists have been locked in heated debate over the question of Mars' oceans. The evidence seemed frustratingly unclear, prominent researchers dismissed shoreline evidence as artefacts or poor image resolution, and climate modellers struggled to explain how liquid water could exist on an early Mars with a fainter sun.
You see, 3.5 billion years ago, our sun was about 25% dimmer than it is now, too faint to keep Mars above freezing. And yet, our climate models predict that at the time, Mars would have been covered in rivers, lakes, and even oceans. This leads to what is known as the faint young sun paradox. If the heat for liquid water didn't come from the sun, it must have come from Mars' atmosphere.
This has led to three theories trying to solve the faint young sun paradox. The first says Mars was warm and wet. The idea is that Mars' atmosphere was loaded with greenhouse gases, mainly carbon dioxide and water vapour, which made it so dense it could trap enough heat to allow liquid water to persist for millions of years. This would explain the evidence pointing to rainfall, lakes, and oceans.
But the problem is, according to our models, carbon dioxide and water vapour alone can't produce the warming needed for this scenario. Other gases like methane, ammonia, or hydrogen would be needed, but they are unstable and hard to maintain long term.
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