1. A rough start

The obsession to get to the red planet has been strong for decades. The United States, the European Union, and the USSR/Russia have been reaching for the stars since the 1970s. The USA’s NASA and Russia’s Roscosmos have been working hard, frequently in competition, sending landers and probes to the surface of Mars.

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In 1971, Mars 2 and Mars 3 orbiters deployed a pair of landing craft down to the Martian surface. The Soviet landers never managed to fulfill their duties, however, as Mars 2 lost contact during entry and crashed into the surface, and Mars 3 landed and lost touch with mission control after 20 seconds.

2. Success at last

After another failed Soviet Mars lander mission (Mars 6), NASA’s Viking 1 and Viking 2 landers successfully touched down on the Martian surface. They sent back the first photos of the Red Planet, albeit in black and white, and collected the first soil samples for testing. The Viking missions were a triumph for planetary exploration.

NASA

The first successful Mars rover was Sojourner, which arrived on the Red Planet in 1997 and transmitted data, including color photos, back to Earth for 85 days. Sojourner long outlived its expected lifespan and set a strong precedent for other rovers that would soon arrive in the next few decades.

3. Roving the surface

After Sojourner‘s arrival on Mars, it was joined by several other landers. Of all the newcomers, only one of them managed to land on the surface and set out on its mission. For nearly a decade, Sojourner was the last set of wheels to roam the surface of Mars, but its successors would later surpass even this great technological accomplishment.

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It wasn’t until 2004 when the twin rovers Spirit and Opportunity were launched that another set of wheels arrived on Martian soil. They drew the spotlight with their tandem discoveries until a new player arrived. In 2012, the Curiosity rover touched down and began its historic journey of Martian research.

4. Such a lonely place

Currently, Curiosity and Opportunity are the only two active probes on Mars. Spirit was declared inactive in May of 2010 after numerous failed attempts to communicate with the rover. All three of the rovers are spread out across the planet’s surface, with the two operating ones on opposite ends of the globe.

NASA

Opportunity has been quiet since the summer of 2018 when planet-wide dust storms presumably covered the bot’s solar panels. NASA hopes winds in the following season will clear the arrays and allow the rover to recharge. The rover has recovered after going quiet before, and scientists remain hopeful that its mechanics will prove durable once again.

5. Curioser and curioser

Meanwhile, Curiosity continues to pursue its mission. As a leading member of the Mars Exploration Program, Curiosity has a crucial job to do, and it’s been working tirelessly since 2012 to send critical data back to Earth for NASA’s scientists to analyze. While it’s photographs are most popular, its technical data has been invaluable.

NASA

The Mars Science Laboratory, which is the mission Curiosity is a key part of, has eight primary objectives. The car-sized rover is equipped with outfitted with an advanced array of tools to help it complete these tasks. Some of those tools even come in handy when it’s time for the rover’s lonely little birthday celebration.

6. Learning how Mars came to be

Based on clues from satellite imagery, scientists studying Mars have reason to believe that the Red Planet once had an atmosphere similar to Earth’s and a similarly wet climate to match. One of the duties assigned to Curiosity is studying surface conditions and rock samples to learn more about that past life and what happened to it during the last 4-billion years.

NASA

In addition to looking at Mars’ past, Curiosity is in charge of studying the atmosphere’s present state, as well as the magnetic field (or lack thereof) that would keep an atmosphere in place. Of its duties, the study of how water and carbon dioxide have historically cycled on the planet is one of the most newsworthy pursuits. After all, water is one of the first places we know to look for familiar forms of life.

7. Studying rocks and singing to itself

Curiosity spends a lot of time looking at dirt. It also enjoys long afternoon strolls along the edges of craters picking up rocks. As ridiculous as it sounds, geological analysis of Martian soil and other deposits is what our little rover spends most of its time doing. Its chassis is equipped with state-of-the-art tools that break down and perform chemical analyses on surface and sub-surface materials.

NASA

This advanced set of soil analysis hardware is also used once a year, on August 6, to play the solar system’s loneliest rendition of “Happy Birthday.” The rest of the year, Curiosity works hard to uncover Mars’ geological history. By studying trace minerals in the red dust and rock, we can learn what processes occurred and shaped the planet’s surface, from volcanic events to space debris impacts.

8. Roasting in radiation?

The lack of a significant atmosphere and magnetic field around Mars means that the planet’s surface is continually being bombarded with radiation. Solar events hurl all kinds of radiation at Mars in addition to galactic and cosmic radiation endemic to interplanetary space, posing a problem for would-be future human residents.

NASA

Curiosity has been measuring radiation levels all the way since Earth. Monitoring onboard levels during the flight between the two planets provided NASA with crucial information for use in future manned missions to the Red Planet. Similarly important are the rover’s ongoing measurements of surface radiation as it roams across the ruddy terrain.

9. Biology on another world

Of all the points of study that Curiosity has been tasked with, the ones most exciting to scientists and enthusiasts alike are the ongoing reports of Mars’ biosphere. Chemical analyses of the rocks and soil reveal organic carbon compounds similar to ones found on Earth. In addition to carbon, the tests also look for hydrogen, nitrogen, oxygen, phosphorus, and sulfur, which make up the building blocks of carbon-based life.

NASA

While looking for signs of present-day life, the rover is also keeping a keen eye out for signs of ancient biology. Biosignatures and biomolecules are evidence that life may have once existed on Mars. About a year into the mission, NASA determined that there was enough supporting evidence to conclude that ancient Mars could have sustained life. A ninth objective was then added to Curiosity‘s mission, involving the study of predicting how archaic life might have been preserved and how it decayed over time.

10. Treasure hunting

Finding water on Mars, solid or liquid, has been one of the most prominent adventures in the Mars excursion for over a decade. Water holds may of the keys to life as we know it, and it was where evolution began for us. Primordial seas of component materials gave rise to the earliest-known creatures on Earth.

NASA

If water could be located on Mars, we thought we’d be one huge step closer to learning where we came from and maybe finding out that we weren’t alone in the universe. The planet’s two polar ice caps became focal points of the Mars Exploration Program. Mars might be too dry for liquid water to stick around, but maybe frozen water would have a chance.

11. Fool’s gold

When we finally reached the ice caps, our rover started digging. There was some disappointment when initial results showed that the poles were covered in frozen carbon dioxide, or “dry ice.” Although it wasn’t water, the composition of the poles was still a monumental discovery.

NASA

While the deposits provided valuable information about the composition of what little atmosphere Mars had left, it wasn’t what we were hoping to find. After digging a little deeper, scientists realized that things might not have been so bad after all. Further analysis of the polar ice caps revealed that there wasn’t just dry ice at the poles, but frozen water as well.

12. Water on Mars

Both the northern and southern ice caps contain a mix of dry ice and water ice. What’s more interesting is the type of water ice found at the poles. Unlike the majority of water on Earth, which is composed of the lighter, more common isotope of hydrogen, protium, Mars’ ice is primarily made of “heavy water,” which contains the far rarer isotope, deuterium.

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The difference in water molecule composition seems to suggest that a massive amount of water evaporated from the surface of the planet at some point, leaving behind concentrated deuterium-ice. Based on current calculations, there was once enough water to cover about 20% of the surface in oceans up to a mile deep, assuming it had ever been in a liquid state.

13. Oceans of life?

As impressive as it would be to find seas of life anywhere else in the solar system, any living things that might still be around on Mars would be on a much smaller scale. On Earth, organisms called extremophiles set the course for our search for extraterrestrial life. They would also play a vital role in biological discovery on our neighboring planet.

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Extremophiles are typically microscopic organisms that can survive in harsh conditions that would kill most other living things. Environments of complete darkness, intense hot or cold, and extreme levels of radiation are all prime places to find these exceptional survivors, which is why Mars could be home to these resilient lifeforms.

14. Space hitchhikers

One type of extremophile we know can survive in the vacuum of space is tardigrades. Neither radiation nor the near-absolute zero temperatures can kill them. These microscopic creatures can dry out and put their bodily functions on pause until they can find water again, which is vital to their survival.

Wikipedia

While these creatures might be able to survive on Mars, there’s no doubt that they are from Earth and won’t be greeting our rovers any time soon. Their ability to survive in completely foreign environments might make them suitable candidates for future experiments. Also known as “water bears”, these little guys have proven their ability to even survive in the vacuum of space.

15. Starting small

Any traces of life — past or present — that we might find on Mars would be on the microbial level. Anything more advanced than that, and we would almost certainly have already seen traces of their existence. Because we are looking at the microscopic level, cross-contamination is important to rule out.

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Fortunately, the rovers were assembled in sterile laboratories to minimize the chances of contamination. In the absence of footprints or lakebed fossils of plant life, our rovers are busy magnifying rocks and inspecting layers for anything that resembles microorganisms and the patterns they may have left behind in the soil or underground.

16. Korolev crater

Speaking of lakebeds, photos of a magnificent discovery on the Martian terrain were recently published. Named the Korolev crater, it was identified not by NASA, but rather the European Space Agency. The ESA has a satellite of their own which not only takes high-resolution photos of the lunar surface, but is also able to detect emissions from the surface that may indicate life below ground.

Daily Mail

Located on the planet’s northern polar cap, the Korolev crater is an area of particular interest to scientists because of its abundance of ice, where below-ground microbes may be hiding. Evidence from orbiting satellites, rovers, and landers reveals ancient water sources like this one, and in vast quantities, the icy shell may house what researchers have been eager to prove: microbial life forms.

17. Lake of ice

The ESA has also called the crater a “cold trap,” because air moving over the crater is dramatically cooled down. Concerning the water composition on Mars according to Germany’s space agency, DLR: “There is no liquid water on Mars, but there is a considerable quantity of ice. The planet’s two polar caps consist of a mixture of carbon dioxide and water ice, which vary greatly in proportion to one another depending on the season.”

Daily Mail

The ESA’s spacecraft, Mars Express, flies over the terrain and takes photos of different strips of land at a time. These strips are sent back to Earth where researchers splice the photos together to create a complete image of the crater and other surface features. Unique lakes of ice like the one at Korolev are encouraging not only because we may discover organic material, but also that humans will have water to use for future missions.

18. Remnants of the past

Several times throughout Curiosity‘s journey, the rover has found what looked like bacterial fossils left imprinted on Martian rocks. Combing the soil for familiar patterns is difficult, but it’s the only way to be certain. Upon closer inspection, the earliest patterns that were uncovered turned out to be a false alarm.

NASA

Continuing its search, Curiosity resumed its quest of picking up geological samples and searching them for clues that could point towards life on Mars. The polar ice caps, where the only significant quantities of water have so far been found, are our best bet, as the ice could be home to a more thriving environment for organisms.

19. Clues from home

On Earth, scientists have frequently used our extreme climates to test their theories for space exploration. Some of our Mars rovers were tested in the deserts and lava flows in Eastern Idaho, where the terrain is similar to what scientists expected to find on Mars. Searching for life in unlikely places has also been an ongoing adventure here on our home planet.

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Microbes living deep underneath Antarctic ice provide insight into what Curiosity and future rovers might find hiding on Mars. The existence of these strange organisms in Earth’s most brutal habitats makes scientists hopeful that there could be similar life elsewhere in the planetary neighborhood.

20. Oops

As it turns out, NASA’s first successful Mars landers from back in the 70s, Viking 1 and Viking 2, were the first probes to hold organic matter on Mars. Nobody knew until decades later because the Vikings accidentally burnt it to a crisp. It wasn’t until Phoenix found traces of a powerfully volatile compound called perchlorate in the soil near the poles that scientists put two and two together.

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By that point, they knew Mars had abundant carbon, and they reasoned that the Viking mission’s method of testing the soil by lighting it on fire was what caused the problem. The perchlorate, which is an additive in rocket fuel and fireworks to increase the rate of combustion, caused the materials in the soil to burn so quickly that it vaporized the carbon before the landers could measure it.

21. Promising prospects

A byproduct of the reaction was later found in the ground near one of the Viking craft, confirming the suspicion. After finding organic carbon locked away in the Martian soil, the rovers doubled down in their search for the building blocks of life. Carbon was step one. Now, they had to find other elements.

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For carbon-based life as we have on Earth to develop, there are a few elemental basics that need to be in place. Carbon is a big one, but organic molecules also include hydrogen and usually oxygen, nitrogen, and sometimes other elements. All life on Earth is carbon-based, but scientists have speculated that extraterrestrial life could be silicon-based, for example.

22. Traces of hope

In the summer of 2018, Curiosity caused a stir among the scientific community when it sent back the first truly promising evidence for the existence of life on Mars. Nobody wanted to jump to conclusions, but as consistent data kept coming back, the anticipation amongst the scientific community had grown to excitement.

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The little rover had managed to find more than just trace amounts of organic molecules for the first time since Mars surface exploration began. Previously, rovers and landers had found organic compounds in such small traces that scientists couldn’t rule out the possibility of contamination. This time, the abundant samples were pointing toward some promising results.

23. A major breakthrough

With the discovery of significant deposits of organic compounds, Curiosity had unearthed something monumental. Hidden in three-billion-year-old sedimentary rocks on the Martian surface were hardy remnants of organic molecules, sending waves of jubilation through the space exploration community. Decades of scientific research and astrological engineering had yielded incredible results. The good news doesn’t stop there.

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In addition to the organic compounds, Curiosity detected seasonal fluctuations in methane levels as evidenced by soil samples. While the methane cycle could be caused by interactions between chemicals in the planet’s crust, scientists are hoping it’s evidence that microbial colonies are alive and thriving underneath the surface of the Red Planet.

24. Next-door neighbors?

Methane levels on Mars appear to rise in the summer and fall in the winter. As far as we’ve observed from microbial colonies on Earth, metabolic rates increase, to a point, with the temperature. As their environment cools, their metabolic rates decrease in kind. Fluctuations like these would explain how lifeforms might survive or behave in such an atmosphere.

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Current estimates place the reservoirs of methane deep underground where organic life might be churning away. What we don’t know is whether or not the gas is newly formed or if it has been around for a long time. Either way, the discovery points to a large, possibly living source that is the culprit behind the methane emissions.

25. Crystalline mysteries

One of NASA’s lead scientists believes that the underground methane is stored in ice-like crystals called clathrates that hold onto the gas, releasing it gradually as time goes on. When the methane reaches the upper layers and to the surface, it sticks to Martian dust and soil particles, leaving an elemental fingerprint of sorts.

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When it did, it left behind the traces that Curiosity was able to pick up, read, and analyze. According to the experts, the reservoirs of gas were likely either caused by naturally-occurring chemistry in the soil or by microbes. Currently, we don’t have enough evidence to rule out either possibility, but the data is compelling.

26. Keep searching

While we haven’t found proof that life does or did exist on the Red Planet, we have found evidence that says we’re on the right track to reaching a definitive conclusion. Measuring seasonal fluctuations in anything on Mars is a waiting game, as a single Martian year is equivalent to nearly two Earth years, and seasonal changes make for a slow process for new data collection.

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In 2020, Curiosity will gain some new companions, ones with more capability to analyze the fields of methane. This will hopefully find even more promising evidence of life outside of Earth’s atmosphere. Pursuing the methane lead is our best chance so far at finding out more about what once was or maybe still is living on Mars.

27. What we’ve learned

Curiosity‘s findings in the old Martian lakebed near Gale Crater have taught us one thing for sure. Although the oxidized surface of the Red Planet is too irradiated to let most things survive, drilling a few inches into the ground opens up a whole new world of possibilities. Just like Earth, there’s more to Mars than what’s on the surface.

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The discovery of organic compounds that are definitely of Martian origin has taught us something new about the persistence of these molecules in harsh environments. With a little bit of protection from radiation, these organics can be preserved for billions of years. And as old as our solar system is, we’re getting an ancient history lesson in the process.

28. Exploring the neighborhood

If the source of the methane — a primary greenhouse gas — turns out to be biological life, it will transform how we look at our place in the universe. Some of the gas giants’ moons are already considered to be candidates worthy of exploration in the name of finding life, but as with any interplanetary mission, we don’t always have the available resources for exploring every planet and moon.

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Should Mars turn out to be harboring microbes under its surface, the potential skyrockets for Io and Europa to be holding more secrets than we’d previously considered. We could finally have a sense of peace knowing that we aren’t the only life in the universe (and a great excuse to travel to the moons of Mars).

29. Going where no one has gone before

We know with a fair amount of certainty that prolific microbial life early in Earth’s history was responsible for constructing our atmosphere. The anaerobic bacteria of the time produced methane, oxygen, nitrogen, and other vital gases as waste. Once again, we are reminded that methane is a key piece of evidence in the search for life elsewhere in our own solar system.

Flickr — Kevin Gill

Terraforming may currently only be an exercise of science fiction, but if we learn that Mars can hold life, does it have to stay that way? Could we use gene splicing to create Mars-friendly microbes to produce greenhouse gases in ratios similar to those in our atmosphere? What about heating the planet to sustainable levels with nuclear energy?

30. Pipe dreams

As cool as it would be to terraform Mars, it’s highly unlikely. Reactions in the planet’s core eons ago caused the planetary magnetic field to disappear. Without that, Mars can’t hold in much of an atmosphere, and there’s nothing to protect the surface from dangerous radiation from our sun and other galactic sources.

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Our best bets for living on Mars are more along the lines of what Andy Weir proposed in The Martian. Habitation modules would be far less expensive and much faster to produce than a whole magnetic field and a planet-wide atmosphere. In other words, Matt Damon has already demonstrated what the Martian lifestyle would realistically be like.

31. But what if

That doesn’t mean people haven’t considered what it would take to get Mars back up and running. The cooling and slowing down of Mars’ core was what lost the magnetic field, so why not start it up again? Several different methods for how this could be done have been put forth.

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Speculation about “jump-starting” a planet has been more fanciful than factual, but some theorists in support of the idea claim it’s possible. One theory suggests that a series of nuclear detonations deep within the planet could be enough to get the ball rolling again, but the claims are sketchy at best.

32. Back to reality

Going forward, NASA plans to continue tracking the source of the methane and looking for other patterns and signs that could indicate life beneath the planet’s red surface. The countless lookalikes make this a difficult task, but the fact that we’ve already made headway is a promising suggestion that we are headed in the right direction and looking in the right places.

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Even if we don’t find life hiding in the dark, Curiosity and its friends have helped us learn so much about our next door neighbor. No matter what we discover from here on out, we’ll have a better sense of how our universe works and where we stand in it.