August 5 marks the fifth anniversary of the Curiosity rover’s 2012 landing on Mars. The little robot is by now an old pro at doing science on the Red Planet. And this Little Robot That Could has learned a lot.
Its mission had been simple. It was to look for signs that the planet might once have been habitable — for microbes, not for Matt Damon! To do that, NASA sent the robot to Gale Crater. It’s a huge impact basin with a mountain at its center. Curiosity has traveled across the crater, turning over rocks. Along the way, the robot collected evidence of ancient water, minerals, organic chemicals and other materials needed for life.
Curiosity was so successful that NASA has extended its mission through October 2018. After all, there’s still plenty of interesting chemistry and geology to be done. As the robot continues to climb Mount Sharp at the center of the crater, it will explore three new rock layers. One is dominated by an iron mineral known as hematite (HE-mah-tyte). Another layer is mostly clay. The third contains plenty of sulfate-based salts.
What more could Curiosity dig up over the next year? Here are four mysteries it might solve (or at least find more clues to).
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Are there remains of ancient life in the Martian soil?
Any signs of life would likely be microbial. Curiosity can take images of very tiny things with a tool known as the Mars Hand Lens Imager. To succeed at finding microfossils, however, those ancient cells would still have to be pretty big. What the rover might do instead is scan for the chemicals used to build such cells. And Curiosity can try that using its portable chemistry lab known as SAM (for Sample Analysis at Mars).
So far, SAM already has found a small organic molecule, meaning one with carbon in it. This ring-shaped chemical — chlorobenzene — turned up in ancient mud rock. Its discovery excited scientists. After all, chains of such molecules go into making things such as cell walls.
“We’ve only found simple organic molecules so far,” says Ashwin Vasavada. He works at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif. There, this planetary scientist heads Curiosity’s science team. Detective work in chemistry labs on Earth might point to whether bigger organic chemicals might degrade on Mars’ surface into smaller ones, such as chlorobenzene.
Curiosity might still turn up bigger molecules made from chains of carbon. The rover carries two sets of cups to do chemistry experiments. A set of dry cups contains chemicals that could draw out hard-to-find organic compounds. There are also “wet” cups. None of these have been used, so far. A December 2016 problem with Curiosity’s drill put the rover’s search for organics on temporary hold. Possible solutions are, however, in the works, NASA says.
How did Mars morph from wet and warm to cold and dry?
Studies have pointed to there once having been water on Mars. In fact, Gale crater once held a lake fed by rivers. Moreover, Curiosity’s very first drilling sample detected chemicals that can form only in nonacidic environments that would comfortable for Earth-type life. Among those chemicals was calcium sulfate. The rocks also contained clays. These would have formed in water — and only water that was slightly salty.
Scientists with NASA have concluded that the Martian soil seems the most hospitable environment ever detected outside Earth.
But things didn’t stay potentially cozy. Some 3.5 billion years ago, things changed.
The going theory is that when Mars lost its protective magnetic field, particles from the sun began stripping away some of the Red Planet’s atmosphere. (By the way, its atmosphere continues to erode today.) “That caused the climate to change from one that could support water at the surface to the dry planet it is today,” explains Vasavada.
Curiosity has turned up a relatively high proportion of heavy elements in the Martian atmosphere. This supports the idea that lighter elements were once there but simply proved the first to go.
There’s also a chance that as the rover hikes up Mount Sharp, it could capture regional evidence of the wet-to-dry transition in action. So far, Curiosity has investigated rocks from the end of the wet period. They pointed to the planet once having hosted surface lakes that lasted for millennia!
Rocky sites the rover is now approaching are younger. “Hopefully we’ll be able to get some insight by looking at these rocks into some of the global changes happening,” says Abigail Fraeman. She’s a research scientist at JPL. Probing rock at the new sites might help uncover what types of changes made surface lakes a thing of the past.
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Does Mars really have flowing water today?
Some mineral salts absorb water, then later release it as a liquid when they break down. The Curiosity team looked for the bursts of water that might result from such a process in Gale Crater. And it came up empty.
Two years ago, the Mars Reconnaissance Orbiter snapped images of shifting salt streaks. Those suggested Mars once had actively flowing water. These photos are the best evidence yet that Mars’ liquid water might not be gone forever.
Mount Sharp also has such dark streaks. Curiosity takes pictures of them now and again. “It’s something we keep an eye on,” Vasavada says. If the streaks change in a way that might indicate that they’re moving, the rover might drive over to look for water. Alas, so far the streaks have not changed.
What’s the source of methane in Mars’ atmosphere?
On Earth, microbes are big producers of methane gas. There is methane in the Martian air, too. But where it comes from is unclear. Atmospheric methane levels appear to vary over the course of a year. Changing temperatures or pressure might be behind these subtle fluctuations. Curiosity will continue to monitor methane levels. It also will collect more data, hoping to help pinpoint what’s behind the annual ups and downs.
At the end of 2014, scientists detected a 10-fold spike in the methane in Mars’ atmosphere. They now suspect that methane remains in the Martian air for only about 300 years. So, it’s a relatively new addition. “That doesn’t necessarily mean it’s being actively created,” Vasavada says. “It could be old methane being released from underground.” (As minerals interact with water underground, they sometimes help create methane gas.) Mars’ methane also might be the product of planetary dust particles as they break down on the planet’s surface.
Another possible explanation: Life! “We have zero information to know whether that’s happening on Mars, but we shouldn’t exclude [life] as an idea,” says Vasavada of methane-making microbes. Martian life is unlikely, he says, but it cannot be completely ruled out.
annual Adjective for something that happens every year.
atmosphere The envelope of gases surrounding Earth or another planet.
basin (in geology) A low-lying area, often below sea level. It collects water, which then deposits fine silt and other sediment on its bottom. Because it collects these materials, it’s sometimes referred to as a catchment or a drainage basin.
calcium A chemical element which is common in minerals of the Earth’s crust and in sea salt. It is also found in bone mineral and teeth, and can play a role in the movement of certain substances into and out of cells.
carbon The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemistry The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.
clay Fine-grained particles of soil that stick together and can be molded when wet. When fired under intense heat, clay can become hard and brittle. That’s why it’s used to fashion pottery and bricks.
climate The weather conditions that typically exist in one area, in general, or over a long period.
compound (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
crater A large, bowl-shaped cavity in the ground or on the surface of a planet or the moon. They are typically caused by an explosion or the impact of a meteorite or other celestial body. Such an impact is sometimes referred to as a cratering event.
degrade To break down into smaller, simpler materials — as when wood rots or as a flag that’s left outdoors in the weather will fray, fade and fall apart. (in chemistry) To break down a compound into smaller components.
element (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.
environment The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).
erode Gradual removal of soil or stone, caused by the flow of water or the movement of winds.
field An area of study, as in: Her field of research was biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.
fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.
geology The study of Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists. Planetary geology is the science of studying the same things about other planets.
habitable A place suitable for humans or other living things to comfortably dwell.
heavy element (to astronomers) Any element other than hydrogen (or possibly helium).
hematite A reddish-brown to black iron-based mineral, it’s the principle source of iron ore.
insight The ability to gain an accurate and deep understanding of a situation just by thinking about it, instead of working out a solution through experimentation.
iron A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.
lens (in optics) A curved piece of transparent material (such as glass) that bends incoming light in such a way as to focus it at a particular point in space. Or something, such as gravity, that can mimic some of the light bending attributes of a physical lens.
magnetic field An area of influence created by certain materials, called magnets, or by the movement of electric charges.
Mars The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.
methane A hydrocarbon with the chemical formula CH4 (meaning there are four hydrogen atoms bound to one carbon atom). It’s a natural constituent of what’s known as natural gas. It’s also emitted by decomposing plant material in wetlands and is belched out by cows and other ruminant livestock. From a climate perspective, methane is 20 times more potent than carbon dioxide is in trapping heat in Earth’s atmosphere, making it a very important greenhouse gas.
microbe Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
millennia (singular: millennium) Thousands of years.
mineral Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns).
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
monitor To test, sample or watch something, especially on a regular or ongoing basis.
NASA Short for the National Aeronautics and Space Administration. Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It also has sent research craft to study planets and other celestial objects in our solar system.
orbiter A spacecraft designed to go into orbit, especially one not intended to land.
organic (in chemistry) An adjective that indicates something is carbon-containing; a term that relates to the chemicals that make up living organisms.
particle A minute amount of something.
planet A celestial object that orbits a star, is big enough for gravity to have squashed it into a roundish ball and has cleared other objects out of the way in its orbital neighborhood. The solar system now includes eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
pressure Force applied uniformly over a surface, measured as force per unit of area.
proportion The amount of a certain component of a mixture relative to other components. For example, if a bag contains 2 apples and 3 oranges, the proportion of apples to oranges in the bag is 2 to 3.
propulsion The act or process of driving something forward, using a force. For instance, jet engines are one source of propulsion used for keeping airplanes aloft.
Red Planet A nickname for Mars.
robot A machine that can sense its environment, process information and respond with specific actions. Some robots can act without any human input, while others are guided by a human.
salt A compound made by combining an acid with a base (in a reaction that also creates water). The ocean contains many different salts — collectively called “sea salt.” Common table salt is a made of sodium and chlorine.
sulfate A family of chemical compounds that are related to sulfuric acid (H2SO4). Sulfates occur naturally in drinking water.
sun The star at the center of Earth’s solar system. It’s an average size star about 26,000 light-years from the center of the Milky Way galaxy. Also a term for any sunlike star.