Finding living Martians just got a bit more believable | Science News for Students

Finding living Martians just got a bit more believable

Spoiler alert: Any would likely be microscopic
Jul 31, 2018 — 10:01 am EST
an image of Mars' south pole

Scientists found what they think is a lake hidden under ice (white) near Mars’ south pole, seen in this image from the European Space Agency’s Mars Express spacecraft.

ESA, DLR, FU BERLIN (CC BY-SA 3.0 IGO)

The search for life on Mars just got a lot more interesting. The odds are slim that Mars hosts life today. Still, a newly spotted lake near the Red Planet’s south pole ups the chances that scientists could find microbes living on Mars today.

For decades, when scientists looked at the dry and dusty planet, they focused on sites that might have supported life when Mars was warmer and wetter. But on July 25, researchers announced finding signs of a large lake of liquid water. It appears to be hiding beneath thick layers of ice near the Red Planet’s south pole. And it could provide a reservoir for salt-adapted organisms.

The increased possibility of life also changes the strategy of astrobiologists. They want to protect any existing extraterrestrials from being wiped out or overrun by species hitchhiking in on Earthly spacecraft.

Mars landers and rovers are carefully cleaned to avoid any possible contamination. And that was true even before there appeared to be “anything you’d even call a pond,” says Lisa Pratt. She’s an astrobiologist and NASA’s official planetary protection officer. “Now we have a report of a possible subglacial lake!” That, she notes, is “a major change in the kind of environment we’re trying to protect.”

So how does finding the lake change the quest for life on Mars?

First: Could anything really live in this lake?

It would be a tough territory for most Earthly microbes. Life on Earth fills every niche it can find, from cave crystals and arid deserts to sediments on the deep-ocean floor.  But the low temperature cutoff for most life on Earth is around –40° Celsius (-40° Fahrenheit). The Martian ice sheet is about –68 °C (–76 °F). “It’s very cold — colder than any environment on Earth where biologists believe life [can live and reproduce],” Pratt says.

The lake does seem to contain plenty of water. But for the water to be liquid at such cold temperatures, it also must be extremely salty. “On Earth, these kinds of briny mixtures present significant challenges to living organisms,” says Jim Bell. He’s a planetary scientist at Arizona State University in Tempe and president of the Planetary Society.

Some bacteria on Earth seem to thrive even in extreme conditions. But even the so-called “extremophiles” (Ex-TREE-moh-fyles) “that can live in highly salty water might not be able to survive” in the cold, Martian lakes, he says.

But could Martians live there?

“Absolutely,” Pratt says.

If life arose on Mars at some point in its more life-friendly past, some of those organisms might have adapted to the Red Planet’s changing climate. These might have ended up finding the cold, salty water quite comfortable, she says. “This to me looks like an ideal refugia — a place where you could just hang out, maybe be dormant and wait for surface conditions to get better.”

What’s different about this lake versus other watery places where we hope to find life, like Saturn’s moon Enceladus?

For planetary explorers, Mars has one big advantage over the icy moons of Saturn and Jupiter: We’ve landed on it before. Getting to Mars would be a relatively quick journey. A spacecraft could reach there in four to 11 months. And the planet’s atmosphere makes landing much simpler than on the tiny, airless moons.

The big question for planetary protection is whether Mars’ lake has any contact with the planet’s surface. On Saturn’s moon Enceladus and possibly on Jupiter’s moon Europa, liquid water from a subsurface ocean sprays into space from cracks in the ice. Those plumes would make sampling the oceans relatively simple: A spacecraft could just catch some spray during a flyby. But the fact that water can get out also means that invading microbes can get in.

Even though no Mars spacecraft has landed near the suspected lake, global dust storms — like one currently raging on Mars — could carry in contamination from anywhere on the planet.

“So if [the lake is] real, let’s hope there’s no passageway into it,” Pratt says.

If there’s no way in or out, how can we see if anything lives there?

That is a problem. But it’s also not impossible to overcome.

To check the lake for signs of life, “you gotta drill,” explains Isaac Smith. He’s a planetary scientist in Lakewood, Colo., working for the Planetary Science Institute. Scientists have already probed similar under-ice lakes on Earth, such as Lake Whillans in Antarctica. In 2014, a U.S. team drilled through some 1.6 kilometers (1 mile) of ice. Each thimbleful of water they brought up contained roughly 130,000 living cells. In all, this water hosted 3,931 microbial species or groups of species.

Drilling on Mars would be even more technically challenging. It also could face opposition from the scientific community. “Like the subglacial lakes in Antarctica, [the Mars lake] would be considered an extraordinarily rare and special place,” Pratt says. “I expect there would be lots of resistance to drilling into it.”

But if we’re lucky, there could be a sign from above. Scientists have detected signs of seasonal variations in the amount of methane in the Martian atmosphere. This has suggested these variations might point to microbial life under the surface. The European Space Agency’s ExoMars Trace Gas Orbiter, which began taking data in April, is looking for more such methane.

“ExoMars could find a ‘smoking gun,’ so to say,” says Roberto Orosei. This planetary scientist works at the National Institute of Astrophysics in Bologna, Italy. He also was part of the team that just discovered the Martian lake. “Association of liquid water and methane in the atmosphere,” he says, “would be very, very exciting evidence of something going on on Mars.”

Power Words

(for more about Power Words, click here)

Antarctica     A continent mostly covered in ice, which sits in the southernmost part of the world.

arid     A description of dry areas of the world, where the climate brings too little rainfall or other precipitation to support much plant growth.

astrobiology     The study of life everywhere in the universe, including on Earth and in space. A scientist who works in this field is known as an astrobiologist.

astrophysics     An area of astronomy that deals with understanding the physical nature of stars and other objects in space. People who work in this field are known as astrophysicists.

atmosphere     The envelope of gases surrounding Earth or another planet.

bacteria     (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals).

climate     The weather conditions that typically exist in one area, in general, or over a long period.

crystal     (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The mineral crystals that make up rock are usually too small to be seen with the unaided eye.

dormant     Inactive to the point where normal body functions are suspended or slowed down.

dust storm     A moving, blowing cloud of dust carried by the wind.

ecosystem     A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra. The term can also be applied to elements that make up some an artificial environment, such as a company, classroom or the internet.

Enceladus     The sixth largest of Saturn’s more than 50 moons. Enceladus is bright white and covered with a thick shell of ice. Deep beneath that ice sits what appears to be a global ocean of salty liquid water. Enceladus is a round sphere, 500 kilometers (310 miles) across. It is a little less than one-third the width of Earth's moon.

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).

Europa     One of the moons of Jupiter and the sixth-closest satellite to the planet. Europa, 1,951 miles across, has a network of dark lines on a bright, icy surface.

extraterrestrial     (ET) Anything of or from regions beyond Earth.

extremophile     A microorganism that lives in conditions of extreme temperature, acidity, alkalinity or concentrations of chemicals.

host      (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.

ice sheet     A broad blanket of ice, often kilometers deep. Ice sheets currently cover most of Antarctica. An ice sheet also blankets most of Greenland. During the last glaciation, ice sheets also covered much of North America and Europe.

Jupiter     (in astronomy) The solar system’s largest planet, it has the shortest day length (10 hours). A gas giant, its low density indicates that this planet is composed of light elements, such as hydrogen and helium. This planet also releases more heat than it receives from the sun as gravity compresses its mass (and slowly shrinks the planet).

lander     A special, small vehicle designed to ferry humans or scientific equipment between a spacecraft and the celestial body they will explore.

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.

moon     The natural satellite of any planet.

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.

niche     A small or narrow pocket that sets something apart, or perhaps offers a region of protection.

online     (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.

orbiter     A spacecraft designed to go into orbit, especially one not intended to land.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

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.

planetary science     The science of planets other than Earth.

plume     (in biology) A single large feather. (in environmental sciences) The movement of some gas or liquid, under the direction of gravity, winds or currents. It may be in air, soil or water. It gets its name from the fact that it tends to be long and relatively thin, shaped like a large feather. (in geology) Fluids (air, water or magma typically) that move, largely intact, in a feather-like shape over long distances.

Red Planet     A nickname for Mars.

replicate     (in biology) To copy something. When viruses make new copies of themselves — essentially reproducing — this process is called replication. (in experimentation) To copy an earlier test or experiment — often an earlier test performed by someone else — and get the same general result. Replication depends upon repeating every step of a test, one by one. If a repeated experiment generates the same result as in earlier trials, scientists view this as verifying that the initial result is reliable. If results differ, the initial findings may fall into doubt. Generally, a scientific finding is not fully accepted as being real or true without replication.

resistance     (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.

Saturn     The sixth planet out from the sun in our solar system. One of the four gas giants, this planet takes 10.7 hours to rotate (completing a day) and 29 Earth years to complete one orbit of the sun. It has at least 53 known moons and 9 more candidates awaiting confirmation. But what most distinguishes this planet is the broad and flat plane of seven rings that orbit it.

sediment     Material (such as stones and sand) deposited by water, wind or glaciers.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

standards     (in research) The values or materials used as benchmarks against which other things can be compared. For instance, clocks attempt to match the official standard benchmark of time — the second, as calculated by the official atomic clock. Similarly, scientists look to identify a chemical by matching its properties against a known standard for a particular chemical. (in regulations) A limit above which something may not be used, sold or considered safe.

terrestrial     Having to do with planet Earth, especially its land. Terra is Latin for Earth.

Citation

Journal: R. Orosei et al. Radar evidence of subglacial liquid water on MarsScience. Published online July 25, 2018. doi: 10.1126/science.aar7268.