Discover The Strange-Looking Animal That Could Live On Mars

Mars is the 4^th plant from the sun and the second-smallest planet after Mercury in our Solar System. Also known as the Red Planet, Mars features a thin atmosphere and ice caps near its poles. For decades, scientists have debated whether life could have once existed on the planet. While no evidence has been found to suggest the presence of life on Mars, it begs the question; what animals could live on Mars? 

Of all the animals on Earth, the tardigrade may be the only animal that could survive on Mars. These amazing microscopic animals are practically immortal and have evolved some incredible survival tactics. Keep reading to learn more about this strange-looking animal that could live on Mars.

5 Tardigrade Facts

• Tardigrades measure as little as 0.5 millimeters long, making them just barely perceptible with the naked eye. 
• To date, scientists have identified approximately 1,300 different tardigrade species. 
• For a short time, tardigrades can survive temperatures below -272.15 degrees Celsius and up to 150 degrees Celsius. 
• Tardigrades can withstand pressures six times greater than the pressure at the bottom of the ocean. 
• If a tardigrade loses 99% of its water content, it can pause most of its vital functions to survive for several years in a near-suspended state. 

Name

The tardigrade goes by several other names, including the water bear or moss piglet. German zoologist Johann August Ephraim Goeze first described the tardigrade in 1773. Goeze named the tardigrade Kleiner Wasserbar, meaning “little water bear.” A few years later, the Italian biologist Lazzaro Spallanzani also described the tiny animal as Tardigrada, meaning “slow steppers.” This is the origin of its current name.

Tardigrade Appearance

On average, adult tardigrades measure around 1 millimeter long. However, they can range anywhere from 0.5 millimeters to 1.5 millimeters long, with females typically measuring larger than males. Their bodies are roughly cylindrical and consist of a cephalic (head) segment and four trunk or body segments. Each trunk segment features two legs, one on each side, for a total of eight legs. The legs don’t contain joints and end in feet that sport anywhere from two to eight claws. A tardigrade’s first three pairs of legs point downward and are used for movement. Meanwhile, the rear pair point backward and are used to root the tardigrade to the ground. 

The body of a tardigrade is covered by a waxy, protective layer known as a cuticle. This cuticle is made of protein and chitin and is molted periodically. The cuticle appears somewhat fluffy or squishy, lending the tardigrade its unique appearance. While most tardigrades appear either translucent or white, they can vary in color from yellow to green to orange.

Evolution And Taxonomy

Most evidence suggests that tardigrades descended from a larger ancestor. However, the source of that ancestor remains up for debate. Most likely, tardigrades evolved from a species of lobopod, a type of stubby-legged panarthropod. 

Scientists have identified two groups that are closely related to tardigrades. Arthropods and velvet worms make up the first group, while nematodes make up the second. In terms of appearance, tardigrades resemble velvet worms and other arthropods. However, when you examine their molecular structure, tardigrades share more in common with nematodes. Despite some evidence of molecular similarities with nematodes, most experts place tardigrades in their own phylum (Tardigrada) next to the clade Antennopoda, which includes the phylum Arthropoda (arthropods) and Onychophora (velvet worms).

The oldest tardigrade remains date back to the Late Cretaceous around 90 million years ago. That said, tardigrades may have evolved even earlier. Most tardigrade fossils are found encased in amber, which preserves the body of the tardigrade. 

Habitat

You can find tardigrades in almost every habitat on earth. They range from mountains to coastal dunes and from the barren landscapes of Antarctica to the lush rainforests of the Amazon. Although some tardigrades are terrestrial, all tardigrades require water around their bodies to stay hydrated and permit gas exchange. As a result, all tardigrades are classified as aquatic organisms. You can typically find them in freshwater habitats such as rivers, lakes, and ponds. On land, they often live on moss, lichen, soil, or leaves covered in a layer of water. 

Diet

The diet of most tardigrades consists of plants (herbivores) or bacteria (bacterivores). Some common foods that plant-eating tardigrades eat include algae, moss, and flowering plants. Meanwhile, a select group of tardigrades lives on a carnivorous diet. These tardigrades mostly eat other, smaller tardigrades, as well as rotifers, a type of microscopic animal.  

Tardigrades are equipped with a tubular mouth covered in stylets. They use these hard, sharp mouthparts to pierce the cells of a plant, bacteria, or invertebrate, which the tardigrade then sucks inside its mouth. Tardigrades lose their stylets when they molt and grow new stylets from a pair of glands on each side of the mouth. Food travels down the mouth through the esophagus and into the intestine, where it gets digested.  

Reproduction

Most tardigrades reproduce via mating between a male and a female. However, some species are parthenogenic, meaning they reproduce asexually. In sexual reproduction, males fertilize the female’s eggs externally. Mating occurs during the molting period. While most females lay their eggs inside their shed cuticle, some attach their eggs to the ground. The males then fertilize the eggs by covering them in sperm. 

After around 14 days, the tardigrade eggs hatch. Juvenile tardigrades possess the same number of cells as adult tardigrades. Instead of generating new cells to grow, tardigrades simply increase the size of their cells. During its lifetime, the average tardigrade may molt up to 12 times. 

Survivability

Tardigrades are one of the toughest animals on earth. They can withstand conditions that would kill most other creatures, as evidenced by the fact that they have survived all five recognized mass extinction events in world history. 

Tardigrades can withstand extremely cold and hot temperatures. On the low end of the spectrum, they can survive temperatures up to -272.15 degrees Celsius. Similarly, they can also withstand temperatures up to 150 degrees Celsius for several minutes. They can also withstand extremely low and high pressures. Tardigrades can survive at altitudes over 19,600 feet above sea level and at depths of over 15,000 feet below the surface. They can absorb powerful impacts that would crush other creatures. They can also absorb radiation levels strong enough to kill a human. These amazing creatures can even survive in the vacuum of outer space for a short time! 

That said, tardigrades cannot survive these harsh environments indefinitely. Rather, they are able to endure these conditions for a specific period of time. Tardigrades manage to survive these conditions thanks to their unique metabolic properties. They can suspend their metabolism to less than 0.01% of normal to survive in environments that cannot normally sustain life. In this state, they dry out and lose up to 90% of their water content. Tardigrades can survive up to 30 years without food or water in this suspended state. Upon rehydrating, they can return to normal functions, including eating and reproducing. That said, most tardigrades can only last for a few years in a dehydrated state. 

Tardigrades could technically survive on Mars due to the presence of water (ice) on the planet. However, they could not survive indefinitely due to one reason: a lack of food. Without food, any tardigrades introduced to the planet would slowly starve to death.