25 of your most frequently asked questions about tardigrades answered!

Tardigrades are by far the undisputed champions of nature's contest for survival, but just how tough are they? We've got the answer to that and many more questions about tardigrades.
John Loeffler

The tardigrade, more commonly known as the water bear, has been in the news lately following the recent revelation that thousands of them were onboard SpaceIL's Baresheet spacecraft when it crashed on the surface of the moon earlier this year--and that the disks they were held in might have survived the impact intact. For any other life form on Earth, their ultimate fate would be clear: an inevitable death from exposure to the vacuum of space. But tardigrades aren't just any life form.

The fact that the survival of the tardigrades on the surface of the moon is even remotely possible should tell you that these creatures are special, but you don't need to go to the surface of the moon to prove that; what they are capable of right here on Earth is more than enough to earn these incredible creatures a unique place in our planet's Tree of Life.

If you've only just discovered the tardigrade and are wondering how something that looks like a plump sausage on legs could be as tough as people say it is, you're in luck. We set out to answer the most common questions people have about the tardigrade to help give a fuller picture of not just what makes them so unique, but also how they are as much a product of the evolutionary process as the rest of us.

What is a tardigrade, exactly?

25 of your most frequently asked questions about tardigrades answered!
Source: ESA/Ralph O. Shill, via NASA

A tardigrade is a microscopic, water-dwelling organism belonging to the phylum Tardigrada, and the name tardigrade is used to generally refer to any species under that phylum. While we do something similar with other phyla, like arthropods, when we talk about tardigrades we are usually being much more specific.

Practically speaking, being a tardigrade has much more of an influence on a member species than the levels of classification below the phylum. The morphological and genetic diversity within Tardigrada is much more narrow than is usually the case with other, typically larger phyla.

Are tardigrades a kind of bacteria?

Tardigrades are some of the oldest organisms we know of and are a product of one of the earliest differentiations in the evolution of life on this planet. They evolved from some of the earliest eukaryotic cells--meaning that their genetic material is housed in a central nucleus--which already puts them one important step removed from bacteria, which are not eukaryotic. What's more, tardigrades are multicellular, which further distinguishes them from bacteria that never evolved beyond a single cell.

Back in 2015, a study argued that the genome of some tardigrade species contained a significant amount of bacterial DNA, leading some to call them a form of hybrid organism. That study has since been discounted after another study found that this bacterial DNA in the tardigrade genome was actually a contaminant and not part of the genome itself. The original story made a lot of headlines at the time while the subsequent correction received much less attention in the press. This might leave some with the incorrect belief that tardigrades somehow overlap with bacteria when no such connection exists.

Where do tardigrades actually belong in the Tree of Life?

Side-stepping the usually-heated debates around taxonomic classification, it is clear from the cells of tardigrades that their phylum falls under the Eukaryotic kingdom of Animalia. Beyond that, their closest relatives are possibly the anthropods but there isn't a clear connection between them, or any other phylum in Animalia for that matter, so part of the mystery of tardigrades is that no one really knows for sure where they belong.

What do tardigrades eat?

Predominantly, tardigrades eat fluids; which sounds weird, but it's a pretty important weirdness. The diet of a typical tardigrade consists of sucking the nutrient-rich goop out of plant and animal cells. No matter the type of cell, the tardigrade's claws and distinctive telescopic mouth are designed to tear open and puncture cell walls and membranes, allowing it can stick its mouth into all the gooey innards and slurp up whatever it can get to.

Fortunately, they also like to feast on bacteria, so if any of this sounds somewhat gruesome, you can just imagine that they're doing their part to prevent the kinds of grim, world-ending plagues like Yersinia pestis that have stalked humanity throughout our history.

Some species of tardigrade are also straight-up cannibals who kill and devour other tardigrades, even those of the same species as themselves.

How do tardigrades reproduce?

Tardigrades can reproduce both asexually and sexually, depending on the species or the environment.

For those species that reproduce sexually, the female 'lays' anywhere from one to thirty eggs at a time and which are implanted into an outer layer of molted skin. A male will then come along a wrap itself around the female. They will then go through a process of mutual stimulation which ends with the male ejaculating its semen onto the female's freshly molted skin where it will fertilize the eggs contained within.

Scientists recently conducted a study where they watched nearly three dozen pairs of mating tardigrades and were able to record it for the first time ever.

The results of this observation are significant since they show that for some species of tardigrade fertilization takes place outside of the female's body, though what happens next or how the sperm is directed toward the actual eggs is not known at this time.

What is the physiology of the tardigrade like?

25 of your most frequently asked questions about tardigrades answered!
Source: Frank Fox/Wikimedia Commons

The appearance of the tardigrade is similar to an eight-legged bear with a mouth that can project out like a telescopic tongue. Its body is made up of four segmented sections that make up its trunk which sits on four pairs of clawed legs.

Each set of claws is sharp enough to do some pretty serious damage relative to their size and their gait while swimming or crawling around is reminiscent of actual bears. The tardigrade's hind legs meanwhile are pointed up towards the front of its body and in the opposite direction from the rest of its legs, creating a kind of grasping, opposable leg arrangement that allows it to better cling to whatever it is trying to eat, kill, or mate with.

The skin of a tardigrade is generally thin enough to be functionally transparent under a microscope, but they can also look something like gummy bears in natural light.

With the right set-up, students and amateur biologists are able to study the physiology of the tardigrade in remarkable detail. Since they are large enough to be very clearly seen with even a modest microscope and it is easy to see the internal organs and biological functions taking place beneath their relatively thin skin, tardigrades are usually one of the first things students and aspiring biologists study.

Are tardigrades dangerous?

No, at least not to humans. Other micro-organisms in their environment should be on notice though; those claws aren't for show. While most tardigrades are herbivorous, not all of them are, and they will eat you if you are smaller than they are and you are within reach of their claws.

Despite their reputation, tardigrades aren't entirely indestructible. They cannot survive the trip through the human digestive tract since our stomach acid disintegrates the flesh of the tardigrade without much trouble, so eating one wouldn't do any harm. So far, no one has reported a case where a disease or infection was introduced into the human body via tardigrade, and they aren't parasitic. It's possible that they might try to suck out the contents of one of the individual cells that make up our body if they ever came into contact with it, but we've got trillions more. Getting eaten alive by tardigrades just isn't something that's going to ever happen.

Moreover, we know this is the case since we've all been eating tardigrades for as long as we've been on this planet. Wherever you find water and vegetation, you're going to find tardigrades. They are likely all over the lettuce, tomatoes, and other vegetable matter found in an average salad, but there haven't been any reported cases of food-borne tardigrade poisoning.

Where do tardigrades live?

Tardigrades are most commonly found wherever there is a body of freshwater, no matter how deep, but they can also live on land and even in the ocean. They've been found at the tops of mountains and at the very bottom of the Mariana Trench. You can find some species of tardigrade in just about any corner of the world you can imagine.

How big are tardigrades?

When they're in their active state--more on this later--tardigrades are about half a millimeter in length. When they are inactive, they curl up to about half their normal size. They can also lengthen their bodies in certain circumstances, stretching out to more than a millimeter in length.

How many kinds of tardigrades are there?

Depending on which form of classification you go with, there are at least 900 different species of tardigrade but others say there are more than 1,000.

Who discovered the tardigrade?

25 of your most frequently asked questions about tardigrades answered!
Source: Internet Archive Book Images/Flickr

The tardigrade was first described in scientific literature by Johann August Ephraim Goeze, a pastor and natural scientist from Quedlinburg in modern-day Germany, in the year 1773. He was the first to note their distinctive bear-like appearance when he said: "Strange is this little animal, because of its exceptional and strange morphology and because it closely resembles a bear in miniature."

Where did the name "tardigrade" come from?

The Italian biologist Lazzaro Spallanzani gave the creatures the name Tardigrada in 1776, which means 'slow stepper.' Spallanzani only meant to describe a single species, but soon the name Tardigrada was extended to refer to the entire phylum rather than any individual species.

Why are they called water bears?

The origin of the name water bear comes from Goeze's 1773 paper since that is what he called the creatures he was describing. By 1773 however, the binomial, Latinized naming system that we use today had already started being widely adopted, and since 'water bear' isn't Latin, it wasn't suitable for the official scientific name for the species.

The name 'water bear' stuck around though because it is a very evocative description of the creature and, honestly, it sounds cute, making it a natural informal, and affectionate name for the animal. They are also sometimes called 'moss piglets,' which is equally adorable.

What is a tun?

A tun is nothing short of a biological time capsule and the key to a tardigrade's extraordinary survivability.

In extremely inhospitable conditions that would typically kill a normal lifeform, tardigrades essentially check out for a while, turning themselves into something called a tun. A tun is the hardened form of the tardigrade after it curls up into itself and replaces the water content of its cells with different substances depending on the specific environmental challenge. This has the effect of essentially turning a tardigrade into a very durable piece of glass.

25 of your most frequently asked questions about tardigrades answered!
Source: T.C. Boothby/Molecular Cell

If there's no water in its environment, a special sugar called trehalose is produced that it uses to replace the missing water volume, encasing the various internal organelles and membranes of its cells, and providing reinforcement to its internal structure while it is in a form of stasis. This stasis, which walks right up to the line of biological death, is a phenomenon known as cryptobiosis. This process isn't unique to tardigrades but they have truly mastered the process to all but transform themselves into a mineral, secure in the knowledge that their cells are better protected from environmental damage than any other eukaryotic cell on the entire planet.

Are tardigrades aliens?

There are a couple of reasons why some people believe that tardigrades might be alien life forms. Their incredible ruggedness despite being so small and seemingly fragile--you can see right through the soft, watery cells of the tardigrade under a microscope, so they aren't exactly thick-skinned--isn't something that can be easily traced through the fossil record. Tardigrades have a number of survival mechanisms that, when taken together, make them look like something otherworldly.

There are no proto-tardigrade species that clearly show how tardigrades built up these adaptations over hundreds of millions of years. That sort of thing just isn't the sort of thing that gets preserved in fossils. Like feathers on a T-Rex, things like cryptobiosis just can't be easily identified by looking at fossilized tardigrades.

So, to a casual observer, a tardigrade can look like it dropped out of evolutionary thin air as some kind of ready-made, super-resilient lifeform. Together with the fact that tardigrades have been observed surviving the most inhospitable environments planet Earth can throw at them, the theory that they hitched a ride on an alien asteroid and subsequently set up shop here on Earth can be made to fit a certain set of very true facts about tardigrades.

That said, very few professional biologists believe that tardigrades originated somewhere other than Earth. Their significance to the field of astrobiology has more to do with the fact that studying how tardigrades have adapted to extreme conditions gives us valuable insight into how alien life may be able to develop on worlds with a radically different environment than our own.

Besides, for all their distinctive biological adaptations, they are still much more alike to animal life here on Earth than any alien life form is likely to be. They may have branched off from the rest of animal life in the very earliest days of multicellular evolution, but this early branching and incredible longevity are more than enough to explain their biology.

Tardigrades have been around for more than 500 million years and have survived all five mass extinctions this planet has gone through. Extinctions generally erase some evolutionary paths in favor of others, causing novel adaptations to disappear entirely while new evolutionary paths sprout from the remains of the old. But what if you were able to avoid this erasure by being one of the few species to survive? Those novel adaptations would be preserved and passed on, letting descendants build off what came before rather than starting over with something else.   

Such a long, relatively-intact transmission of genetic material within the phylum would allow all kinds of adaptations to accumulate over time in response to environments that might not even exist anymore. You wouldn't need a theory involving alien life forms hitching a ride on an asteroid to explain how tardigrades got here, you just need to have them come up in the very early days of multi-cellular life on this planet and then put them through every hellish comet impact, supervolcano eruption, major ice age, and miscellaneous geological trauma that life on this planet has had to endure over the eons while staying more or less in the same state of multicellular development.

Tardigrades aren't aliens, they're more like grizzled war veterans who know all sorts of things new recruits don't.

Can tardigrades really survive in space?

Yes, for a time. In 2007, researchers in Europe sent tardigrades into space to test the limits of what they were able to endure. For 10 days, dehydrated tardigrades were exposed to the vacuum of low-Earth orbit. Upon returning them to Earth, the researchers rehydrated them, and a number of them were successfully revived and went on to produce viable offspring. No other lifeform has been known to exhibit anything similar to this level of adaptability, so it's not hard to see why some began to speculate that they might have originated off-world.

Is it true that tardigrades can withstand high levels of radiation exposure?

The other important result of the 2007 vacuum exposure experiment involving the dehydrated tardigrades was that one group of exposed tardigrades was shielded from the sun's radiation, which is at its full intensity in space. Another group of dehydrated tardigrades took this blast of radiation full-on, facing a dose of X-ray radiation 1,000 times what would be considered lethal for human beings. It's the kind of radiation that will slowly disintegrate the Tesla Roadster that Elon Musk sent into orbit around the sun during the first Falcon Heavy test launch. It is no joke.

Unsurprisingly, most of the unshielded specimens were killed by the radiation, but incredibly some were able to survive. A few of these dehydrated tardigrades were rehydrated and reanimated back on Earth, with some even able to produce viable offspring despite their DNA getting nuked by some of the strongest radiation the sun could produce.

Can tardigrades really survive without food or water for years?

25 of your most frequently asked questions about tardigrades answered!
Source: Peter von Bagh/Flickr

Not just years, but decades. In fact, tardigrades were reportedly reanimated from a dehydrated moss sample in a museum estimated to be at least 100 years old. When tardigrades go through cryptobiosis, they are not playing around.

Once a tardigrade loses about 99% of its water volume, the dehydration triggers the cryptobiosis process that turns it into a tun. Once this process is complete, their metabolic rate is reduced by as much as 99.99%. They are essentially dead in all but name and can continue in this state as long as it doesn't fully consume the energy reserves they had stored up at the moment of their desiccation.

Then, decades later, add a few drops of water to a tun, and the tardigrade will begin to rehydrate itself until the cryptobiosis has been completely reversed. It will proceed as normal and look for food to replenish the energy it lost during its cryptobiosis.

Can tardigrades really survive without oxygen?

Tardigrades need oxygen like every other animal on Earth, but they can only 'breathe' oxygen from the water around them. Take it out of its aquatic environment and it can no longer breathe or do much of anything else except dry itself out. Fortunately for the tardigrade, once cryptobiosis is triggered and it turns into a tun, the need for oxygen becomes nearly as non-existent as its need for food and water.

But that's kind of cheating since we're mixing the need for oxygen and the need for water.

What if a tardigrade is in water, but the water has lower or nearly non-existent oxygen content? This is an increasingly common phenomenon thanks to climate change, but of course, tardigrades have a way to handle that too.

If its watery environment is lacking breathable oxygen, the tardigrade can extend itself out to more than twice its length, stretching out all those cute little folds it's got to maximize the amount of surface area available for gas transfers to take place.

It doesn't really require any more oxygen than before, but it'd be similar to using four full-sized lungs, or even eight, to breathe in a low-oxygen environment for us. On top of that, the tardigrade reduces its metabolic rate significantly--though not as drastically as it does during cryptobiosis--which allows it to use its available oxygen much more sparingly until it can find more suitable waters for itself.

How do tardigrades survive extreme heat?

25 of your most frequently asked questions about tardigrades answered!
Source: Indrik Myneur/FreeStockPhotos

Tardigrades have been shown to survive temperatures as high as 304 degrees Fahrenheit, or 151 degrees Celsius, more than enough heat to evaporate away all of the water content inside their cells. As we've seen though, a tardigrade knows how to deal with dehydration, so the tardigrade has that under control.

The principal reason why excess heat is so dangerous for all but the most extremophile organisms is that heat can damage and warp the structure of the proteins that make up all of the cells in our body. Organisms are typically adapted to maintain a very narrow range of core temperature that allows their proteins to work correctly. If these proteins are warped too much, the basic life-sustaining functions that rely on these proteins maintaining a specific shape quickly stop working resulting in cell death.

This is the reason why we run a fever if we have a major infection. By increasing our body temperature, our immune system is trying to warp the proteins in the bacteria or virus past the point where the infecting organisms start dying off. The problem is our cells are affected by the increase in temperature as well, so a fever is effectively a game of chicken between the infection and our immune system to see who loses a critical mass of cells to protein warping first.

For humans, an increase of just six or seven degrees Fahrenheit is enough to kill us in very short order. If a tardigrade is used to temperatures in the typical range for animal life, how can it survive when it's suddenly 200 degrees hotter than it was designed to live in?

It does this by mass-producing a special protein that helps other proteins resist the kind of heat-induced warping that can kill the cell. As the tardigrade turns into a tun, the trehalose and this special protein create a tun whose proteins are as protected from the damaging effects of the heat as you can get.

This is more triage than a permanent solution, however. If the extreme heat goes on for too long, then the proteins making up the cell will eventually be damaged, anti-warping protein or not. The anti-warping protein is also a protein, so it too can be warped out of the specific form it needs to operate.

The tun can be burned away if it is exposed to an open flame or something like a lava flow, and the hotter it gets, the harder it becomes for the tun to hold out.

If it is able to hold on long enough for the heat danger to pass--such as when a passing wildfire burns through the tardigrade's habitat only to die out once the available fuel is used up--then the tun will stay in its cryptobiosis until it can be rehydrated.

How are tardigrades able to survive the extreme cold?

25 of your most frequently asked questions about tardigrades answered!
Source: US National Parks Service

Through more or less the same process it uses to survive extreme heat, tardigrades have been recovered and reanimated after enduring temperatures as low as -328 degrees Fahrenheit, or -200 Celsius.

Rather than having to deal with protein warping, when dealing with the cold, the biggest danger to the tardigrade is the same as it is for every other animal or plant: water, or more specifically, ice.

Water expands in volume when it freezes into ice, so in response to extreme cold, the tardigrade expels as much water from its body as possible through--you guessed it--cryptobiosis.

After expelling more than 99% of its water volume, it has to deal with the remaining water, since the formation of ice crystals within a cell can cause irreversible damage and is often fatal. So, to prevent crystals from forming around or in the organelles of its cells, the tardigrade's cells start pumping out glycerol, which acts as an anti-freezing agent, alongside the trehalose that will support the bodily integrity of the tardigrade while it is a tun.

Tuns have been recovered and reanimated after being frozen in solid ice for decades, which is of special interest to medical researchers who are exploring how to get the same effect as the tardigrade's cold-induced cryptobiosis. If they could find a way to recreate in other cells what the tardigrade does internally, it could revolutionize the storage and preservation of essential medical tissue, such as sperm and egg cells, blood used for transfusions, and possibly even entire organs that can be used for transplantation.

None of these can be preserved long-term through freezing since human cells don't have a way to expel the water contain inside them. anti-freezing agents can be used but currently aren't a long-term solution. They cannot completely prevent the formation of ice crystals in a cell that is made up of 90% water. With that much water turning to ice inside the cell's organelles and membranes, they are going to have more holes in it than a heavily trafficked road after a wet and brutally cold winter.

If we could find a way to reproduce the tardigrade's anti-freezing process in human cells, though, calling it a revolutionary development for medicine would be a major understatement.

Are tardigrades considered extremophiles?

25 of your most frequently asked questions about tardigrades answered!
Source: Frank Fox/Wikimedia Commons

Many people consider tardigrades to be extremophiles, but that is debatable. Just because tardigrades have adapted to survive some pretty brutal conditions, that doesn't mean that they like those conditions and seek them out the way true extremophiles do. Tardigrades look for mossy, temperate water to live in and all of their adaptations are designed to protect them in case their habitat changes rapidly, like when a lake dries out or freezes over during the winter.

There is also a limit to tardigrade toughness. Expose it to direct solar radiation and it might survive for a surprisingly long time, but with each passing second, the chances of surviving the ordeal grow increasingly small. 

Cryptobiosis might be a half-step away from biological death, but it is not biological death. The tun's metabolism might be a hundredth of a percent of what it normally is, but it will still burn through its energy stores eventually. At some point, there will be nothing left for the tardigrade to use to keep its metabolism going at any level and its cells will begin to die.

Trap a tardigrade in a glacier for a couple of hundred thousand years and what you'll get is a fossil. Roast it in an active volcano and you'll produce a speck of char that no amount of water can reanimate. As tough as a tun may be, deny it water, food, or oxygen for long enough, and eventually the tun simply becomes a corpse.

How do tardigrades move around?

There are really two questions here. How do tardigrades move through their environment, and how do tardigrades move from environment to environment? Locally, tardigrades swim around using their legs as paddles just like larger animals do. How they move from environment to environment, however, is much more interesting.

So when a tardigrade's environment dries out or becomes otherwise inhospitable, cryptobiosis kicks in and the tardigrade becomes a tun. Now it could try to tough it out and wait for the environment to return to a more hospitable state, which would be pretty impressive on its own, but instead, many tuns do something different: they migrate elsewhere.

I know, they're a tun, they're supposed to be all but dead so how can they up and migrate somewhere else? Fortunately, while the tardigrade might be in a state of cryptobiosis, the world around them doesn't slow down. The hardened mud they might be trapped in after a lake dries out will slowly but inevitably get weathered away by the wind or passing animals. Whatever the cause, at some point, the microscopic organism will be displaced and weighing almost nothing, can be carried off by some external process like the wind or by piggybacking off some other animal.

Whatever the means, the result is that the tun will move from place to place. If the environment it lands in is inhospitable, the tun remains a tun and will keep getting moved from one place to the next.

Eventually, though, odds are good that the tun will land in water or some other wet environment and it will begin to rehydrate. Several hours later, the cryptobiosis will be reversed and the tardigrade will go about its business. A tardigrade can even reproduce asexually if it is the only tardigrade in its local area, from which an entirely new colony of tardigrades can be grown.

If this sounds somewhat familiar, it's probably because this process is similar to how many plant species spread seeds and pollen on the wind or on the backs of insects to spread out over an area or to migrate to a less populated area so as to maximize the amount of sunlight and nutrients that they can claim for themselves.

The mobile tun also sounds a lot like a fungal spore, which enables fungi to asexually reproduce to create new colonies in a new environment in a very short amount of time.

If we think back to that reportedly century-old piece of dried-up moss at the museum that carried all those 100-year-old tuns along with it, we can't help but be amazed at the ingenuity of this process.

When the museum moss was first collected, cataloged, and locked away over a century ago, the tardigrades that called that patch of spongey surface home suddenly found themselves in an inhospitable environment. So, they turned themselves into tuns and waited over a century for someone or something to bring them to an environment that could live in. This is exactly what the researchers who reanimated the tuns did by putting them in water to see if they'd come back to life.

Granted, the rehydration for those tuns was entirely intentional on our part so it may seem silly to think that those tardigrades were relying on us to reanimate them in the first place, but that's pretty much the case. No one asked whether bees ever agreed to spread pollen around in exchange for sucking up the nectar of a flower in bloom, the system simply evolved to produce this arrangement.

For all our sense of distance from the animal world, we are very much a part of it, and tardigrades evolved a mechanism to harness the labor of other animals, including humans, to help ensure their survival.

How can you collect and study tardigrades?

If you'd like to study tardigrades for yourself, you can go hunting in your backyard or along lakes, ponds, or other similarly wet sites. Find some moss, gather up some samples, and bring them back to whatever you're using as a workspace. The main trouble with studying the tardigrades you collected is that they are less than a millimeter in length and looking at a large clump of moss isn't a very effective way to look at tardigrades. Instead, you'll need to draw them out of the moss and isolate them for easier study.

Microscopy-UK recommends following these steps if you want to draw out any tardigrades that might be hiding in the moss samples you've collected:

* Set the moss samples--dry or wet samples work equally well--in a small shallow petri dish. * Pour some collected rainwater over the moss samples in the dish until they are sufficiently wet. There will be about 1 cm of water in the dish at this point. * Let the moss samples sit in the water for several hours or even overnight. * Pour out the excess water from the dish. You won't be needing it after this, so you can pour it down the drain in your sink. * Squeeze the moss samples hard enough to wring out any remaining water into a watch glass or different petri dish. * Using a stereo microscope set to ca. 40x or an equivalently powerful setup, search through the water squeezed from the moss for any tardigrades. * 0.47 mm isn't that small as far as microorganisms go, so if there are any tardigrades in the moss water, you shouldn't have too much trouble spotting them. * Using a black background and incident instead of transmitted light can also help you spot them if you are having difficulty finding some. * There are likely to be all sorts of microbes in the moss water but don't worry.  Tardigrades have a distinctive look that's hard to mistake for anything else. * Once you've spotted a tardigrade, collect it using a glass pipette, a fine pipette is recommended, and transfer the specimen to a microscope slide. * Be careful when using slide covers! Sure, tardigrades are tiny but don't be fooled. Pressing a slide cover onto a slide with tardigrades on it can crush the poor things. * Use tiny dabs of petroleum jelly at the corners of the slide over to support it so it doesn't kill your tardigrade specimen. * The tardigrade should be easy to see and study under a compound microscope at medium or high power.

How likely is it that the tardigrades on the moon are still alive?

25 of your most frequently asked questions about tardigrades answered!
Source: SpaceIL/Twitter

So, now that you know a lot more about tardigrades, you can understand why the Beresheet Lunar Lander crash has generated some excitement as far as tardigrades go.

The Arch Mission Foundation (AMF) is a non-profit organization founded in 2015 by entrepreneur Nova Spivack with the goal of establishing "a backup of planet Earth" on the moon, creating a 'lunar library' with as much information as possible about our planet, its life forms, and human civilization 'off-site'. In the event of some civilization-disrupting catastrophe on Earth, as much human knowledge as we were able to transport to the moon will serve as a recoverable backup for humanity once civilization recovers.

If humanity, or even life itself, is entirely wiped out on our planet, then the lunar library will at least serve as a lasting memorial for life on Earth for any potential aliens who stumble upon it. As unlikely as that probably is, there's some comfort in knowing that at least until the sun grows old and becomes a red giant the size of the inner solar system a few billion years from now, we'll at least have left a trace of our existence behind for others.

The first entry in this library was loaded onto SpaceIL's privately-funded and operated spacecraft, the Beresheet Lunar Lander. Planners were hoping that it would become the first private spacecraft to land on the moon and expand the horizons for private space exploration in the process. Back on April 11, however, the Beresheet lander was attempting to make a soft touchdown in the moon's so-called Sea of Serenity when disaster struck. Just as it was coming to land, a software malfunction disrupted the lander's systems, cutting off communication with SpaceIL mission control in Israel. 

When communications were restored, the Beresheet Lunar Lander's main descent engine was shut down and the spacecraft was in a free-fall from a height of more than 10 km above the moon's surface. Rather than a soft landing, the Beresheet lander crashed into the surface of the moon at more than 2,200 mph. From that height and at that speed, Beresheet's lander wasn't so much a spacecraft as it was a bomb, releasing enough energy upon impact to completely destroy the lander and whatever was in it.

25 of your most frequently asked questions about tardigrades answered!
Before and after images taken from orbit about the Beresheet Lunar Lander crash site. Source:NASA/GSFC/Arizona State University

Right smack in the middle of that explosion was AMFs nickel-metal disk containing the collection of digitized and analog records. Only about the size of a DVD, it would seem to be a near-total certainty that AMF's disk was obliterated in the impact explosion but AMF was guardedly optimistic back in April that their archive survived the crash.

“We think it is highly unlikely that the Lunar Library was atomized in the impact,” AMF officials wrote at the time. “Without knowing the impact energy directed at the library, it’s hard to know how the stack fared. But taking the construction of the Lunar Library into account, we believe it has a high chance of being intact.”

As it turns out, AMF's storage device is no ordinary hard drive. According to Wired, "The lunar library on the Beresheet lander consisted of 25 layers of nickel, each only a few microns thick. The first four layers contain roughly 60,000 high-resolution images of book pages, which include language primers, textbooks, and keys to decoding the other 21 layers. Those layers hold nearly all of the English Wikipedia, thousands of classic books, and even the secrets to David Copperfield’s magic tricks."

Built with the expectation that the library would need to survive for billions of years, the disk itself is actually stronger than you might think. The 25 layers of nickel are held together with an epoxy agent that is designed to protect the data on the disk layers from radiation. It's these epoxy layers, in fact, that lead AMF to believe that the disk might still be intact on the surface of the moon.

"In the best-case scenario," according to Wired, "Beresheet ejected the Arch Mission Foundation’s lunar library during impact and it lies in one piece somewhere near the crash site. But Spivack says that even if the library broke into pieces, their analysis shows that these fragments would be large enough to retrieve most of the analog information in the first four layers."

The disk also contains something else: tardigrades. Dehydrated tardigrade tuns along with other biological samples were encased in the epoxy, which has some very humbling implications for the future.

Should some space-faring race of aliens discover the library long after we have passed from the history of the universe, after deciphering our languages and reaching the Wikipedia article on tardigrades contained on the disk, it's entirely possible that they could attempt to rehydrate the tuns we left behind for them. While it is highly unlikely that the tuns would survive hundreds--much less thousands or millions--of years, there is still a great deal we don't know about them, so we can't rule out the possibility of their survival. They have literally pulled that trick on us before.

And since the amber-like substance that encases them also provides a certain degree of protection from the ravages of solar radiation, these lunar tardigrades have a much better shot at surviving long-term than if they were completely exposed to the vacuum of space. Along with the epoxy-encased tuns, AMF also sprinkled thousands of tardigrade tuns on a strip of tape that was then wrapped in an insulating material and sent alongside the disk on the Beresheet lander, so there are even more opportunities for at least a few tardigrades to survive. And if we were going to gamble on which life form from Earth was most likely to survive on the moon until some alien finds them long after we're gone, a tardigrade is going to be your best bet, hands down.

So, should some life-annihilating catastrophe befall our planet in the future, the tardigrades on the moon could end up being Earth's last remaining--as well as one of our oldest--biological legacies. How wild would it be if, of all the life forms on our planet, it turned out to be the tiny, ancient, and oddly-loveable tardigrades that end up being the last remnant of life from our planet that some alien race discovers and introduce into the wider Universe? If that's not adaptability, then the word no longer has any meaning.

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