Creatures that cannot be killed by space radiation are brought to an end by humans

On February 22, 2019, hundreds of thousands of Israelis looked toward the distant space.

Their lunar probe, Beresheet, is about to land on the moon, and if successful, Israel will become the fourth country to soft-land on the moon after the United States, the Soviet Union and China. This is the world's first privately funded lunar lander, operated by Israeli nonprofit SpaceIL and Israel Aerospace Industries (IAI). Not only that, it is also the smallest and cheapest spacecraft ever to carry out a lunar mission.

At first, everything went very smoothly. However, with about ten minutes to go before the scheduled landing, a series of technical failures occurred. First, there was a problem with the star tracker on Beresheet, which prevented engineers from determining its orientation in space. Second, the only computer on this "affordable" lander inexplicably kept restarting during the mission. Finally, while restarting and landing, Beresheet crashed into the moon at a speed of more than 3,000 kilometers per hour.

Everyone had high hopes for Genesis. They even put a "Lunar Library" on the lander, which is composed of 25 layers of 40-micron-thick nickel foil, full of human civilization. The first four layers are etched with micro-images of 30 million pages of documents and photos by nanolithography technology; the last 21 layers are CD masters, storing more than 100GB of compressed files. The "Lunar Library" belongs to a non-profit organization, the Arch Mission Foundation, which has been committed to establishing multiple storage warehouses for human knowledge in and around the solar system.

Lunar library. Image credit: Arch Mission Foundation

At this time, the frustrated SpaceIL members did not know that just a few weeks before the Ark Mission Foundation delivered the "Lunar Library" to them, the founder of the foundation, Nova Spivack, suddenly decided that some DNA samples must be added to the "Lunar Library" no matter what.

Inspired by the amber formed by resin used by nature to preserve Earth creatures hundreds of millions of years ago, scientists and engineers at the Ark Mission Foundation decided to use epoxy resin to make "artificial amber." They mixed hair follicles and blood samples from Spivak and 24 other people, as well as biological samples from some holy places (such as the Bodhi tree in India) and dehydrated water bears into the resin, added it thinly between each layer of nickel foil, and sprinkled thousands of dehydrated water bears on the high-temperature insulating tape that wrapped the "Lunar Library."

As a result, these tardigrades landed on the moon with the crashed Genesis. As we all know, tardigrades are extremely strong creatures that can not only survive temperatures close to absolute zero (-273°C) and temperatures as high as 151°C, but can also survive in extreme environmental conditions such as vacuum and radiation. Spivak said nonchalantly that these tardigrades "are nothing but a poetic 'signature' from the Earth." But people still began to worry that the moon, which originally had no life, would be contaminated by this "strongest creature on the surface of the earth."

From the photos taken by the Lunar Reconnaissance Orbiter (LRO), the crashed Beresheet directly smashed a hole on the lunar surface. Although scientists have long known that tardigrades can survive under a hydrostatic pressure of up to 7.5GPa , after all, this time it fell from the air with the lander. At the moment of impact with the lunar surface, the tardigrades were subjected to extremely high shock pressure. Can it really survive?

Photos of the lunar surface before and after the Genesis crash. Image credit: NASA

Let the tardigrades fly for a while

With such questions, a team from the University of Kent in the UK began to conduct experiments to study whether tardigrades can withstand such high-intensity impacts. They planned to use air guns to shoot bullets into the sand to simulate the scene of tardigrades riding on the Genesis to hit the moon.

However, the researchers did not use the air pistols or air rifles we see in sports competitions, but a special two-stage light air gun. The speed of ordinary air gun bullets usually does not exceed 500 meters per second, but the two-stage light air gun at the University of Kent can be adjusted at any speed between 0.3 kilometers per second and 7.5 kilometers per second.

In order to simulate the environment of different celestial bodies in the universe, researchers can also use liquid nitrogen to cool the target of the bullet to 100K (about -173°C) or heat it to 1000K (about 727°C). Using such an advanced air gun to launch a water bear that is no longer than 1 mm can be regarded as "shooting a mosquito with a cannon". Of course, such advanced gadgets are very difficult to use, and at most only two bullets can be fired a day.

The two-stage light gas gun of the University of Kent. Image source: original paper

Next, the tardigrades will enter the "bullet chamber". The researchers first fed the tardigrades with mineral water and moss, and then placed the well-fed little guys into the bottom of hollow nylon bullets. The bullets were filled with water, and there were 2 to 3 tardigrades in each bullet. In this way, when the bullet hit the sand, each tardigrade would be evenly impacted.

The staff then put the bullets in a freezer and froze them for 48 hours. In this case, the tardigrades enter a hibernation state called "tun" : their bodies dehydrate, shrink into a small ball that looks lifeless, and their metabolism drops to 0.1% of normal levels. However, once thawed, they can resume activity within 8 to 9 hours.

"Bang! Bang!" One after another, bullets carrying tardigrades shot straight towards the sand a few meters away.

The researchers tested six different shooting speeds from 0.5 km/s to 1.0 km/s, with corresponding peak shock wave pressures ranging from 0.61 GPa to 1.31 GPa. After each shooting, the researchers poured the sand with the bullets buried into the water, removed the sand by flotation, and then observed the recovery of the tardigrades.

The results showed that when the bullet's firing speed was no higher than 0.7 km/s (corresponding to a peak shock wave pressure of 0.86 GPa), all the tardigrades would slowly wake up; but when the firing speed reached 0.8 km/s (corresponding to a peak shock wave pressure of 1.01 GPa), only 60% of the tardigrades could recover; once the bullet speed reached 0.9 km/s (corresponding to a peak shock wave pressure of 1.14 GPa), not only did no tardigrades survive, but they were even broken into pieces. Moreover, all the tardigrades that had undergone this test took several times longer than their normal counterparts to recover from the "tun" state.

Water bears before and after the test. Figures a and b: Water bears before the test; Figure c: Water bears that successfully recovered after the test; Figure d: Water bears that were smashed into pieces during the test (Image source: original paper)

When the metal frame of the Beresheet hit the lunar surface, the shock wave pressure generated was far greater than 1.14GPa. The tiny bodies of these tardigrades must have been greatly shocked. "We can confirm that they did not survive," said Alejandra Traspas, one of the participants in the study, who issued a "death certificate" to the tardigrades on the Beresheet.

Where does life come from and where does it go?

In the 5th century BC, the ancient Greek philosopher Anaxagoras proposed that life is spread throughout the universe and carried everywhere by space dust, meteors, etc. This hypothesis is also called panspermia . Since this directly involves the origin of life, many scientists are studying whether life can be successfully transferred to Earth through meteorites, and whether life on Earth will settle elsewhere with the debris of the Earth.

Some studies have suggested that the debris produced by a violent impact on the Earth is fast enough to fly to the Moon. Calculations show that the average vertical speed of such debris hitting the Moon is 1.3 km/s, and the peak shock wave pressure exceeds 2GPa , which is higher than the strength that tardigrades can withstand. It seems that the "strongest creature on Earth" probably cannot settle on the Moon in this way.

The research team at the University of Kent also used the same two-stage light air gun to accelerate frozen yeast spores to a speed close to the upper limit of the air gun - 7.4 km/s, so that the spores in the vertically incident water would be subjected to a peak shock wave pressure of about 43GPa. The researchers were surprised to find that some yeasts were able to grow and reproduce again. Although, in this extreme case, the survival rate of yeast spores is only 0.001%. But compared to the tardigrades that will be broken into pieces at a collision of 0.9 km/s, the yeast spores impacted at 1.0 km/s can still have a 50% survival rate, which is also amazing.

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However, if we want to explore whether life can be transferred between celestial bodies, in addition to the peak shock wave pressure when impacting the moon, there are many other factors to consider. For example, whether the pressure on the earth when it is hit violently is too great, and whether the impact produces a high temperature that life cannot withstand. Therefore, even the most powerful life form would still find it difficult to survive such a test.

The origin of life is indeed like a "miracle". Although science has repeatedly told us that the possibility of life on Earth originating from other planets is extremely small, we can still have a beautiful fantasy: perhaps those tardigrades riding the "roller coaster" to the moon are dreaming sweet dreams.

Cute tardigrades. Image source: Wikimedia Commons

References

[1]https://davidson.weizmann.ac.il/en/online/sciencepanorama/what-happened-beresheet

[2]https://static1.squarespace.com/static/5c3bcbd5e17ba3597ea81282/t/5cbde30b6e9a7f176344d8a1/1555948311129/Overview+of+the+Lunar+Library.pdf

[3]https://en.wikipedia.org/wiki/Arch_Mission_Foundation

[4]https://www.wired.com/story/a-crashed-israeli-lunar-lander-spilled-tardigrades-on-the-moon/

[5]https://www.archmission.org/technologies

[6]https://www.archmission.org/spaceil

[7]https://link.springer.com/chapter/10.1007/978-94-007-1896-8_12

[8]https://www.liebertpub.com/doi/10.1089/ast.2020.2405

[9]https://www.sciencedirect.com/science/article/pii/S1877705817343333?via%3Dihub

[10]https://www.science.org/content/article/hardy-water-bears-survive-bullet-impacts-point

[11]https://en.wikipedia.org/wiki/Panspermia

[12]https://www.sciencedirect.com/science/article/pii/S0019103512004447?via%3Dihub

Planning and production

Source: Global Science

Author: Huang Yujia

Proofreading | Erqi

Editor｜Yang Yaping

The cover image and the images in this article are from the copyright library

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