Beresheet, Tardigrades and the Moon: Could They Survive?

Beresheet’s failed landing on the Moon

A little more than five years ago, on 22 February 2019, an uncrewed space probe entered orbit around the Moon.

Called Beresheet, the craft was made by SpaceIL and Israel Aerospace Industries and was intended to become the first privately developed spacecraft to achieve a soft landing. Its payload included tardigrades, creatures renowned for surviving even the most extreme environments.

Problems affected the mission from the outset. The "star tracker" cameras, which were meant to establish the spacecraft’s orientation and enable correct motor control, failed. Financial constraints had resulted in a simplified design and, although the control centre managed to overcome certain difficulties, the situation became more complicated on 11 April, the planned landing day.

Having travelled towards the Moon at great speed, the spacecraft needed to slow dramatically to land gently. During the braking manoeuvre, however, a gyroscope malfunctioned and prevented the main engine from operating.

At a height of 150 m, Beresheet was still travelling at 500 km/h, much too quickly to stop in time. The collision was severe: the probe broke apart, scattering debris across roughly a hundred metres. NASA’s LRO (Lunar Reconnaissance Orbiter) satellite photographed the crash site on 22 April, providing this evidence.

Tardigrades and their extraordinary resilience

What, then, became of the tardigrades carried by the probe? Since they can survive circumstances that would kill almost any other animal, could they have contaminated the Moon? More alarmingly, could they reproduce there and establish a colony?

Tardigrades are microscopic animals, measuring under a millimetre long. Each has neurons, a mouth at the tip of a retractable proboscis, an intestine containing microbiota, and four pairs of unjointed legs ending in claws; most also possess two eyes. Despite their tiny size, they share an ancestor with arthropods including insects and arachnids.

Although most tardigrades inhabit aquatic settings, they occur in every type of environment, including cities. Emmanuelle Delagoutte, a CNRS researcher, gathers them from mosses and lichens in Paris’s Botanical Garden.

For tardigrades to be active, feed on microalgae such as chlorella, move, grow and reproduce, they must be surrounded by a thin layer of water. They can reproduce sexually, or asexually through parthenogenesis, from an unfertilised egg, and even by hermaphroditism, whereby an individual containing both male and female gametes fertilises itself.

From active life to cryptobiosis

After hatching, a tardigrade’s active lifespan ranges from 3 to 30 months. Scientists have described 1,265 species in total, two of which are fossils.

Tardigrades are celebrated for withstanding conditions found neither on Earth nor on the Moon. By losing as much as 95% of their bodily water, they can suspend their metabolism. Some species produce trehalose, a sugar that functions as an antifreeze, while others create proteins believed to arrange cellular components within an amorphous "glassy" network, providing each cell with strength and protection.

When dehydrating, a tardigrade can contract to half its usual size. Its legs vanish from view, leaving only the claws visible. This condition, called cryptobiosis, continues until conditions again permit active life.

The time required for dehydration differs between tardigrade species, and not every member of a species succeeds in returning to an active state. Dehydrated adults can withstand temperatures from -272°C to 150°C for several minutes, and can tolerate, over longer periods, gamma-radiation doses of 1,000 or 4,400 Gray (Gy).

For comparison, humans die after a dose of 10 Gy, while 40-50,000 Gy sterilises every kind of material. Yet radiation destroys tardigrade eggs at any dose. Furthermore, cryptobiosis does not always offer unambiguous protection: in Milnesium tardigradum, for example, radiation affects active and dehydrated animals equally.

Could tardigrades survive on the Moon?

So, after the lunar crash, what happened to the tardigrades? Could any remain viable beneath the Moon’s regolith, the dust layer whose depth ranges from a few metres to several dozen metres?

They would first have needed to survive the impact itself. Laboratory experiments found that frozen Hypsibius dujardini specimens moving through a vacuum at 3,000 km/h suffered fatal damage after striking sand. They did, however, survive impacts at 2,600 km/h or below - and their unintended "hard landing" on the Moon occurred at a considerably lower speed.

The lunar surface has no protection against solar particles or cosmic rays, especially gamma rays. Even so, tardigrades could endure these conditions.

Robert Wimmer-Schweingruber, a professor at Germany’s University of Kiel, and his team have shown that gamma-ray doses reaching the lunar surface are continuous but small when compared with the doses already cited. Ten years of exposure to lunar gamma rays would deliver a cumulative dose of approximately 1 Gy.

The remaining issue is whether there can be “life” on the Moon. The tardigrades would need to tolerate the absence of water, along with temperatures of -170 to -190°C during lunar night and 100 to 120°C during daytime.

A lunar day or night is lengthy, lasting just under 15 Earth days. Beresheet itself was not built to withstand such extremes and, even without crashing, would have stopped functioning after only a few Earth days.

Unfortunately for the tardigrades, the absence of liquid water, oxygen and microalgae is insurmountable. They could never reactivate, let alone reproduce. Colonisation of the Moon is therefore impossible.

Nevertheless, inactive specimens now lie on lunar ground, and their presence poses ethical questions, as Matthew Silk, an ecologist at the University of Edinburgh, has observed. In addition, as space exploration expands in every direction, contaminating other planets may deprive us of the chance to detect extraterrestrial life.

The author thanks Emmanuelle Delagoutte and Cédric Hubas of Paris’s National Museum of Natural History, and Robert Wimmer-Schweingruber of the University of Kiel, for critically reading the text and offering their advice.

Laurent Palka, Senior Lecturer, National Museum of Natural History (MNHN)

This article is republished from The Conversation under a Creative Commons licence. Read the original article.