An Israeli space probe landed these animals on the moon and they may still be alive.

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Just over five years ago, on February 22, 2019, the Beresheet space probe, built by SpaceIL and Israel Aerospace Industries, entered lunar orbit. Beresheet was to be the first private spacecraft to make a soft landing on the lunar surface. Among the probe's payload were thousands of tardigrades, tiny animals known for their extraordinary ability to survive in the most extreme conditions.

tardigrades luna

On the way to the Moon, the spacecraft had been traveling at high speed and needed to be braked for a soft landing. Unfortunately, during the braking maneuver, a gyroscope failed, locking the primary engine. At 150 m altitude, Beresheet was still moving at 500 km/h.too fast to stop in time.

The impact was violent: the probe was shattered and its debris was scattered about a hundred meters away. We know this because the LRO satellite (Lunar Reconnaissance Orbiter) photographed the impact site shortly after the accident on April 22.

Beresheet crash site sighted by LRO 02

Animals that can withstand (almost) anything

What happened to the tardigrades who were traveling on the probe?

Given their extraordinary ability to survive situations that would kill almost any other animal, could they have contaminated the Moon? Worse, could they reproduce and colonize it?

Tardigrades are microscopic animals measuring less than a millimeter in length. They all have neurons, an open mouth at the end of a retractable proboscis, a gut containing a microbiota and four pairs of non-articulated legs ending in claws, and most have two eyes. Small as they are, they share a common ancestor with arthropods such as insects and arachnids.

Most tardigrades live in aquatic environments, but they can be found in any environment, even urban. Emmanuelle Delagoutteresearcher at the French National Center for Scientific Research, collects them in the mosses and lichens of the Jardin des Plantes of Paris.

To be active, to feed on microalgae such as chlorella, and to move, grow and reproduce, tardigrades need to be surrounded by a film of water. They reproduce sexually or asexually by parthenogenesis (from an unfertilized egg) or even hermaphroditism, when an individual (possessing both male and female gametes) self-fertilizes. Once the egg has hatched, the active life of a tardigrade lasts from 3 to 30 months. 1,265 species have been describedincluding two fossils.

Powers from another world

Tardigrades are famous for their resistance to conditions so extreme that they do not even exist on Earth or the Moon. They can lose up to 95 % of their body water to disrupt their metabolism. Some species synthesize a sugar, trehalose, which acts as an anti-freeze agentwhile others synthesize proteins that are believed to incorporate cellular constituents into an amorphous "glassy" network that provides strength and protection to each cell.

During dehydration, the tardigrade's body may shrink to half its normal size. The legs disappear and only the claws remain visible. This state, known as cryptobiosispersists until the conditions for active life become favorable again.

Depending on the tardigrade species, individuals need more or less time to dehydrate and not all specimens of the same species manage to return to active life. Dehydrated adults survive for a few minutes at temperatures as low as -272 °C or as high as 150 °C, and in the long term withstand high gamma doses of 1 000 or 4 400 Gray (Gy). By way of comparison, a dose of 10 Gy is lethal to humans and 40 to 50 000 Gy sterilizes all types of material. However, whatever the dose, radiation kills tardigrade eggs.

In addition, the protection offered by the cryptobiosis is not always clear, as in the case of Milnesium tardigradumThe species is affected by radiation in the same way in both active and dehydrated animals.

file 20240226 18 qtnl5g.png?ixlib=rb 1.1
The species Milnesium tardigradum in an active state. E. Schokraie, U. Warnken, A. Hotz-Wagenblatt, M.A. Grohme, S. Hengherr, et al. (2012)., CC BY

Lunar life?

What happened to the tardigrades after crashing into the Moon? Are any of them still alive, buried under the lunar regolith, the dust that varies in depth from a few meters to several tens of meters?

For this to be possible, they would have to have survived the impact in the first place. Laboratory tests have demonstrated that frozen specimens of the species Hypsibius dujardiniThe spacecraft, traveling at 3 000 km/h in a vacuum, suffer fatal damage when they crash into the sand. However, they survive impacts of 2 600 km/h or less, and their "crash landing" on the Moon was much slower.

The surface of the Moon is not protected from solar particles and cosmic rays, in particular gamma rays, but even in this case the tardigrades would be able to resist. In fact, Robert Wimmer-Schweingruber, professor at the University of Kiel (Germany), and his team have demonstrated that gamma ray doses impinging on the lunar surface are permanentbut low compared to the doses mentioned above: 10 years of exposure to lunar gamma rays would correspond to a total dose of about 1 Gy.

But there is still the key question of whether "life" on the Moon is possible. Tardigrades would have to endure the lack of water, as well as temperatures ranging from -170 to -190 °C during the lunar night and 100 to 120 °C during the day. A lunar day or night lasts a long time, just under 15 Earth days. The probe itself was not designed to withstand such extreme temperatures and, even if it had not crashed, it would have ceased all activity within a few Earth days.

Unfortunately for tardigrades, they cannot overcome the lack of liquid water, oxygen and microalgae, so they could never reactivate, let alone reproduce. Therefore, their colonization of the Moon is impossible.

Even so, dormant specimens on lunar soil are to be expected and their presence raises ethical issues, as noted by Matthew Silksaid an ecologist at the University of Edinburgh. Moreover, at a time when space exploration is taking off in all directions, contaminating other planets could mean that we would lose the opportunity to detect extraterrestrial life.The Conversation

Laurent PalkaMaître de conférences, Muséum national d'histoire naturelle (MNHN)

This article was originally published in The Conversation. read the original.