WILL TARDIGRADES COLONIZE THE MOON ?

Everything was going as planned when suddenly on April 11, the probe experienced a problem with its propulsion as it began its descent. The speed was too great to slow down enough so that it crashed at over 3,000 km/h into our satellite

What happened to the tardigrades after the crash ? 

Are some still viable, buried under regolith, lunar dust whose depth varies from a few meters to a few tens of meters ?

Animals proof against almost anything

Tardigrades, these tiny creatures, occupy a unique place in the animal kingdom. Their size of less than a millimeter in no way reflects their remarkable complexity. Equipped with two eyes and a neuronal structure, they also have a mouth orifice at the end of a retractable proboscis, an intestine housing a microbiota, and four pairs of legs devoid of joints but equipped with sharp claws.

Their relationship with arthropods, such as insects and arachnids, is undeniable, testifying to a common evolutionary past.
Although most tardigrades live in aquatic environments, their presence is felt in all environments, including the most inhospitable of urban areas.
These beings fascinate mainly because of their incredible ability to withstand extreme conditions, far surpassing those encountered on Earth or the Moon. They can suspend their metabolism, losing up to 95% of their body water without apparent harm.

Some produce trehalose, an antifreeze sugar, while others synthesize proteins that transform cellular constituents into a glassy matrix, providing vital protection.
Dehydration causes a dramatic reduction in their size, sometimes up to half, with the legs disappearing, leaving only claws.

In this state, called cryptobiosis, they patiently wait for more lenient conditions to return to life.
However, specimens vary in their ability to withstand this desiccation, and not all are capable of resuscitation. Adult tardigrades can survive several minutes at extreme temperatures, reaching up to –272°C or 150°C, and are resistant over the long term to gamma ray doses of up to 1000 or 4400 Gray (Gy) , depending on the species. This unparalleled ability to survive defies the limits of biology and continues to amaze scientists to this day.

But difficulties...to survive

First of all, they must have survived the impact. Laboratory tests showed that frozen specimens of the species Hypsibius dujardini were intact after a vacuum impact at 2600 km/h on sand but were mutilated above 3000 km/h.

They must then resist the absence of water and withstand a cold of –170 to -190°C during the lunar night and a heat of 100 to 120°C during the day. A lunar day or night lasts a long time, a little less than 15 Earth days. Even the probe was not designed to withstand such amplitudes and had to cease all activity after only a few Earth days.

Finally, the surface of the Moon is not protected from solar particles and cosmic rays, particularly gamma rays. But there the tardigrades would be able to resist. Indeed, Robert Wimmer-Schweingruber, Professor at the University of Kiel in Germany, and his team showed that the doses of gamma rays striking the lunar surface were permanent but low compared to the doses cited previously. According to him, 10 years of exposure to gamma rays would correspond to a total dose of around 1 Gy.

Regardless, without water, oxygen or microalgae, the tardigrades will never be able to reactivate. Thus the colonization of the Moon by these animals is impossible. But specimens are on lunar soil and their presence raises ethical questions, as Matthew Silk, an ecologist at the University of Edinburgh, points out. Among these questions, there is one on the scientific level.

At a time when space exploration is taking off again in all directions, will contaminating other planets make us lose the possibility of looking for extraterrestrial life ?