Experts believe that the conditions on the Moon are too extreme even for tardigrades, the organisms known for their resilience.
More than five years ago, on February 22, 2019, an unmanned spacecraft entered lunar orbit. Named Beresheet, the spacecraft was developed by SpaceIL and Israel Aerospace Industries, and it gently landed on the Moon carrying cargo that included tardigrades, famous for their ability to survive in the harshest climates, according to IFL Science.
The likelihood of tardigrades colonizing the Moon is nearly impossible. (Image: Techno Science).
The mission faced difficulties from the start due to issues with the camera used for navigation and spacecraft motor adjustments. Budget constraints led to cutbacks in design. While the control center worked to resolve the issues, things became more complicated on the landing day, April 11, 2019. On the way to the Moon, the spacecraft traveled at high speeds and needed to slow down for a gentle landing. During the deceleration, a gyroscope malfunctioned, causing the main engine to fail. At an altitude of about 150 meters, Beresheet was still moving at 500 km/h, too fast to stop in time. This resulted in a violent crash, shattering the probe and scattering debris within a 100-meter radius of the impact site. So, what happened to the tardigrades on board? Do they have the potential to reproduce and colonize the Moon?
Tardigrades are microscopic organisms measuring less than one millimeter in length. All tardigrades have neurons, a mouth at the end of a retractable snout, a gut containing a microbiome, four pairs of unjointed legs with claws at the end, and two eyes. Despite their small size, they share a common ancestor with arthropods such as insects and spiders.
Most tardigrades live in aquatic environments, but they can be found in any habitat, even urban areas. Emmanuelle Delagoutte, a researcher at the French National Center for Scientific Research (CNRS), collects tardigrades from moss and lichen in the Jardin des Plantes botanical garden in Paris. To operate, feed on algae like Chlorella, and move, tardigrades need to be surrounded by a layer of water. They can reproduce sexually or asexually through parthenogenesis (from unfertilized eggs) or even hermaphroditically when an individual (possessing both male and female gametes) self-fertilizes. After hatching, the lifespan of a tardigrade ranges from 3 to 30 months. Researchers have described a total of 1,265 tardigrade species, including two fossils.
Tardigrades are renowned for their ability to withstand extreme conditions. They can halt their metabolism by reducing their body water content by 95%. Some species synthesize trehalose, which acts as an antifreeze, while others produce proteins that combine cellular components into an amorphous network that protects each cell. During dehydration, the tardigrade’s body shrinks to half its normal size. Their legs disappear, leaving only the claws visible. This state, known as cryptobiosis, persists until they encounter favorable living conditions.
Depending on the species, tardigrades may require varying amounts of time to dehydrate, and not all specimens of the same species can return to normal life. Mature dehydrated tardigrades can survive for several minutes at temperatures as low as -272 degrees Celsius or as high as 150 degrees Celsius and endure gamma radiation doses of 40,000 – 50,000 Gy over extended periods. However, regardless of the dose, radiation can kill tardigrade eggs. Additionally, in the case of the species Milnesium tardigradum, radiation affects both dehydrated individuals and normal individuals equally.
What happened to the tardigrades after the spacecraft carrying them crashed into the Moon? Did any individuals survive, buried under layers of lunar dust several meters to tens of meters deep? Laboratory tests have shown that frozen specimens of the species Hypsibius dujardini moved at speeds of 3,000 km/h in a vacuum chamber but died when they crashed into a sand layer. However, they survived the impact force at speeds of 2,600 km/h or lower, and the probe’s hard landing on the Moon was much slower.
The lunar surface lacks a protective layer against solar particles and cosmic rays, especially gamma rays, but tardigrades can withstand this. In fact, Robert Wimmer-Schweingruber, a professor at the University of Kiel in Germany, and his colleagues demonstrated that the gamma radiation reaching the lunar surface is quite low. The level of gamma radiation exposure on the Moon over 10 years corresponds to a dose of approximately 1 Gy.
Next, tardigrades would have to endure conditions of water scarcity as well as temperature fluctuations ranging from -170 to -190 degrees Celsius during the lunar night and from 100 to 120 degrees Celsius during the day. A lunar day or night lasts approximately 15 Earth days. The probe was not designed to withstand such extreme temperature fluctuations. Even without crashing, the vessel would cease all operations after just a few Earth days. Tardigrades cannot survive the lack of liquid water, oxygen, and algae. They would never be able to reactivate and would be even less likely to reproduce. Therefore, the colonization of the Moon by tardigrades is impossible.
