from
https://www.sciencealert.com/space-accident-means-tardigrades-may-have-contaminated-the-moon

Space Accident Means Tardigrades May Have Contaminated The Moon
SPACE
02 March 2024
ByLAURENT PALKA, THE CONVERSATION
Crumpled looking tardigrade lying on its back with its feet in the air.
(David Spears FRPS FRMS/Corbis Documentary/Getty Images)
Just over five years ago, on 22 February 2019, an unmanned space probe
was placed in orbit around the Moon.

Named Beresheet and built by SpaceIL and Israel Aerospace Industries, it
was intended to be the first private spacecraft to perform a soft
landing. Among the probe's payload were tardigrades, renowed for their
ability to survive in even the harshest climates.

The mission ran into trouble from the start, with the failure of "star
tracker" cameras intended to determine the spacecraft's orientation and
thus properly control its motors. Budgetary limitations had imposed a
pared-down design, and while the command center was able to work around
some problems, things got even trickier on 11 April, the day of the landing.

On the way to the Moon the spacecraft had been travelling at high speed,
and it needed to be slowed way down to make a soft landing.
Unfortunately during the braking manoeuvre a gyroscope failed, blocking
the primary engine.

At an altitude of 150 m, Beresheet was still moving at 500 km/h, far too
fast to be stopped in time. The impact was violent – the probe shattered
and its remains were scattered over a distance of around a hundred
metres. We know this because the site was photographed by NASA's LRO
(Lunar Reconnaissance Orbiter) satellite on 22 April.

Beresheet crash site spotted by LRO 02

Animals that can withstand (almost) anything
So what happened to the tardigrades that were travelling on the probe?
Given their remarkable abilities to survive situations that would kill
pretty much any other animal, could they have contaminated the Moon?
Worse, might they be able to reproduce and colonize it?

Tardigrades are microscopic animals that measure less than a millimetre
in length. All have neurons, a mouth opening at the end of a retractable
proboscis, an intestine containing a microbiota and four pairs of
non-articulated legs ending in claws, and most have two eyes. As 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 ones. Emmanuelle Delagoutte, a researcher at
the CNRS, collects them in the mosses and lichens of the Jardin des
Plantes in Paris.

To be active, feed on microalgae such as chlorella, and move, grow and
reproduce, tardigrades need to be surrounded by a film of water. They
reproduce sexually or asexually via parthenogenesis (from an
unfertilised egg) or even hermaphroditism, when an individual (which
possesses both male and female gametes) self-fertilises.

Once the egg has hatched, the active life of a tardigrade lasts from 3
to 30 months. A total of 1,265 species have been described, including
two fossils.

Tardigrades are famous for their resistance to conditions that exist
neither on Earth nor on the Moon. They can shut down their metabolism by
losing up to 95% of their body water. Some species synthesise a sugar,
trehalose, that acts as an antifreeze, while others synthesise proteins
that are thought to incorporate cellular constituents into an amorphous
"glassy" network that offers resistance and protection to each cell.

During dehydration, the tardigrade's body can shrink to half its normal
size. The legs disappear, with only the claws still visible. This state,
known as cryptobiosis, persists until conditions for active life become
favourable again.

Depending on the species of tardigrade, 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 over the long
term at high doses of gamma rays of 1,000 or 4,400 Gray (Gy).

By way of comparison, a dose of 10 Gy is fatal for humans, and 40-50,000
Gy sterilises all types of material. However, whatever the dose,
radiation kills tardigrade eggs. What's more, the protection afforded by
cryptobiosis is not always clear-cut, as in the case of Milnesium
tardigradum, where radiation affects both active and dehydrated animals
in the same way.

The species Milnesium tardigradum in its active state. (E. Schokraie, U.
Warnken, A. Hotz-Wagenblatt, M.A. Grohme, S. Hengherr, et al. (2012).,
CC BY)
Lunar life?
So what happened to the tardigrades after they crashed on the Moon? Are
any of them still viable, buried under the moon's regolith, the dust
that varies in depth from a few metres to several dozen metres?

First of all, they have to have survived the impact. Laboratory tests
have shown that frozen specimens of the Hypsibius dujardini species
travelling at 3,000 km/h in a vacuum were fatally damaged when they
smashed into sand. However, they survived impacts of 2,600 km/h or less
– and their "hard landing" on the Moon, unwanted or not, was far slower.

The Moon's surface is not protected from solar particles and cosmic
rays, particularly gamma rays, but here too, the tardigrades would be
able to resist.

In fact, Robert Wimmer-Schweingruber, professor at the University of
Kiel in Germany, and his team have shown that the doses of gamma rays
hitting the lunar surface were permanent but low compared with the doses
mentioned above – 10 years' exposure to Lunar gamma rays would
correspond to a total dose of around 1 Gy.

But then there's the question of "life" on the Moon. The tardigrades
would have to withstand a 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 wasn't designed to withstand such extremes and even if it
hadn't crashed, it would have ceased all activity after just a few Earth
days.

Unfortunately for the tardigrades, they can't overcome the lack of
liquid water, oxygen and microalgae – they would never be able to
reactivate, much less reproduce. Their colonising the Moon is thus
impossible.

Still, inactive specimens are on lunar soil and their presence raises
ethical questions, as Matthew Silk, an ecologist at the University of
Edinburgh, points out. 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 author thanks Emmanuelle Delagoutte and Cédric Hubas of the Muséum
de Paris, and Robert Wimmer-Schweingruber of the University of Kiel, for
their critical reading of the text and their advice.

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