Thousands of microscopic animals called tardigrades are likely scattered across the surface of the Moon. These creatures, also known as water bears, are known for their ability to withstand extreme environments. In 2019, a mission carrying a payload of these organisms crash-landed, leaving their fate on the lunar surface a subject of scientific interest and debate about depositing Earth-based life on other celestial bodies.
The Beresheet Incident
The tardigrades traveled to the Moon on the Israeli Beresheet mission, the first private lunar landing attempt. Launched in February 2019, the spacecraft carried a “lunar library” from the Arch Mission Foundation, an archive with 30 million pages of human history and DNA samples. The tardigrades were a late addition to this payload. Thousands of the creatures were dehydrated into a state of suspended animation and sealed in a resin layer protecting the library. On April 11, 2019, as the Beresheet lander attempted its final descent, its main engine failed, and the spacecraft crashed onto the lunar surface, scattering its contents in the Sea of Serenity.
Survival in the Lunar Environment
The tardigrades arrived in a dormant state known as cryptobiosis, where their metabolic processes are almost completely suspended. This state allows them to endure the lunar environment, which has a near-total vacuum, intense radiation, and temperature fluctuations from over 120°C (248°F) to below -170°C (-274°F). While the impact’s shock pressure may have been greater than what tardigrades have been known to survive, scientists believe some endured, protected within the resin.
Even if they survived the crash, the tardigrades cannot revive or reproduce on the Moon. To exit their dormant state, they require liquid water, which is absent on the lunar surface, leaving them trapped and inert.
Planetary Protection Concerns
The dispersal of tardigrades on the Moon sparked a conversation about planetary protection. This principle is an international agreement to prevent the biological contamination of other celestial bodies and protect Earth from potential extraterrestrial life. The Beresheet incident highlighted a gap in these protocols, as private missions may not be subject to the same sterilization guidelines as government agencies.
A primary concern is avoiding “false positives” in the search for extraterrestrial life, as discovering Earth-based organisms could confuse the search for alien biomarkers. The Outer Space Treaty does not explicitly forbid payloads like the lunar library, and the crash has prompted calls for clearer global rules for all future missions.