A new study points out that the methane tail gas released during the ignition and landing process of future lunar landing missions may spread to the coldest and most scientifically valuable permanent shadow areas at the lunar poles in a very short time, thereby "contaminating" chemical clues related to the origin of life on Earth that have been preserved there for billions of years. Models show that it takes less than two synodic months for methane molecules to jump from one pole to the other, and about half of them will eventually be deposited in the cold depressions at the poles, directly mixed with ancient ice layers that are regarded as the "original chemical archives."
The study, published in the Journal of Geophysical Research: Planets and led by European Space Agency (ESA) planetary protection officer Silvio Sinibaldi and physicist Francesca Paiva, focuses on a core question: As governments, commercial companies and various organizations launch a new wave of lunar landings, whether human activities are inadvertently rewriting or even erasing key evidence on the origin of life on the moon. The research team believes that when formulating the lunar mission plan, "protection of the lunar environment and scientific archives" must be included in the scope of planetary protection, otherwise a large amount of precious original information may be "covered" by humans themselves in the next few decades.
The scientific community has always attached great importance to the permanent shadow areas at the poles of the moon. These impact craters, which are shielded from direct sunlight all year round, are believed to contain ice and organic matter brought by comet and asteroid impacts billions of years ago. They may include "prebiotic organic molecules", that is, chemicals that can evolve into the earliest building blocks of life under the right conditions. Since long-term geological activities and erosion on the earth have almost erased such ancient chemical records, these extremely cold areas of the moon have become natural laboratories for tracing the chemical beginnings of life. Once mixed with modern exhaust gas components, the originally extremely weak and precious signals may be obscured.
To assess the risk of contamination, Paiva and his colleagues built a high-precision numerical model, taking the European Space Agency's "Argonaut" lunar lander as a case study, to simulate the migration and deposition behavior of methane, the main organic component in the exhaust, on the lunar surface when it landed at the lunar south pole. Different from previous studies on the migration of water molecules, this model systematically considers the movement of organic molecules in the ultra-thin environment of the moon for the first time, and also incorporates the effects of solar wind, ultraviolet radiation and other factors on methane distribution and lifetime, so it is closer to the actual mission scenario.
Simulation results show that the methane molecules released during the landing stage will fly ballistically on the lunar surface like "bouncing balls", with almost no atmospheric resistance and only jumping to the ground under the influence of gravity to span a huge distance. Under the alternating effects of sunlight heating and shadow cooling, these molecules can "jump" from the South Pole to the North Pole in less than two synodic months, and in about seven synodic months (equivalent to nearly seven months on Earth), more than half of the tail gas methane is "cold trapped" in the low-temperature areas of the two poles, of which about 42% is deposited in the Antarctic and 12% is deposited in the North Pole.
What surprised the researchers was the time scale of the process—in just a week or so (on the scale of a lunar day), molecules can spread globally from pole to pole, meaning that there are few landing sites that are completely safe and free of remote contamination. Paiva pointed out that on the near-vacuum lunar surface, methane molecules do not collide and scatter as frequently as they do in the Earth's atmosphere. Instead, they are heated in the sunlit area, cooled in the shadowed area, and gradually captured along a simple parabolic trajectory, making "any landing an input of exogenous matter into the entire lunar environment."
However, the study also believes that humans still have some room to slow down this trend. For example, by giving priority to cooler landing areas, the exhaust gas may be limited to a smaller range to a certain extent, or by reducing organic pollutant emissions from combustion through mission design. One idea proposed by Sinibaldi is that in the future, we can focus on studying whether exhaust gas molecules are only deposited on the surface of the permanently shadowed ice layer without going deep into the interior. If it can be confirmed that the "contamination layer" only covers the surface, then scientific detection can bypass the interference of human activities by drilling deeper samples.
Both researchers emphasized the need for a systematic assessment of the behavior of different classes of molecules, not just methane, supported by more models and future field measurements. Paiva plans to further study other potential sources of contamination from the spacecraft body, such as molecules released from materials such as paint and rubber. These components may also be cold trapped in the polar regions, bringing additional noise to the analysis of original organic matter.
On Earth, humans have established special regulations to prevent pollution and over-exploitation in areas such as Antarctica and national parks, and researchers believe that the scientific and environmental value of the moon is no less valuable than these protected areas. Sinibaldi called for similar protection ideas to be introduced into lunar landing planning as early as possible, and for the upcoming missions to be equipped with necessary monitoring instruments to "check the model while exploring." Otherwise, humans may inadvertently erase the moon's "archives of the origin of life" before truly understanding them.
Compiled from /ScitechDaily