A recent study indicates that over half of the methane exhaust from lunar spacecraft could contaminate areas of the moon, including polar regions that may contain evidence regarding the origins of life on Earth. This potential contamination is projected to occur rapidly, with methane molecules capable of traversing the lunar surface from the South Pole to the North Pole in less than two lunar days, regardless of the spacecraft's landing site.
Background: Intensifying Lunar Exploration
With increasing interest in lunar exploration from governmental, private, and non-governmental entities, understanding the environmental impact of missions is considered relevant for scientific research. This knowledge is intended to inform the development of planetary protection strategies for the lunar environment and contribute to the design of missions aimed at minimizing environmental impact.
Silvio Sinibaldi, a planetary protection officer at the European Space Agency and a senior author of the study, emphasized the importance of safeguarding scientific inquiry and investment in space. He noted that the moon serves as a natural environment for scientific discovery, and current activities could potentially impede future scientific exploration.
Significance for Scientific Research
At the lunar poles, permanently shadowed regions (PSRs) contain ice deposits. Scientists hypothesize these deposits may hold materials, including "prebiotic organic molecules," delivered to the moon and Earth by comets and asteroids billions of years ago. Prebiotic organic molecules are considered key components that could have formed the original building blocks of life, such as DNA, under specific conditions. Discovering these molecules in their original state could enable researchers to study the mechanisms behind the emergence of life on Earth.
Earth's dynamic surface is believed to have erased traces of these original molecules. In contrast, parts of the moon's surface have remained largely unaltered for billions of years, potentially preserving a clearer record, particularly within PSRs where low temperatures can facilitate molecule accumulation. However, molecules released by lunar spacecraft could also accumulate in these regions, potentially obscuring pristine evidence of life-originating materials.
Study Methodology
The study, titled "Can Spacecraft-Borne Contamination Compromise Our Understanding of Lunar Ice Chemistry?" and published in the Journal of Geophysical Research: Planets, utilized a computer model. The model was developed by Sinibaldi and Francisca Paiva, a physicist at Instituto Superior Técnico and the lead author.
The model simulated the dispersion of methane, a primary organic compound released during the combustion of Argonaut mission propellants, across the lunar surface following a simulated landing at the moon's South Pole. While prior research focused on water molecule movement on the moon, this study specifically focused on organic molecules like methane and incorporated the effects of solar wind and UV radiation on methane behavior.
Paiva noted the computational intensity involved in modeling thousands of molecules, their movements, collisions, and surface interactions, with individual simulations lasting days or weeks.
Key Findings
The model predicted that exhaust methane would reach the North Pole in under two lunar days. Within seven lunar days (approximately seven Earth months), over 50% of the total exhaust methane was "cold trapped" at the frigid poles, with 42% at the South Pole and 12% at the North Pole.
The rapid distribution is attributed to the moon's near-absence of an atmosphere, which allows methane molecules to traverse the landscape unimpeded by other molecules. Paiva explained that the trajectories are primarily ballistic, meaning molecules hop across the surface. This suggests that establishing landing sites entirely impervious to exhaust molecule dispersal may be challenging, as the study indicated molecules could travel across the entire lunar surface, potentially leading to widespread contamination regardless of the landing location.
Future Research and Mitigation Strategies
While widespread contamination is projected, potential mitigation strategies are being considered. Paiva suggested that colder landing sites might contain exhaust molecules more effectively than warmer ones. Sinibaldi also proposed investigating whether exhaust molecules might settle on the icy surfaces of PSRs, leaving underlying materials unaffected for research purposes.
The authors emphasized the need for confirmation of these results through additional simulations and direct measurements on the moon. Sinibaldi expressed interest in engaging mission teams to ensure instruments are included on future missions to validate these models. Paiva also plans to investigate the potential risks posed by other molecules originating from spacecraft hardware, such as paint and rubber.