Abstract EANA2025-139

Experimental verification of the panspermia hypothesis—which assumes the interplanetary transfer of microorganisms—and clarification of how terrestrial life can survive and adapt in deep space environments are important issues in astrobiology. These issues also form the scientific basis for future space exploration, space agriculture, and planetary protection policies.

Since 2008, a series of space exposure experiments have been conducted using the exposure facility on the International Space Station (ISS) [1]. The experiments have targeted microorganisms and organic compounds, and they have been given the series name "Tanpopo." One notable finding was that dried cell pellets (approximately 109 cells) of the radiation-resistant bacterium Deinococcus radiodurans could potentially survive for the equivalent of approximately 50 years in space under shaded conditions, providing valuable insight into the long-term survival of microbes in space [2]. However, the ISS is located at low Earth orbit (LEO), which is shielded by Earth's magnetosphere. This environment differs significantly from deep space, particularly with regard to the type and intensity of radiation, as well as other environmental factors.

To experimentally examine the effects on the microorganisms by longest stage of interplanetary transfer—transfer in the deep space—in the panspermia, it is necessary to conduct exposure experiments in environments closer to deep space—namely, beyond Earth’s magnetosphere, such as the lunar surface or the Lunar Orbital Platform-Gateway. Additionally, as planetary exploration intensifies, the potential for unintentional contamination of extraterrestrial bodies by Earth-originating microbes is becoming a growing concern in planetary protection, necessitating scientific evaluation of such risks.

This study proposes a short-duration space exposure experiment on the lunar surface, aiming to analyze the survivability and molecular responses of microorganisms and spores of moss plant. Target organisms include bacteria (D. radiodurans, Bacillus atrophaeus, Escherichia coli, Nostoc sp. HK-01), a eukaryotic microbe (Schizosaccharomyces pombe), and a moss plant (Physcomitrium patens), covering a broad phylogenetic range. The exposure apparatus will be designed based on the proven "TANPOPO" hardware and assumes post-exposure sample return.

By placing samples in both sunlit and permanently shadowed regions of the lunar polar area, the experiment will allow for the evaluation of multiple factors—such as ultraviolet radiation, cosmic radiation, extreme low temperatures, and vacuum—either individually or in combination. Post-exposure analyses will go beyond simple survivability and will include assessments of DNA damage, mutation frequency and spectrum, transcriptomics, proteomics, and metabolomics, to comprehensively understand how the space environment affects molecular biological systems.

This report presents the conceptual design and current preparation status of the proposed experiment.

 

References

[1] Yamagishi, A., et al. (2021) Scientific targets of Tanpopo: Astrobiology exposure and micrometeoroid capture experiments at the Japanese Experiment Module Exposed Facility of the International Space Station. Astrobiol. 21(12): 1451-1460

[2] Kawaguchi, Y., et al. (2020) DNA damage and survival time course of deinococcal cell pellets during 3 years of exposure to outer space. Front. Microbiol. 11: 2050. doi: 10.3389/fmicb.2020.02050