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The surface conditions on the Moon are clearly a harsh mistress of a world, with high doses of ultraviolet irradiation, wide temperature extremes and low pressure – then toss in high levels of ionizing radiation.

A new report takes a look at microbial survival on lunar spacecraft – even suggesting where best to go to capture microbes sent to the Moon onboard lunar spacecraft.

Model developed

A Lunar Microbial Survival (LMS) model was developed that estimates the total viable bioburden of all spacecraft landed on the Moon. The work was led by Andrew Schuerger at the University of Florida.

The research — A Lunar Microbial Survival Model for Predicting the Forward Contamination of the Moon – has been published in the journal, Astrobiology.

Although noteworthy articles have characterized microbial diversity of spacecraft before launch, almost no literature exists on how terrestrial microorganisms might survive the journey to the lunar surface or how long they might survive after delivery.

Soviet Union’s Luna-2.
Credit: NASA Space Science Data Coordinated Archive/GSFC

Landed, crashed missions

Since the Soviet Union’s Luna 2 spacecraft impacted the Moon on September 14, 1959, well over 54 missions have either landed or crashed on the lunar surface. The paper notes that 77 spacecraft, boosters, payloads, rovers, and other structures have made it to the surface of the Moon. But there has not been a systematic estimate compiled of the microbial bioburdens on all of this Moon-bound hardware.

“The primary reasons for developing the LMS model was to predict whether previously landed spacecraft might harbor viable bioburdens over time and identify for Earth return the most promising landed or crashed spacecraft hardware for future human missions,” the research paper explains.

Arrival of humans: 2030

The research paper says that LMS model predictions for 2030 (a reasonable date for the return of humans to the Moon) indicate that China’s Chang’e-3 lander/Yutu-1 rover is likely to retain significant numbers of viable bacteria, and only on deeply embedded surfaces.

Chang’e-4 farside mission – lander and Yutu-2 rover
Credit: CNSA/CLEP

“The newest Yutu rover would also be expected to have spores/cells surviving by January 1, 2030,” said Schuerger. “Also, there are other landers planned for the near future that have not yet been launched. I hope some of those teams add-in biological samples to be checked by a future astrobiologist collecting spacecraft parts in 2030,” he told Inside Outer Space.

NASA’s Surveyor III – new insight

Schuerger and his research colleagues also took note of the recovery of a single colony of Streptococcus mitis from foam insulation that was deeply embedded within the NASA Surveyor III camera recovered by Apollo 12 astronauts and brought back to Earth in November 1969.

Apollo 12’s visit to Surveyor III landing site.
Credit: NASA

During the Apollo 12 mission, astronauts Pete Conrad and Alan Bean piloted their lander Intrepid within ‏1,640 feet (500 meters) of the Surveyor III spacecraft that was present on the Moon for 942 days (31.9 “lunations”) from April 20, 1967 to November 20, 1969.

Some scientists have previously reported that a single pure culture of Streptomyces mitis was recovered from circuit board foam insulation that was deeply embedded within the Surveyor III camera body. However, later research points to that hardware not handled on return by appropriate aseptic protocols.

The research paper backs the view that “the most likely explanation of the presence of S. mitis in the single positive culture tube from the assayed Surveyor III equipment was through contamination during the post-landing processing of the camera.”

China’s lander/rover – bioburden experiment

According to the paper, the last 10 lunar spacecraft may have residual viable microorganisms that are deeply embedded near the central cores of each spacecraft.

For January 1, 2030, again, a reasonable date for the return of humans to the Moon), five of the last ten lunar spacecraft would be expected to harbor no viable microorganisms. Only the Chang’e/Yutu landers and rovers could plausibly harbor significant bioburdens on deeply embedded components. That is, a population of viable microbes that might be detected on returned spacecraft components.

For all earlier spacecraft landed or crashed between September 14, 1959 (Luna 2) and August 18, 1976 (Luna 24) the LMS model predicts them to be free of viable Earth microorganisms.

The first picture Neil Armstrong took during the Apollo 11 moonwalk shows a jettison bag under Eagle’s descent stage.
Credit: NASA

High-priority

The new paper concludes by spotlighting high-priority astrobiology targets for collecting lunar archived payloads and equipment for microbial study.

For example, the highest priority for an Apollo-era microbial survey would be the nylon jettison (JETT) bags placed underneath the lunar module (LM) descent stages or tossed onto the lunar surface before leaving the Moon.

The JETT bags contain disposable materials from within the crewed LM ascent stages before landing, including water containers, human waste, food wrappers, Lithium hydroxide canisters (for airborne spores), and sleep restraints.

“If the JETT bags with human waste and sleep restraints were placed under the LM descent stages,” the research paper asserts, “they would have the richest microbial bioburdens and species diversity of the accessible materials on the Moon (i.e., materials directly handled by human astronauts), and the bags have been mostly shielded from the worst of the thermal cycling conditions on the Moon. Furthermore, the LM descent stages are the largest intact structures on the Moon and would provide insights into shielding against ionizing radiation effects on biological systems.”

Picking up the trash – new assignment for future Moonwalkers!
Credit: NASA

Microbial survival

Lastly, the researchers suggest that any new lunar spacecraft landed or crashed to the lunar surface during the next decade should be fitted with astrobiology payloads that could be recovered and analyzed for microbial survival, biosignature degradation, and materials alterations when humans return to the Moon around 2030.

“Such astrobiological experiments would require very little mass, but could greatly advance our understanding of how Earth microorganisms can withstand the perils of the lunar environment,” Schuerger and his fellow researchers conclude.

Key finding

One of the key findings of the LMS model was that spacecraft hardware on the Moon were exposed to incredibly high biocidal conditions in which the outside surfaces were very likely sterilized during the first lunation on the Moon.

On-the-spot investigation – Earth’s Moon, lunar microbial survival? Credit: NASA

The biocidal and interactive effects of UV irradiation, high-temperatures, cis-lunar vacuum, and ionizing radiation would have induced as many as 23 “lethal doses” on all bacteria on spacecraft external surfaces during each and every lunar day –roughly 14.45 days, Schuerger concludes.

“Thus, over the course of 30, 40, and roughly 50 years, we should expect absolutely no microbial survivors on external surfaces. The only sites in which surviving bacteria ‘might’ persist would be on deep internal structures that are protected from all biocidal factors except the high-vacuum environment on the Moon,” Schuerger told Inside Outer Space.

For a copy of this paper — A Lunar Microbial Survival Model for Predicting the Forward Contamination of the Moon — go to:

https://www.liebertpub.com/doi/10.1089/ast.2018.1952

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