Leonard David's INSIDE OUTER SPACE

European Large Logistic Lander enables a series of proposed ESA missions to the Moon that could be configured for different operations such as cargo delivery, returning samples from the Moon or prospecting resources found on the Moon.
Credit: ESA/ATG-Medialab

New research shows that exhaust from lunar landers can rapidly spread around the Moon and potentially contaminate scientifically vital ices at the lunar poles.

Native ices sequestered in the Moon’s poleward craters — ices that may date back several billion years — will need to be carefully considered during increased efforts to return humans to the Moon.

Image showing the distribution of surface ices (depicted as blue dots) at the Moon’s south pole (left) and north pole (right), detected by NASA’s Moon Mineralogy Mapper instrument. The grayscale in this image depicts temperature, with darker being colder, showing the ices are concentrated in the darkest and coldest locations, the crater shadows.
Credit: NASA

Study results have been led by scientists at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, published in the Journal of Geophysical Research: Planets.

Origin of water

Parvathy Prem, a researcher at APL and the lead author on the study, explains that there are few places where researchers can find traces of the origin of water in the inner solar system.

Reading that record requires measuring the composition of those ices as well as their various isotopes to deduce where they likely came from and how they may have gotten there.

Frozen-out exhaust gases from robotic or human exploration that collect on those ices, Prem adds, could confound those measurements, even if the lander touches down hundreds of miles away.

Global impact

“The interesting thing about Parvathy’s work is that it shows very well that the effect, while small and temporary, is global,” said Dana Hurley, a planetary scientist at APL and coauthor on the study, in an APL statement.

An artist’s concept from 1969 depicts a lunar module descending to the Moon’s surface. Because of the Moon’s very thin atmosphere, the exhaust expands significantly and can remain in the atmosphere for months.
Credit: NASA/Johnson Space Center

Computer simulations of water vapor emitted by a 2,650-pound (1,200-kilogram) lander — about a quarter of the dry mass of the Apollo lunar module — touching down near the Moon’s south pole showed exhaust takes only a few hours to disperse around the entire Moon. From 30% to 40% of the vapor persisted in the lunar atmosphere and surface two months later, and roughly 20% would ultimately freeze out near the poles a few months after that.

Sprawling Moon base supported by SpaceX Starships.
Credit: SpaceX

If the Moon landing spacecraft is heavier, or lands closer to the poles, its influence on the lunar surface and atmosphere may be more significant.

Fate of exhaust gases

Follow-up work should include measuring the amount of exhaust that’s around the Moon during and after future landings, Prem said, which would help narrow in on an answer to how much these exhaust gases “stick” to the surface. “But I would also suggest that modeling and monitoring the fate of exhaust gases should be a routine part of lunar mission development and planning.”

“Whether we intend to or not, we’re going to do this experiment of bringing exhaust gases with us,” Prem said.

It’s now a matter of deciding how we deal with them.

The paper — The Evolution of a Spacecraft‐Generated Lunar Exosphere – is available here at:

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JE006464

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