The Moon may have been habitable for life during two separate periods in its ancient past, according to a study led by Dirk Schulze-Makuch of Washington State University (WSU).
Based on analyses of lunar rocks and data returned by various space missions, Schulze-Makuch’s research team believes the Moon may contain more water ice than scientists suspect, including possible water ice beneath its surface.
While the Moon is currently dusty and lifeless, it may have been habitable for two windows in the past, one four billion years ago, and the other 3.5 billion years ago, the researchers propose.
As it was forming four billion years ago, the Moon released massive amounts of volatile gases, including water vapor. Three-and-a-half billion years ago, the Moon was volcanically active.
Under both of these conditions, the volatile gases could have created a thick atmosphere that endured for several million years as well as pools of liquid water on the lunar surface.
The researchers theorize the ancient Moon also had a magnetic field that would have shielded any life present from solar radiation.
“There could have actually been microbes thriving in water pools on the Moon until the surface became dry and dead,” Schulze-Makuch said.
Today, the Moon has a very weak magnetic field and a very thin atmosphere composed of gases such as sodium and potassium.
Earth’s earliest life, cyanobacteria began sometime between 3.5 and 3.8 billion years ago. The ingredients needed by these single-celled organisms, which generate oxygen through photosynthesis, as well water and the organisms themselves, could have been brought to the Moon, as they were brought to the Earth, by meteorites.
Meteorite impacts were common in the violent early years of the solar system. It is possible that cyanobacteria-containing meteorites thrown off Earth’s surface during impacts could have delivered these microbes to the Moon.
“If liquid water and a significant atmosphere were present on the early Moon for long periods of time, we think the lunar surface would have been at least transiently habitable,” Schulze-Makuch stated.
Future searches for signs of ancient microbial life on the Moon could focus on obtaining samples from the areas known to have had the most volcanic activity 3.5 billion years ago, with the aim of finding water and/or fossils.
A paper on the researchers’ findings has been published in the journal Astrobiology.