The Moon may not have been as desolate as it is today – and could have supported life on its surface after its formation some four billion years ago.
This revelation comes just days after the anniversary of Neil Armstrong and Buzz Aldrin setting foot on the Moon, a first for humankind, on July 20, 1969.
A paper published in Astrobiology on Monday described two periods in the history of Earth's natural satellite, during which the conditions may have been ripe for life to develop. The first window of opportunity was shortly after it was forged from a gigantic impact between Theia, an early planet, and Earth 4.5 billion years ago, and the second window was around 3.5 billion years ago.
The debris disk from which the Moon formed would have retained some water and a small concentration of volatiles. After the accretion process, where the disk grows in mass, the Moon is expected to have been molten with flowing oceans of magma.
These oceans would have spewed out large volumes of hot gassy volatiles, including water vapour. Liquid pools of water and atmospheres could have formed during these fertile periods.
"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," said Dirk Schulze-Makuch, coauthor of the paper and a professor at Washington State University in the US.
There is evidence the Moon held on to some of that water. In previous studies, scientists have found hundreds of millions of metric tons of water ice on the Moon. There is also a more water concentrations of several hundred parts per million hidden inside its mantle.
The early Moon may also have been protected by a magnetic field to protect it from the relentless solar wind that stripped away any atmosphere. Although conditions may have been right for life to emerge, the researchers believe it’s more likely that it would have been brought there by a meteorite.
Fossilized cyanobacteria has been found in stromatolite – sedimentary rocks made out of layers of the bacteria stacked onto another – on Earth. The oldest samples are between 3.5 and 3.8 billion years old, during a tumultuous period in the Solar System where it was filled with giant meteorites flung to and fro between planets.
Meteorites could have picked up some of the cyanobacteria on Earth when smashing off its surface, and landed on the moon. Some of the bacteria could have survived the impact.
"It looks very much like the Moon was habitable at this time," Schulze-Makuch said. "There could have actually been microbes thriving in water pools on the Moon until the surface became dry and dead."
To collect evidence for their theory, the astroboffins will need rock deposits scraped from the lunar surface to see whether there are signs of water, and any other indication of other ingredients necessary for life. Scientists could also perform lab experiments to see whether cyanobacteria can survive in conditions that mirror the environment on the young Moon. ®