The Moon might be the closest celestial thing to Earth, but it's still pretty mysterious.
We all see it in the sky most nights, but few of us really know what's going on with it. If you'd like an example, just take this new information - the Moon is apparently shrinking.
That's right; because the Moon's interior is constantly, albeit very slowly, cooling down, the whole thing is gradually getting smaller as it contracts.
The Moon has been around for over 4.5 billion years, according to our best estimates, and in that time it has reportedly shrunk by around 100 meters in circumference.
Advert
That might not seem like loads, since you're therefore talking about microscopic changes each year, but in galactic terms it's still a meaningful process. The new findings are detailed in a study called Tectonics and Seismicity of the Lunar South Polar Region, published by the American Astronomical Society in The Planetary Science Journal.
For one thing, humanity is starting to gear up for what some are calling a second great era of Moon landings in the next decade, with space agencies such as NASA set to return astronauts to its surface for the first time in years.
The chosen landing sites that might have been perfect decades ago have subtly but importantly changed since then, and in some cases this is linked to the shrinkage.
It's been assumed in some scientific circles that the Moon's south pole might be ideal for eventual habitation, for example, but it's also been found to have fault lines that could be subject to moonquakes.
Advert
This is because the Moon's surface is steadily getting more brittle over time, leading to cracking and wrinkling.
A moonquake is a pretty different proposition to an earthquake, too - one can apparently last for hours rather than minutes or seconds, since there aren't tectonic plate divisions, oceans or continents to interrupt them.
According to lead author on the study, Dr Thomas R Watters from the National Air and Space Museum: "Our modelling suggests that shallow moonquakes capable of producing strong ground shaking in the south polar region are possible from slip events on existing faults or the formation of new thrust faults."
Advert
This doesn't spell the end of plans to build proper bases on the Moon, but it does add another major factor that agencies and missions need to consider before they go ahead.
The good news is that contingencies and careful planning are basically mandatory for any space mission, especially one involving human crew, so this information should hopefully just add to the chances of success.