There may be a couple of hundred thousand miles between Earth and the moon, but our planet shares some striking geological similarities with our nearest neighbor in the sky. One of those similarities is the rock anorthosite.
The crystalline rock makes up much of the lunar highlands—it’s the lighter colored gray you can see when you look up at the moon—and its core mineral is the most common on the lunar surface. It’s thought to have formed during the initial cooling of the moon, as magma hardened into solid rock after its violent birth.
On Earth, you can also find anorthosite across several continents, though it’s less widespread than it is on the moon. The photo below shows one of the larger collections of the rock on Earth, the Saririaky massif in Madagascar, estimated to be almost 40 square miles in area.
This stunning image—revealing the pale anorthosite against the rock and soil around it—was snapped by an astronaut on board the International Space Station on August 28th. NASA doesn’t say which ISS crew member took the shot, though they note it was taken with a Nikon Z9 with a focal length of 400 millimeters.
The Saririaky massif is the largest of four anorthosite blocks in this part of southwestern Madagascar, with large-scale deformations of continental crust thought to be responsible for spreading the rock out to different regions. This particular massif is estimated to be at least 600 million years old, making it not quite as ancient as the 4-billion-year-old anorthosite on the moon.
While the composition of anorthosite can vary and doesn’t exactly match the mixtures on the moon, these outcrops on Earth are an invaluable way of studying what’s on the lunar surface without the need for any rockets, space suits, or moon buggies.
Scientists have previously identified anorthosite deposits in Montana as being particularly moon-like, which means the rock can be used as a close analog for the lunar equivalent. These rocks are older as well, around 2.7 billion years in age. “These simulants are extremely helpful when it comes to testing equipment, space suits, or anything else that will come in contact with the lunar surface when humans go back to the moon,” NASA lunar geoscientist Sarah Deitrick explained in a statement.
To that end, NASA wants to get humans back on the moon in 2028, and lunar-like rocks here on Earth will be a crucial part of the preparation. 
Enjoying Nautilus? Subscribe to our free newsletter.
Lead Image: NASA