While our Moon is airless, research indicates the presence of hematite, a form of rust that normally requires oxygen and water. That has scientists puzzled.

PASADENA, Calif. (NASA PR) — Mars has long been known for its rust. Iron on its surface, combined with water and oxygen from the ancient past, give the Red Planet its hue. But scientists were recently surprised to find evidence that our airless Moon has rust on it as well.

A new paper in Science Advances reviews data from the Indian Space Research Organization’s Chandrayaan-1 orbiter, which  discovered water ice and mapped out a variety of minerals while surveying the Moon’s surface in 2008.