Picture the plain at Tranquility Base right now. The lower half of the lunar module still stands where Neil Armstrong and Buzz Aldrin left it. Around it lies disturbed grey soil, discarded equipment and the paths the astronauts followed as they worked.
Individual bootprints are too small for an orbiting camera to resolve, so we cannot look down today and inspect the ribbed tread of Armstrong’s boots. What we can see are the broader trails created by many footsteps. NASA’s Lunar Reconnaissance Orbiter, which has been studying the Moon since 2009, has photographed the Apollo sites in enough detail to reveal the descent stages, equipment, rover tracks and darker lines of disturbed soil where astronauts walked.
More than half a century later, those marks remain clearly visible from orbit.
A world with almost no weather
The reason is simple: the Moon has no substantial atmosphere. Without one, it lacks nearly all the familiar forces that erase footprints on Earth. There is no wind to blow fresh dust across them, no rain to wash them flat, no flowing water, no frost breaking up the ground and no plants pushing through the soil. As NASA explains, the Moon does not experience weather like Earth’s wind, rain or snow.
NASA’s weather-on-the-Moon page puts it more vividly: “On the Moon, snow does not fall. Thunder never rolls.” There are enormous temperature changes between lunar day and night, but there is almost no air to carry heat, form clouds or drive weather across the surface.
The Moon is not a perfect vacuum, though. It possesses an extraordinarily thin exosphere: a scattering of atoms so sparse that they rarely collide with one another. A study of soil returned by the Apollo missions concluded that meteorite impacts produce at least 70 percent of this tenuous atmosphere by vaporising material from the lunar surface. A smaller share is produced when particles in the solar wind strike the ground and knock atoms loose.
That atmosphere is far too thin to create wind capable of sweeping away a footprint. But the impacts that help sustain it point to the process that will eventually erase the Apollo marks.
The impacts that slowly erase the surface
The Moon is constantly struck by material from space. Some objects excavate enormous craters. Far more are tiny particles travelling at tremendous speeds. Each impact disturbs a little soil, while debris thrown from the impact can land elsewhere and disturb still more.
Scientists call this continual mixing of the lunar soil impact gardening. It does not resemble erosion by wind or water. Instead, the surface is gradually punctured, overturned and covered by material thrown from impacts occurring nearby or far away.
The process is slow on a human timescale, but not motionless. In 2016, Emerson Speyerer and his colleagues compared thousands of before-and-after images taken by the Lunar Reconnaissance Orbiter. Along with newly formed impact craters, they found thousands of smaller surface changes created by ejecta from distant impacts.
From those observations, the researchers estimated that 99 percent of the Moon’s upper few centimetres of soil would be overturned on a timescale of about 81,000 years, more than one hundred times faster than earlier models had suggested.
That figure does not mean every footprint will vanish after exactly 81,000 years. Impact gardening is random and uneven. One print could receive a direct hit relatively soon, while another might avoid significant disturbance for much longer. Nor does overturning every part of the surface mean that every trace of disturbance immediately becomes undetectable.
What it does mean is that the fine details of an individual print cannot be assumed to remain crisp for millions of years. The narrow ridges left by a boot sole will gradually be broken, covered and mixed into the surrounding regolith. Broader paths made by repeated footsteps may remain detectable after individual tread patterns have blurred, while the metal landers and larger equipment should persist longer still.
Mark Robinson, the principal investigator for the Lunar Reconnaissance Orbiter Camera, once suggested that the tracks would disappear first as the soil was repeatedly mixed, followed eventually by the smaller equipment and then the landers themselves. He offered a deliberately broad estimate of perhaps ten to one hundred million years before no recognizable trace of Apollo remained. That was an informal estimate for the sites as a whole, not a precise lifespan for individual bootprints.
The Moon as an accidental archive
The stability of the lunar surface was already apparent during the Apollo programme.In 1970, Leonard D. Jaffe published a comparison in Science between photographs taken by Surveyor 3 in 1967 and photographs captured when the Apollo 12 astronauts visited the site 31 months later.
Jaffe examined areas that Surveyor’s landing pads and soil sampler had disturbed. The ridges created by the spacecraft were still standing, and areas darkened by fine material thrown up during its landing still appeared dark. Apart from changes caused by the visiting astronauts, the comparison found only one definite difference: a particle about two millimetres wide that appeared in a later photograph inside a Surveyor footpad imprint.
That does not mean nothing had happened. Changes smaller than the cameras could resolve may have occurred, and individual atoms and dust grains were continuously being moved by radiation and impacts. But at the scale visible in the photographs, the disturbed ground had remained remarkably stable for more than two and a half years.
On Earth, a footprint on a beach can disappear with the next tide or wind. A print in mud may survive until the next hard rain. Even a mark set in concrete lasts only as long as the pavement around it. Nearly everything people build enters a slow argument with water, weather and living organisms, and those forces usually win.
The Moon lacks most of those opponents, so evidence placed on its surface can endure for spans that dwarf a human lifetime. It is not an unchanging museum: impacts continually rewrite it, grain by grain and crater by crater. But compared with Earth, the rewriting happens with extraordinary patience.
The Apollo trails are therefore more than abandoned tracks. They are physical evidence, pressed into another world’s geology, that human beings once descended a ladder, crossed the lunar ground and returned home. Their sharpest details will not last forever, and no one can give an exact date when the final footprint will become unrecognizable. Yet the sites themselves may remain legible long after the machines that built the spacecraft, the cities that celebrated their return and probably many of the languages now used to tell their story have disappeared.
