Unexplained Craters On The Moon | Unveiled

Unexplained Craters Found on the Moon

As the closest astronomical object to Earth, the Moon is one of the few celestial bodies that’s visible with the naked eye. It has enthralled humankind for as long as we’ve been a cognitive species. And yet, despite thousands of years of observation, we’re far from uncovering all its secrets.

This is Unveiled, and today we're exploring three extraordinary, unexplained craters found on the Moon.

Formed out of a collection of space debris most likely created by a collision between Earth and a protoplanet some 4.5 billion years ago, the Moon (like the Earth) has been subject to a bombardment of asteroid and meteorite crashes throughout its lifetime. Unlike the Earth, however - which has processes such as erosion, plate tectonics, and volcanism to continually refresh itself - the Moon has no way of repairing its many collision sites. It’s effectively frozen in time, and the craters we see on its face today are the remnants of a tumultuous past dating back billions of years.

There are parts of that past that we can chart with confidence, but others that we’re still not sure about. Throughout human history, the Moon has been observed as a method of keeping time, worshipped as a deity across numerous civilizations, and even seen as a source of prophecy. But still, even after millennia of human analyses, centuries of astronomical observations, and six crewed lunar landings, there are some ultra-mysterious craters, etched deep into the surface, that we still can’t explain.

The first is the South-Pole Aitken Basin, which is the oldest and largest crater on the Moon, and one of the largest known craters in the solar system. Being approximately 1,500 miles wide and 5 miles deep, it stretches far across the lunar surface… and, broadly speaking, we do know how it got there. It’s the product of a massive asteroid collision around 4 billion years ago. But, because the South-Pole Aitken Basin is located on the far side of the Moon, it’s only been observable to us since the earliest probes were sent that way in the early 1960s. For most humans who aren’t trained astronomers, it’s totally hidden from Earth… although it continues to throw up mysteries for science to unpick. Such as in 2019, when a sizeable, unexplained mass was detected beneath it.

Peter B. James is a professor of planetary science and geophysics at Baylor University, in the US. In his study, “Deep Structure of the Lunar South Pole-Aitken Basin”, he analysed data from two key NASA moon missions - including the Lunar Reconnaissance Orbiter - to reveal a massive, seemingly metal mass, reportedly five times the size of Hawaii… and apparently suspended in the lunar mantle beneath the crater.

While scientists are unsure what the mysterious mass is, there are two main theories about its origins and structure. The first is based on the Lunar Magma Ocean Solidification theory, which says that the early Moon was once host to fiery seas of magma… that have since dried up, leaving only their remnants on the face of the moon in the form of the dark spots that we can see from Earth today. As for the mass detected by Peter James, it’s suggested that it is also an immense collection of dense oxides, deposited at the same moment in lunar history, during the cooling process of the magma oceans.

It’s a strong theory, but the prevailing theory at present suggests something else; that the South-Pole Aitken Basin mass is actually a leftover material from the asteroid that caused it to form in the first place. An ancient asteroid, its iron-nickel core has somehow been prevented from sinking into the Moon's inner core, and so it has been eerily preserved, suspended in the lunar mantle for all this time.

Not every crater is afforded such longevity, however, as shown by today’s second example. In 1824, the German astronomer and cartographer Wilhelm Lohrmann published a series of lunar maps, appropriately titled; "Topography of the Visible Surface of the Moon”. While these maps are still today celebrated for their accuracy, there’s one crater depicted in them that has triggered controversy ever since.

When observing one of the Moon's youngest craters, located in the Sea of Serenity, Lohrmann noted that what he called the Linné Crater was about 5 miles across. This description was then supported by Lohrmann’s fellow astronomers, Wilhelm Beer and Johann Mädler, who published their own maps thirteen years later, in 1837. And so, the Linné Crater remained unchanged for a further three decades, until a fresh series of observations carried out in 1866, by one Johann Friedrich Julius Schmidt.

Like his contemporaries, Schmidt had previously drawn many maps of the Linné Crater, always finding it the same (or extremely similar) to Lohrmann’s original. When he re-observed it in 1866, though, he noticed that the hole was gone. In the place where it should have been there was now a simple white patch, with a small mountain in the centre… that had seemingly shot up in less than thirty years. Schmidt’s discovery caused interest in the disappearing crater to skyrocket.

There followed a series of investigations by the top astronomers of the time, and it was a Father Angelo Secchi of Rome who ultimately realised that the “mountain” noted by Schmidt was actually a tiny crater itself, about one-and-a-half miles across - and much smaller than Lohrmann’s original. So now, while science had shown that the Linné Crater hadn't disappeared, it was widely agreed that it had shrunk. So, what had caused such a sudden change?

At the time, it was generally believed that it was a result of lunar volcanism… although modern astronomers tend to reject this theory, despite there still being precious few alternatives out there. The leading counter theory is that the differing observations - between Lohrmann in 1824 and Schmidt in 1866 - were simply due to the telescope limitations that both were working with. The argument against that, however, is that the Linné Crater is easily distinguished, without any other landmarks nearby to distract from it. It seems unlikely, then, that so many experienced and esteemed astronomers would have continually made the same mistakes. And so, the true nature of the Linné Crater's metamorphosis remains a mystery.

Finally, we’re heading to the north-western region of the near side of the Moon, and to the 25-mile-wide Aristarchus Crater, famous amongst moon watchers as being the brightest spot on the lunar surface. It’s also considered one of the most geologically complex regions of the moon, and it’s known for emitting a high concentration of generally baffling light activity.

Over the centuries, astronomers have witnessed hundreds of unexplained, sporadic flashes of light across the moon. They’re collectively known as Transient Lunar Phenomena, but the Aristarchus Crater is where so many of them appear to originate. The first documented sightings date back to the 1500s… but it wasn't until 1650 that the Polish astronomer Johannes Hevelius could use the still relatively new invention of the telescope to more accurately observe where the illuminance was coming from. And, since then, it’s been all eyes on Aristarchus.

Significantly, Hevelius also noted that the region inside the crater appeared mountainous. Then, when Britain’s William Herschel observed lights omitting from the same crater and mountains more than a century later, in the 1700s, he concluded that what Hevelius had truly observed were volcanoes… suggesting that the flashing lights of Aristarchus doubled up as a display of lunar volcanism. But, again, the claims of volcanic activity on the lunar surface are widely unsupported by modern science. Today we know that, while there are volcanoes present on the Moon, they’ve been dormant for millions of years.

As a result, the Transient Lunar Phenomena omitting from Aristarchus is something which continues to baffle scientists. Perhaps the closest we came to discovering the true source of these glowing lights came back in July of 1969, when the Apollo 11 astronaut Neil Armstrong also noted an odd luminescence coming from the crater. Unfortunately, he had… other plans… and couldn’t make an unscheduled landing on his way to Tranquillity Base. All of which means that the mystery remains unexplained.

For many, we may never reveal the true nature of these particular lunar features until we do visit them in person. What’s really hiding beneath the South Pole-Aitken Basin? What’s really happening with the Linne Crater’s changing size? And why on Earth are there flashing lights coming from Aristarchus? Ultimately, the answers are not of this Earth… but they are looking down on us. And those are three unexplained craters found on the moon.