Why Is The Moon Turning Red? | Unveiled

Why is the Moon Turning Red?

If there’s one thing we can rely on, it’s that the moon will always be there. Night after night. But our long-serving lunar satellite is actually changing, and in stranger ways than we could have ever imagined.

This is Unveiled, and today we’re answering the extraordinary question; why is the moon turning red?

The Moon Mineralogy Mapper is a device designed by NASA’s Jet Propulsion Laboratory to study the composition of the moon. It’s what’s known as a spectrometer, which is a machine that produces spectral maps; which are maps that show the exact chemical arrangement of any given planet or, in this case, satellite. The Moon Mapper works because every element on the moon emits a different wavelength of light on the electromagnetic spectrum, so it meticulously records these to provide us with some of the most detailed images we’ve ever seen. It was this same mapper, in fact, that first detected water on the moon in 2009.

In 2020, scientists re-examined some past data from the Moon Minerology Mapper; data that was originally gathered as part of a survey taken twelve years earlier… back when the mapper had been installed on Chandrayaan-1, an Indian spacecraft. Upon looking again, the scientists - from the University of Hawaii - discovered something previously thought to be completely impossible. Analysing the lunar poles in particular, they appeared to be going rusty. Specifically, the mapper identified hematite, an iron oxide produced when iron meets water and oxygen, leaving rust. The problem here is that the moon shouldn’t have enough water or oxygen for rust to form, so how did it get there?

Well, it most likely has a lot to do with our planet, Earth. The most straightforward theory is that for at least 2.5 billion years, Earth’s plants have been pumping out oxygen, and the moon has picked up some of that. We can find proof of this in certain isotopes of oxygen that have now been found on the moon… because they’re isotopes that originate from Earth. The leading idea is that when the moon passes through Earth’s magnetotail, which is the trail the planet leaves behind as it orbits the sun, it’s then subjected to at least a little bit of our world’s oxygen. This happens only for short periods, but regularly. Although it still doesn’t completely solve the mystery.

Because, what about the water? While we know that the moon does have ice, the rusty hematite found by the mapper was not close enough to these deposits. The best theory for where the required water comes from, then, is space dust… the idea being that this dust has in some way reacted with the lunar surface over billions of years, to form traces of water. This, combined with the oxygen inherited from Earth, is what has created the conditions necessary for the moon’s iron to oxidize – for the rust to form. We’re still a long way from being able to see the effects of this with the naked eye, however. If you go out and look up at the moon tonight, you’re not about to notice big red splodges at the top and bottom of it… because, without the Minerology Mapper, we’d really have no idea that this was happening. In fact, it’s thought that the rust is only able to form for a few days each month… it’s just that those days have now added up over billions of years to cause this interesting phenomenon.

This is by no means the first time that we’ve seen this happen in the solar system, though. It’s also iron oxide that gives Mars its distinctive colour, putting the “Red” into the Red Planet. So, if the moon developing hematite is an inevitable process thanks to Earth’s abundant plant life and the huge amounts of oxygen our planet produces, then, one day, the lunar surface could even look a bit like Mars does now. And, unlike so many other long-term ecological or atmospheric changes, this is something which should happen regardless of what humans do. Even if Earth’s environment is severely damaged by human activity, and even if we eventually go extinct… it’s thought that, given enough time, the Earth will recover. And it will continue producing oxygen all the while, so its magnetotail will remain, and the Moon will still slowly be fed all that it needs to gradually rust. Sure, if the current predictions play out, it will take a long time (like, billions more years!) but it’s thought that not even Mars was always red. Its colour is iconic now, but it’s believed that our planetary neighbour once had a gray-ish, charcoal look, a long time ago.

All of which means that we shouldn’t be too worried about the moon going rusty, even if it does initially sound like it might be a bad thing. The creation of iron oxide is a natural process, and what we’re discovering now doesn’t mean that the moon is in some way being damaged. It isn’t going to fall apart or collapse or rust away into nothingness. It’s not like an old bicycle that’s been left out in the rain, or a rusty hinge that no longer works, it’s just evidence of the moon evolving along with the rest of the solar system. And, regardless, the amount of iron oxide present today is still so negligible that we need a spectrometer to see it at all… by the time it becomes significant enough to see from Earth, who knows what other changes our planet will’ve also gone through!

But if you think a red moon is more interesting than it is scary or worrying, there’s good news: because, technically, you won’t have to wait hundreds of millions of years to see one. In fact, red moons are a fairly regular occurrence on the calendar… just not in the same way. During a lunar eclipse, a phenomenon called Rayleigh scattering - a type of scattering of light - means that the moon appears red in the sky, in what’s also known as a “blood moon”. Rayleigh scattering and blood moons have zero to do with iron oxide and rust, though, and are all to do with how light reaches our eyes… with Rayleigh scattering also being the reason why the sky often appears vividly red, especially at dawn and dusk.

Culturally-speaking, blood moons are believed by some to be harbingers of doom, but really, physically-speaking,they’re completely harmless - they only indicate a lunar eclipse. Blood moons can also coincide with other lunar events, too, like supermoons… with a supermoon being when a full moon happens precisely when the moon is at its perigee (i.e., when it’s the closest it gets to Earth - which is roughly 221,500 miles away). When the moon is at its apogee and is furthest away, this can be called a “micro moon”. So, technically, we could also experience a “blood micro moon”, if all those things aligned.

The harvest moon is another of note, described as the full moon closest to the autumnal equinox - the date in fall when night and day are the same lengths. We call it a harvest moon because, traditionally, farmworkers could continue to reap that year’s harvest long into the night because the light of this particular moon is so bright. Lots of full moons have nicknames like this, though, including the hunter’s moon (which is directly after the harvest moon) and the wolf moon (which is the full moon in January). In 2019, the world was treated to an incredibly rare “super blood wolf moon”, a full moon happening in January during a total lunar eclipse when the moon was at its perigee.

Similarly, a blue moon is a lunar phenomenon that doesn’t really denote any change in colour, despite the name. Most of the time, a blue moon is simply the second full moon in a month, which happens from time to time because the lunar cycle is only around twenty-eight days long, making it shorter than the length of a calendar month. It’s where the saying “once in a blue moon” comes from, because it’s quite rare.

But the moon can also appear physically blue to us here on Earth, as well, although this is to do with Earth’s own environment rather than the lunar cycle. Whenever there are large amounts of debris in the atmosphere, it can tint the sky different colours, like after volcanic eruptions and forest fires. And, that colour can sometimes be blue. After the 1883 eruption of Krakatoa, one of history’s most famous eruptions, for example, it was reported that the moon looked blue because there was so much ash in the sky. We also have reports of a blue moon after the eruption of Mount St. Helens in 1980. And finally, the human eye does sometimes perceive standard moonlight as blue, even though it definitely isn’t. This is because of the Purkinje effect, which relates to how human eyes are better at seeing blues and greens in low light conditions – like, at night – as opposed to reds and yellows.

All to say, however, that it’s no bad thing that the moon is slowly rusting, even if Earth is ultimately to blame, because it’s happening due to completely ordinary – if incredibly rare – astronomical circumstances. There are also other explanations as to why the moon might appear a different colour to us when we look at it, but that’s why the moon is turning red.