screenshot filched from Dr Maggie’s presentation – the orientation of lobate scarps on the moon
Jacinta: So we’re trying to explore more about the mess that is the universe, or more accurately, the mess that’s our understanding of the universe, and, to maintain our bonobo bonafides…
Canto: I like that one.
Jacinta: … we’ll get our info solely from the female experts in the youtubeverse, such as Dr Sabine, Dr Becky and Dr Maggie, and any others we happen to come across.
Canto: So starting with our neighbourhood, I’d heard vaguely about the Artemis missions, something about the moon, but my attention was grabbed, I think by a recent Skeptics Guide podcast, or it might’ve been New Scientist, to the effect that we’re going back to the moon next year!
Jacinta: Yes, I think as part of a series, but next year’s crewed mission will be nowt but a flyby. Anyway, here’s some info from Wikipedia, which is already breaking my promise, unless the article was written by a woman. Anyway the overall programme is called Artemis 2 and this first flyby mission will launch in September next year at the earliest. Four astronauts, one of them a woman, Christina Koch. Slowly getting there. And humans on or near the moon for the first time in 53 years! Or more. Fact is, there have been many delays and changes of plans, so we shouldn’t hold our breath.
Canto: Anyway, let’s focus for now on the moon itself. We know it’s slowly spiralling away from us, and wrote about it years ago. The rate is 3.8 cm a year, a figure we can measure because of devices left on the surface all those years ago by one of the Apollo missions. Don’t know if it’s spiralling away faster – I mean if the distance is increasing – you know, next year it’ll be 3.81 cms further away than this year, and so on…
Jacinta: It makes sense, because as it spirals away, it’s moving that tiny bit from Earth’s centre of gravity – the pull would be ever so slightly less strong… am I right? But then, as that happens, the moon would travel around earth more slowly, just as the outer planets travel more slowly around the sun.
Canto: I think that’s right, but both bodies will probably be destroyed by the sun by the time the moon says goodbye.
Jacinta: Anyway we’ll talk more about Artemis 2 as time goes by, now some things we’ve learned from Dr Maggie Lieu – first that the moon is rusting, which is something of a mystery, since there’s no oxygen there and very little water, the two principal components creating rust – generally iron oxide – on Earth.
Canto: Yes they’ve confirmed the presence of hematite, a type of iron oxide, at the poles in particular, where most of the moon’s water (ice) is. They’ve also found more of it on the side facing Earth, and have proposed that it actually derives from Earth, via our magnetic field:
In 2007, Japan’s Kaguya orbiter discovered that oxygen from Earth’s upper atmosphere can hitch a ride on this trailing magnetotail, as it’s officially known, traveling the 239,000 miles (385,00 kilometers) to the Moon.
Jacinta: Okay enough about rust. So the moon is generally a lot cooler than Earth due its lack of an atmospheric blanket. It’s been cooling ever since it left Earth. Which also means it’s shrinking, as the liquid outer core has solidified, decreasing in volume?
Canto: Yes and that shrinking leads to a wrinkling and breaking up on the moon’s surface, due to thrust faults, with one section of the moon’s crust thrusting over another, something like tectonic plates, but without the tectonic plates. It results in what the cognoscenti call lobate scarps – something to do with the way they look (check them out on Google images, but they’re still not clear to me). Anyway, lots of them in one area tells us that something’s happening beneath the surface. Such stresses can result in moonquakes, measuring up to 5 on the logarithmic Richter scale.
Jacinta: Measuring devices left on the moon during the Apollo missions have connected moonquakes with areas covered in lobate scarps, of which thousands have been discovered. But it’s not really like tectonic plates, with seismic activity occurring at tectonic boundaries – it’s seemingly a much more random sprinkling of these scarps and thrust faults. Remember, huge mountain ranges like the Himalayas and the Andes have been produced by the bashing together of tectonic plates, but there are no mountain ranges as such on the moon.
Canto: The Lunar Reconnaissance Orbiter Camera (LROC) has mapped these lobate scarps and found a striking pattern in their orientations.
Jacinta: Yes, let’s quote Dr Maggie on this:
These [lobate scarps] cover the entire surface of the moon, but when you take a look at their orientations, as indicated on this map [see above] by the black arrows, you’ll notice something interesting. If these faults are caused by the moon shrinking, it should be shrinking the same in all directions, so you would expect these scarps to be in the same direction, but no, at the poles the scarps tend to be oriented perpendicular to the scarps at the equator. It seems that, in addition to the moon’s shrinking, the Earth’s gravitational pull is affecting these scarp lines.
Canto: So enough quoting – how do they come to this conclusion?
Jacinta: Well we know that our tides are affected, or created, by the moon’s gravitational pull, so you’d expect the Earth’s gravitational effects on our moon to be far greater, though of course they can’t be tidal effects, although they’re described as tidal forces, which is a bit confusing. As Dr Maggie reports, our gravity creates moonquakes, of a different type to the shallow moonquakes caused by the moon’s shrinkage. These shallow quakes originate a few kilometres below the surface, and occur at a rate of about 7,000 a year, but tidal forces create deep moonquakes, originating hundreds of kilometres below the surface, at a rate of tens of thousands a year. And they’re not the only moonquakes – meteor impacts can cause them as well as the day-night cycle, which causes freezing and thawing of the surface.
Canto: So yes, the moon is shrinking, very very slowly. Not a big bother, though those moonquakes might be, for the Artemis missions. Presumably they’re not predictable. And I suppose that map they’re making of all those scarpy things might help them to choose a safer landing spot, if they’re going to land women on the moon in the future.
Jacinta: Nice one. Something to explore in future posts – what NASA’s actual plans are for Artemis 2. A human colony or just a bit more surface-scraping…
References
https://en.wikipedia.org/wiki/Artemis_2