Waiting for Artemis ...
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Apparently, human-kind is on it's way to Mars, or at least, that's the new message that NASA (and a billionaire or two) is pumping up in the media. The mission referred to by NASA communications is called Artemis : named for the twin sister of the Greek god Apollo. Just in case you didn't get the point, that's a reference to the Apollo Program of the 1960s when NASA put MEN on the Moon ... and that today we are trying to be more inclusive (thank goodness !).
Put simply, the idea behind Artemis is to build a permanent logistical and science platform located at the South Pole of the Moon from which to springboard a Program to get humans to Mars ... and back.Why go to the Moon before going to Mars ? Because gravity is only 1/6th that of the Earth ... and so lifting materials into space is easier. Why the South Pole ? Because water ice has been identified in permanently shadowed craters and because you have a 360 degree horizon for scientific observations and measurements of the Solar System.
While NASA and its potential astronauts are pumped about Artemis, it's not going to be plain sailing. There are major uncertainties that have already cropped up. I'll mention just two here.
#1 : the funding. NASA is over-budget - which is a polite way of saying that it's broke, or very soon will be. Although part of the issue stems from the time and cost over-runs of the Webb Space Telescope, this applies especially to NASA's Solar System exploration program. You are probably aware that the joint NASA-ESA Mars sample-return mission is currently being reconsidered, even though most of the samples have already been drilled and deposited om Mars by the Perseverance rover ready for pick-up by a second rover that will cost a further unbudgeted $10B US that neither agency can afford. Perhaps you have also heard of NASA's VERITAS mission to place an orbiting platform around Venus to remap the planet's surface during the coming decade. Well it hasn't exactly been cancelled (budget problems again), but last year it was put on "HOLD", though it appears to be back "ON" again this year. Don't hold your breath on that one !
#1 : the funding. NASA is over-budget - which is a polite way of saying that it's broke, or very soon will be. Although part of the issue stems from the time and cost over-runs of the Webb Space Telescope, this applies especially to NASA's Solar System exploration program. You are probably aware that the joint NASA-ESA Mars sample-return mission is currently being reconsidered, even though most of the samples have already been drilled and deposited om Mars by the Perseverance rover ready for pick-up by a second rover that will cost a further unbudgeted $10B US that neither agency can afford. Perhaps you have also heard of NASA's VERITAS mission to place an orbiting platform around Venus to remap the planet's surface during the coming decade. Well it hasn't exactly been cancelled (budget problems again), but last year it was put on "HOLD", though it appears to be back "ON" again this year. Don't hold your breath on that one !
#2 : the lunar water. I'm sure you all know that the Moon is a dusty place. We've known this since Apollo. We've also known for 60 years that the lunar dust is very abrasive. It's not surprising. 4.5 Ga of asteroid and meteor bombardment have ground the lunar rocks to a very fine powder. Those rocks are made of silicate minerals so the dust is essentially made of tiny nano-shards of the mineral plagioclase feldspar that slice and dice anything that they come into contact with, including spacesuits, but more especially the gaskets (rubber or silicone) on water purification devices. This means that not only could there be an issue with purifying the large quantities of water necessary for drinking, it's not even clear how to get all the dust out of the water ... which potentially poses major issues if you want to use it as rocket fuel (there are gaskets in rockets too !!)
In the mean time, while NASA tries to sort itself out, there are individual scientists who are getting on with their allotted task of studying the Moon and informing us of their results.
In the mean time, while NASA tries to sort itself out, there are individual scientists who are getting on with their allotted task of studying the Moon and informing us of their results.
There's a lot of scientific endeavour actively underway in the field of lunar science. To be sure, some of it is driven by the prospect of the Artemis program. The potential for funding is always a draw ... and why not ? What's remarkable however - and this is my personal view - is how much of the lunar science being undertaken today harks back to questions that were first asked years ago. Some of the science is a bit esoteric for a general audience, so - again, in my personal view - I have selected a short-list of topics that catch my geological eye, and that I think would be of interest to amateur astronomers such as ourselves. So let's start with that age-old question (pun intended) : Just how old is the Moon and how do we know ?
Yes, we are still asking this question in 2024 ... and there's a reason for it : Contradictions ! It turns out that when you look at the history of planetary orbits at the scale of the Solar System you arrive at a different age for the Moon than when you study the surface of the Moon itself ! How does this work ? The consensus on Moon formation is that it occurred by the collision of a Mars-size planet (Theia) with the proto-Earth at ~4.5 Ga. This means that Theia's orbit was unstable : most probably because of the migration antics of Jupiter - initially toward then away from the Sun - sometime during the first 100 My of Solar System existence. In this scenario the Moon first formed with a magma ocean some 100s km deep (maybe >1000 km - maybe the entire Moon was molten) that would have crystallised to solid rock within ~10 My of the collision. However, when Moon rocks collected from the surface by the Apollo Program were analysed (U/Pb in zircon crystals), the magma ocean appears to have solidified ~210 My after Solar System formation started. That would mean that if a magma ocean crystallises in only ~10 My, the collision must have occurred at ~200 My instead of <100 My ... and that's a big discrepancy. Well, in early 2024 planetary scientists published a solution to this apparent paradox. After confirming that the Moon did indeed form at ~50 My, they described a way to prolong the life of the magma ocean on the Moon. Yes, the lunar magma ocean cooled and crystallised ~10 My after the impact at ~50 My, but it heated up again, remelted and cooled all over again by ~200 My. How ? The initial orbit of the new-born Moon was likely highly elliptical, as opposed to nearly circular, which means that Earth's gravity affected the Moon differently in different parts of the Moon's orbit. This put a periodic squeeze / relaxation on the Moon that generated energy that turned into heat, and hence a new lunar magma ocean formed. Assuming that it took ~150 My for the lunar orbit to circularise, this would explain all of the available evidence, and solve the apparent paradox (50 + 150 = 200).
Neat !! However, this is really a confirmation (which is great in itself !!) of a story that I had already told you about two years ago, as you can see from this slide from my 2022 RASC talk.
https://www.simonhanmer52.ca/solar-system-science-202122.html
https://www.simonhanmer52.ca/solar-system-science-202122.html
In 2024, a headline read something along the lines of "The Moon turned itself inside out". Well ... I just had to read this one !! We've know ever since Apollo that there are Ti-rich lavas (rich in the dense/heavy mineral ilmenite) that we can detect on the lunar near-side. Note the blue in the middle image of the Moon in this slide taken directly from the 2024 paper. On the right-hand side is a representation of certain aspects of the lunar gravity field. We don't need to get into technical detail here, but you can see what look like blue "veins" all over the place, that are covered by (i.e.older than) the lunar Mare.
The story here is fascinating. These "veins" appear to be ilmenite-rich rock that forms thick, vertical sheets (mega-"dikes") within the lunar mantle beneath the lunar crust. The ilmenite is thought to be the dregs left-over from the crystallisation of the lunar magma ocean - that we just discussed - so they date from the first ~200 My of Solar System history, as we've just seen.
Because ilmenite-rich rocks are dense, the idea is that they would have sunk through the much less dense anorthosite crust ... apparently sinking - at least in part - as "vein"-like mega-dikes and ponding at depth within the lunar mantle.
Because ilmenite-rich rocks are dense, the idea is that they would have sunk through the much less dense anorthosite crust ... apparently sinking - at least in part - as "vein"-like mega-dikes and ponding at depth within the lunar mantle.
OK, but why are the ilmenite-rich lavas we see today concentrated on the lunar near-side ? Surely, the ilmenite-rich mega-dykes formed all over the Moon. Well, there's the very old, absolutely gigantic South Pole Aitken impact basin on the lunar far-side that some suggest really messed with the mantle of the early Moon, forcing the ilmenite-rich mantle to migrate to the antipode on the lunar near-side, just below what would eventually become the Mare Procellarum. The lavas that formed Procellarum would have been derived by the melting of the ilmenite-rich mantle directly below. So, ilmenite formed in the magma ocean that gave us the anorthosite crust of the Moon, sank into the underlying mantle, was gathered and concentrated on the near-side just below the lunar crust by a giant impact on the far-side of the Moon, then erupted onto the surface as the Mare Procellarum lavas.
In short ... I guess you could say that the Moon turned inside out !!!
In short ... I guess you could say that the Moon turned inside out !!!
It's an exciting and dynamic story ...
However ... this is really another confirmation (which again is great in itself !!) of a story that I had already told you about eleven years ago ... as you can see from this slide from my 2013 RASC talk.
https://www.simonhanmer52.ca/grail.html
This time the "confirmation" in 2024 comes from recent numerical modelling of how dense material (ilmenite) would sink as vertical sheets into the newly forming Moon , which is more a reflection of the increasing power of computers today than of new observations or data.
However ... this is really another confirmation (which again is great in itself !!) of a story that I had already told you about eleven years ago ... as you can see from this slide from my 2013 RASC talk.
https://www.simonhanmer52.ca/grail.html
This time the "confirmation" in 2024 comes from recent numerical modelling of how dense material (ilmenite) would sink as vertical sheets into the newly forming Moon , which is more a reflection of the increasing power of computers today than of new observations or data.
Another lunar story that keeps coming back is based on the idea that - 4.5 Ga after its formation - the Moon is still cooling and globally shrinking. I had trouble with this idea back in 2011 when I first talked to you about it. The idea is that if the Moon is still cooling, and therefore shrinking, then faults (fractures) and folds must be accommodating the shrinkage of the lunar surface. Studies since 2010 have been seeking to identify these faults and folds and attempting to link some of them to seismic shocks (moonquakes) that were recorded by the Apollo Program instruments left on the Moon. How do they do this ? They look for recent impact craters that have been partially obscured by material associated with a scarp (cliff or steep slope, then they attribute the partial covering of the impact crater to a shallow-dipping fault. It's not that I have an issue with the idea of cooling and shrinking, though it does seems to be a bit of a stretch (pun intended !) after 4.5 Gy. It's more that I have trouble accepting the observational evidence for the proposed faults and folds supposedly operating today on the Moon.
This is a slide from my 2011 RASC talk on the very same subject.
https://www.simonhanmer52.ca/shrinking-moon.html
On the left you can see how contraction (perhaps driven by global lunar shrinkage, but not necessarily) can generate a shallow-dipping fault and a topographic hill or scarp. However, on the right, you can produce the same scarp by sliding material down a pre-existing slope of unspecified age (maybe ~older or >>older) in what you would call a landslide. Both scenarios can result in the same features, but the one on the right does not require shortening of the lunar surface - or contraction of the Moon. Nor does it require that the slope down which material flowed has to be young !
So take another look at this image from the 2024 paper,and decide for yourselves which of the two scenarios might best apply.
BTW : Why publish this particular paper now in 2024 ? Because the structures evaluated are within the area of the Artemis Program planned for the lunar South Pole, and numerical modelling suggests that if there really are active faults in the area they could generate "landslides"... and Artemis might well be interested in some insurance. Great way of asking for more funding !
BTW : Why publish this particular paper now in 2024 ? Because the structures evaluated are within the area of the Artemis Program planned for the lunar South Pole, and numerical modelling suggests that if there really are active faults in the area they could generate "landslides"... and Artemis might well be interested in some insurance. Great way of asking for more funding !
The next story from 2024 is an as yet unresolved Sherlock Holmes mystery concerning a tiny feature ~3 km across with major potential repercussions for how we understand the thermal history of the Moon. As you probably know, on Mercury, Mars and the Moon, we can date how old a surface is by the density of impact craters that we find there. It's a bit rough around the edges, but it seems to pan out pretty well. Among the rocky inner planets, however, Earth and Venus do not fit this pattern. That's because lots of craters on Earth have been erased by erosion and plate tectonic crustal recycling, and covered on Venus by major, global, volcanic resurfacing during the past 1 Gy.
The feature shown here from two different angles is called Ina, located to the SE of the Imbrium impact basin (see red dot at upper right). If you think it looks "frothy", you would not be alone. However, it's actually made of low relief mounds (20m) sitting on a floor of rubbly volcanic rocks.
The feature shown here from two different angles is called Ina, located to the SE of the Imbrium impact basin (see red dot at upper right). If you think it looks "frothy", you would not be alone. However, it's actually made of low relief mounds (20m) sitting on a floor of rubbly volcanic rocks.
Ina has been known and puzzled over since the Apollo 15 mission. The issue is that Ina is a small lava pond - now cooled and crystallised of course - sitting on the top of a volcano. Although there are some very small impact craters, if you take the impact cratering statistics for Ina at face value, Ina would be <<100 Ma old, maybe as young as 33 Ma. However, the volcano it sits on top of is estimated to be ~3.5 Ga. That's one major discrepancy and a huge paradox attached to such a tiny feature. The paradox is that if Ina is really as young as the observable impact craters suggest, then how could the old, cold Moon have been warm enough to produce even this small amount of lava. Potentially, one might have to re-write the thermal history of the Moon.
Scientists have looked for work-arounds. For example, maybe the lava in Ina really is frothy and rubbly with lots of holes that by compacting under impact manage to skew the impact cratering statistics, effectively by absorbing the shock of an impactor and suppressing the resultant craters... and making it look younger than it really is. Great idea, but it doesn't actually work when you look at the details. So here we are in 2024 with this quote from the paper on the right : "Our analysis ... reveals additional conundra and enigmas that need to be resolved"... and I think they're right !
We've already looked at one issue regarding "water" on the surface of the Moon, but what about water locked up in the chemical structure of rocks inside the Moon ? It's been known since the analyses of Apollo samples, performed in 2008, that the rocks of the Moon are not bone dry. However, the samples concerned at the time were tiny glass beads that had condensed rapidly (chilled) from magma thrown upward as fire fountains that likely occurred all over at least the near-side of the Moon during the time that the Mare basalt lavas were being erupted (~3.0-2.0 Ga).
So ... what's new 16 years later in 2024 ?? Scientists have now found grains of the mineral apatite in a tiny meteorite that they have determined comes from the Moon : note the scale bar here. The importance of the apatite is that it is a complex Calcium Phosphate that contains OH, which tells us that there was water (H2O) around when the apatite crystallised.
If you think the meteorite is small, just look at the size of the apatite grain in this image, also from the 2024 paper !The importance of the meteorite is that it is not a piece of mare lava, It's a small piece of Anorthosite (the white stuff you can see naked-eye). More importantly it's a piece of ferroan Anorthosite, which means that it formed by the crystallisation of the Moon's magma ocean (not sure which one, cos apparently there were at least two !). That means that the water in this sample was present during the first ~200 My of the Solar System. Most importantly we now have to include the potential chemical effects of water in the collision model for the formation of the Moon ... and that may have very interesting consequences.
In 1936 people discovered the muon, a heavier version of the electron. It was so unexpected that a well known cosmologist famously declared, “Who ordered that"? Well, the same could be said for the Compton-Belkovich feature on the far-side of the Moon. According to a paper published in the summer of 2023, it's more or less round, ~50 km across and, according to microwave measurements ithas a heat flux ~20 times that of the surrounding anorthosite highlands. Now, there's not too many ways to account for this. Given the size of the heat source and the magnitude of the heat flux anomaly, scientists suggest that it has to be due to granite. Not a piece of granite, but an entire intrusion (bubble) of granite located just below the surface. That sounds like the Canadian Shield, or something from either the Appalachians in Nfld or New Brunswick, or the Canadian Cordillera in BC... but what's it doing on the Moon ? The Moon is not supposed to have granite ! On Earth the geological mantra is "No water ... no granite". Is this more evidence for even more water involved in the history of the Moon ? So here's yet another case of a relatively local feature potentially requiring that we take yet another look at how our Moon formed and evolved globally.
My last story concerns everyone who has a telescope, even a relatively small one : light coloured swirls of dust that are brighter than the background lavas. The largest and best known of these swirls is Reiner Gamma in southern Mare Procellarum, and is visible to amateur astronomers. The scale bar for the Reiner Gamma image is 100 km. Other examples include Mare Ingenii (~350 km across) and Firsov crater (~50 km). For all the world ... these swirls look like dust transported by wind storms, but of course that won't work on the Moon cos there's no air ! So scientists have tried coming up with models involving ...
- Temporary winds generated by impacting comets
- Dust migration induced by the solar wind
- Local magnetic fields that either induce migration of dust that contains nanometre-size Fe particles, or protects that dust from solar wind-driven migration !
- Interference between solar wind and local magnetic fields that generates a local electrical field that induces dust levitation !
- and topographical highs and lows, where dust becomes trapped and protected in the lows.
So I wish the Artemis program well ...
I just wish it wasn't sucking all of the air out of the room and distracting science journalism from what else is happening in lunar science. Many individual scientists and small teams are doing good science on the Moon ... and some are still wrestling with questions first raised up to a half century ago.
More power to them !
I just wish it wasn't sucking all of the air out of the room and distracting science journalism from what else is happening in lunar science. Many individual scientists and small teams are doing good science on the Moon ... and some are still wrestling with questions first raised up to a half century ago.
More power to them !
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