Last week Linda and I were on Arran, staying at a Vegan b & b called ‘Alice’s Wonderland’ – highly recommended, and suggesting an overall title for the most recent lunar news, just when I thought it was safe to come out of the moonlight
First was the story ‘The Face of the Moon: How Old Is It?’ (ON, July 13th 2023). It gave revised dating for the big impact basins on the side of the Moon facing the Earth, pushing them back from 3.9 billion years – the date suggested by the returned samples from the Apollo missions – to nearer 4.1 billion years, within the Final Bombardment in the formation of the Solar System as it is today.
Around a billion years later, those Nearside basins filled with dark volcanic basalt, high in titanium content compared with the anorthositic rock of the surrounding lunar highlands, lighter in tone due to a larger content of aluminium. It’s not clearly understood what was going on within the Moon at the time, and particularly why most though not all of the impact features on the Farside weren’t similarly filled (Fig. 1). It’s particularly strange that the huge Aitken Basin on the Farside remained unfilled, when smaller craters on and around its rim were flooded with lava and have smooth, dark floors (Fig. 2). To explain how strange things have now become, I need to recap on some of the recent lunar articles here.
In The First Men in the Moon, H.G. Wells portrayed a lunar interior with plentiful air and water, freezing at night where it escaped to the surface, liberated during the 14 Earth days of sunlight (Fig. 3).
Such a temporary atmosphere would have been easily visible from Earth, if it existed. The instruments left on the Moon by the Apollo astronauts detected a very much thinner temporary atmosphere of heavier gases, briefly enhanced by emissions from the Lunar Modules. The last three Command Modules had Scientific Instrument Bays which studied the Moon intensively from orbit, looking in particular for gases such as radon, emitted by radioactive materials, and finding areas on the Nearside of the Moon which had more radioactivity than any known Earth rocks, as well as deposits on the Farside, particularly at the Van de Graaf crater which is now being explored by China’s Yutu-2 rover. But those studies were limited to the three bands around the equator which were overflown by Apollos 15, 16 and 17 (Fig. 4). NASA wanted to send an Apollo without a lander into lunar polar orbit, to extend the mapping to the whole of the Moon, but was never allowed to do so.
The need wasn’t met until 1998, when NASA put the Lunar Prospector mission into orbit (Fig. 5). Its main mission was to confirm the hints of water in shadowed craters at the lunar poles, which had been detected by the Clementine orbiter in 1994. (Note the continuing prospector theme: the original Lunar Prospector was a surface rover, cancelled in the 1960s.) But the orbiter also carried new versions of the SIM Bay instruments, and among other achievements it mapped the distribution of radioactive thorium in the lunar crust. It proved to be spread across the whole of the Aitken Basin, but there was also one isolated concentration of it near the north pole on the lunar Farside – top left of the right-hand image (Fig. 6).
That region had been imaged before. In 1992, the Galileo spacecraft flew past the Earth and Moon on its way to Jupiter, and discovered the Aitken Basin, so large that it had previously been missed (‘The Earth from Space’, ON, 7th May 2022). It also detected the thin atmosphere of water vapour over the sunlit face of the Moon, generated by interaction of hydrogen nuclei in the Solar Wind with oxygen in the surface rocks. H.G. Wells wasn’t so far wrong, but the finding seemed so unlikely that it wasn’t headlined until confirmed by India’sChandrayaan-1 in 2009 (Fig. 7).
But Galileo’s multispectral cameras also provided a visual beginning of the geological mapping of the Moon to be followed up by Lunar Prospector – initially for the whole Moon from a distance (Fig. 8), then for the northern hemisphere from closer to (Fig. 9).
And beyond the north pole of the Moon, on the edge of the terminator with lunar night in Fig. 10, Galileo photographed a light-coloured region which is now called Compton-Belkovitch (Figs. 11 and 12).
Photographed in detail by Lunar Reconnaissance Orbiter, it’s unquestionably volcanic (Fig. 13), still a hotspot, 20 times warmer than the surrounding surface, and its location coincides precisely with the thorium-bearing region detected by Lunar Prospector (Figs. 14 and 15).
But now, detailed study of it using data from the Chinese Chang’e-1 and Chang’e-2 orbiters has revealed that it’s what’s called a ‘basolith’: a magma chamber heated by radioactive decay, breaking through to the surface from below, and under that a much larger chamber, multiply melted and differentiated by successive episodes of heating, like similar features at Yellowstone Park and in Alaska (Fig. 16). It’s not a trivial feature, 31 km in diameter, and what’s most extraordinary is that it’s not basalt, like the dark floors of the lava-flooded craters, but granite, formed in the presence of water. (Diana Lutz, ‘Moon Heat Anomaly Appears to Be a New Form of Lunar Volcanism’, Washington University in St. Louis, Newsroom, 24th July 2023.)
The samples of those basalt lavas brought back by the Apollo missions appeared to be completely lacking not just in water but in all volatile elements and compounds, suggesting that they had been completely dispersed in the collision with a Mars-sized body which formed the Earth and Moon as we know them. The discovery of ‘rusty rock’ in Apollo 14 samples was put down to contamination after they were brought to Earth. But the analysis of moonrock by NASA was stopped by the US Senate and Congress after it was given a ‘Golden Fleece’ award for pointlessness by the notorious Senator William Proxmire of Wisconsin, who believed that all funds for space research should be reallocated to subsidies for the farming states. (At one time, space enthusiasts could buy car bumper stickers which read, ‘Anyone who buys Wisconsin cheese is a traitor to the human race’.) When I visited the Lunar Receiving Laboratory on my visit to Houston in 1986 (‘Eyewitness to History: Shuttle Trainer’, ON August 14th 2022), over 80% of the returned moonrock remained unexamined and the whole complex was empty except for two small university research teams (Fig. 17). Now that the brakes are off and almost all the moonrock has been examined, except for a percentage kept back for study by future methods, it turns out that not just the ‘rusty rocks’, but also the ‘orange soil’ glass beads of Apollo 17 and the green beads of Apollo 15, all formed deep below the lunar surface in water-bearing rock. Almost the last advocate for the existence of such layers was the Arran-based astronomer V.A. Firsoff, though there are not likely to be lakes down there as he suggested (Strange World of the Moon, 1959).
However, the discovery is highly anomalous, and highlights still another lunar anomaly which may now come into focus. In 1966-67, in preparation for the Moon landings, NASA launched a series of moonprobes called Lunar Orbiter, to photograph the lunar surface in detail, particularly the proposed landing sites (‘The Lunar Farside’, ON June 4th, 2023; ‘More Lunar Anomalies, Part 1’, June 25th 2023). One of their major discoveries was the existence of ‘mascons’, mass concentrations below the lunar surface and concentric with the big impact basins. A first thought was that they must be the remains of the impactors which had formed them. But attempts to mine a similar body of nickel-iron under the Barringer Meteor Crater in Arizona drew a blank: though the crater was surrounded with iron fragments, the main mass of the asteroid had completely vaporised. The mascons are thought to be upwelling deposits of magma, from deep within the Moon, from which the impact basins were flooded – though their preference for the lunar Nearside remains mysterious, as above.
And if they all came from a single layer within the lunar mantle, below the thick lunar crust, how are we to explain the existence of ‘negative mascons’, less dense than the surrounding lunar features? They’re not easy to identify in the NASA guides to the last two Apollo missions (Fig. 19; Gene Simmons, On the Moon with Apollo 16, NASA EP-95; On the Moon with Apollo 17, NASA EP-101, US Government Printing Office, April and December 1972), and I’ve found very little about them since.
One example is Sinus Iridum, the Bay of Rainbows (Fig. 20), at top left of Fig. 19, and another is Mare Vaporum, photographed by Apollo 15 (Fig. 21). The late Jean Sendy, who translated my Man and the Stars into French (À L’Écoute des Galaxies, Robert Laffont, 1976), had some very colourful ideas of his own, particularly that the entire Old Testament was a misinterpreted account of extraterrestrial Contact in the Old Middle East. According to Jean, God’s statement that he had placed the rainbow in the sky was a metaphorical account of creating an alien base in a huge cavern below Sinus Iridum – all of it based on wordplay, because the French for the rainbow is l’arc en ciel, and that ‘had’ to be a link between the Ark of the Covenant and the Bay of Rainbows on the Moon. His account in The Age of Aquarius makes entertaining reading, especially in the original (L’ère du Verseau, Robert Laffont, 1970), but I’m glad that he wasn’t around for publication of my Children from the Sky (Mutus Liber, 2012), because he would undoubtedly have insisted that Sir Herbert Read was right in his novel The Green Child (1935), where he placed the children’s origin in a mysterious sealed cavern (without lunar gravity).
The late John Braithwaite suggested much more plausibly that the negative mascons are simply upwellings of lower-density rock, perhaps from different levels than the ‘regular’ mascons. Will they, too, turn out to be granitic? If so, you read it here first.
Before we leave the topic, however, a new lunar anomaly has been found by Neal Spence and highlighted by George Malcolm through the Google Group New-SPSR, the Society for Planetary SETI Research. The crater Petavius B, a secondary crater within Mare Fecunditatis, the Sea of Fertility (Fig. 22), shows some very interesting features, including pits which resemble those found on Mercury, where soft metals have apparently vaporised at the surface when exposed to sunlight (Fig. 23).
Within it there’s what appears to be an exaggerated version of the 3-sided pyramids on Mars which Carl Sagan was first to point out on Mariner 9 photographs, and have since been found in 4-sided and 5-sided versions in the Cydonia region, along with the famous ‘Face on Mars’. Similar ones are found on Earth, particularly in the Sahara, but very much smaller. They are apparently formed by wind erosion over very long periods – but on the Moon? In the wake of the Compton-Belkovitch discovery, Petavius B definitely merits further investigation.