Replies

V.A. Firsoff (Valdemar Axel Firsoff, as it turns out) wrote a lot of books (I think he's dead, but perhaps not), including Strange World of the Moon published back in 1959, ten years before the manned landings started, and even before the first robotic landers.

I picked up a used copy for $1.98 at the enormous chain bookstore, which had "Shimon Kaplan, Israel" on the flyleaf or whatever that blank first page is called. Hard to figure, considering this is Grand Rapids Michigan, but it's not exactly like a message in a bottle.

Firsoff's book is interesting in that it shows the prevailing ideas about what would be found on the Moon (it was already believed during the 19th century, and more relevantly, by the 1920s and 1930s in Germany, that humans would visit the Moon). In a chapter "The Earth's Fair Child or a Foundling?" discusses the concept of the birth of the Moon via an overspin (doesn't use that word) condition on the Earth, which appears to be his view.

Firsoff blows off the idea that impact plays any role on the Moon, attributing its surface features to vulcanism, a view that died a quiet death in 1972, when a geologist first set foot on the Moon.

Firsoff attributes lunar craters and other features to the Moon's capture by the Earth (as well as contraction of the lunar sphere), apparently after having been tossed off by the overspin condition very early in the history of the Earth. He appears to envisage three encounters between the formed Moon and the Earth, resulting in temporary capture twice leading to the eventual outright capture.

...the Moon clearly could not have been the satellite of the Earth then, for a total period of about 2,000 million years... Spurr points out that the face of the Moon shows two systems of great surface fractures, or faults, lying about 30 degrees from the two poles and trending from west-south-west to east-north-east. This is explained by him as a result of the halting of the Moon's rotation... Curiously, the face of the Earth, too, shows a similar structure, with the same general trend -- the Highland Boundary Fault... The poles of the Earth would also seem to have shifted place on at least three occasions, in the Cambrian, Permian, and (lastly) Quaternary Periods, brining ice and cold to previously warm lands... some mighty force made the crust of the Earth slip (the rotational stability of the axis of a mass as large as the Earth is enormous) and the position of the poles wobbled... there exists on the Moon a triple grid of surface fractures... perpendicular to each other within each grid, the grids being of different ages... Cambrian, Perm-Carboniferous, and Tertiary.

Fascinating idea, based though it is on outmoded ideas about impact (i.e., Firsoff's view that there was no role for impact). He's basically given us a snapshot of the problems inherent with a fission origin (either by overspin or by impact), not least of which is that the fission origin also requires in orbit formation of the lunar sphere and capture by the Earth, while showing that capture is possible.

One more thing from Firsoff:

Unlike any other satellite, the Moon completes her revolution round the Earth outside the sphere of the latter's gravitational predominance. Solar and terrestrial gravity draw level with each other at the distance of 161,800 miles from the center of the Earth, whereas the Moon never comes any nearer it than 221,463 miles.

But I dunno if this is true. Objects in prograde orbit around the parent body will accelerate and thus raise altitude, while those in retrograde do the opposite. So, a body in orbit could wind up in escape, particularly if a third body were givin' it a come-hither.

Note: this topic is from 10/04/2004.

The number of asteroid impacts to the Moon and Earth increased by two to three times starting around 290 million years ago, researchers reported in a paper in the journal Science.

They could tell by creating the first comprehensive timeline of large craters on the Moon formed in the last billion years by using images and thermal data collected by NASA's Lunar Reconnaissance Orbiter (LRO). When the scientists compared those to the timeline of Earth's craters, they found the two bodies had recorded the same history of asteroid bombardment -- one that contradicts theories about Earth's impact rate.

For decades, scientists have tried to understand the rate that asteroids hit the Earth by carefully studying impact craters on continents and by using radiometric dating of the rocks around them to determine the ages of the largest, and thus most intact, ones. The problem is that many experts assumed that early Earth craters have been worn away by wind, storms, and other geologic processes. This idea explained why Earth has fewer older craters than expected compared to other bodies in the solar system, but it made it difficult to find an accurate impact rate and to determine whether it had changed over time.

A way to sidestep this problem is to examine the Moon. Earth and the Moon are hit in the same proportions over time. In general, because of its larger size and higher gravity, about twenty asteroids strike Earth for every one that strikes the Moon, though large impacts on either body are rare. But even though large lunar craters have experienced little erosion over billions of years, and thus offer scientists a valuable record, there was no way to determine their ages until the Lunar Reconnaissance Orbiter started circling the Moon a decade ago and studying its surface.
Moon Data Reveal Large Increase In Asteroid Impact History | Lonnie Shekhtman | NASA's Goddard Space Flight Center | SciTechDaily | January 17, 2019