The new theory, introduced by University of California at Santa Cruz professor Erik Asphaug, posits that the distinct difference between the two sides of the moon, long debated by scientists, could have been caused by a low-speed collision between the current moon and a former sister moon about 1/30th the size of the current moon, with the former sister moon "squishing" on impact and then being flattened by gravity along the far side of the current moon, accounting for the different geology.
The NPR story can be heard by following this link, and a transcript of the story can be found at this location. Slightly more detailed descriptions of Professor Asphaug's theory can be found elsewhere on the web, such as this story describing the appearance of the theory which was published in the journal Nature yesterday.
Professor Asphaug's new theory proposes that both moons -- the current moon and the erstwhile sister moon -- were formed when a "Mars-sized protoplanet smacked into Earth late in its formation period" (Naturenews article linked above). This event scattered debris into space, some of which "coalesced to form the moon" but some of which was left over, enough to form a sister satellite only 1,000 km or so in diameter.
This second moon, according to the theory, may have coalesced and remained at one of the Lagrange points ahead of or behind the earth on its orbit. We have discussed the importance of Lagrange points in this previous post describing the first actual (rather than speculative) space rocks definitively proven to be orbiting the sun along earth's same path in one of these Lagrange points.
According to the theory as described in the Naturenotes article, "Such a moon could have survived in a Lagrangian point long enough for its upper crust and that of the Moon to solidify [. . .]." However, as Professor Asphaug explains, tidal forces from earth and the gravity from the sun tend to disrupt bodies in these Lagrange points over time. "The Lagrange points become unstable and anything trapped there is adrift," he says.
The smaller moon collided with our remaining moon, but because they shared an orbit, the collision was relatively slow, and resulted in more of an event "like a mud clod thrown at a wall," as Dr. Asphaug says in the NPR interview. "You end up with a pancacke," he says.
We commend Dr. Asphaug for looking at the conventional explanations for the differences between the two sides of the moon and wanting to come up with something better, perceiving the current theories to be lacking. We also agree that the current theories are lacking, and noted that the very different features on the two sides of the moon cause a real problem for conventional theories in this previous post on the subject.
However, as with any other theory purporting to explain the existing evidence (including, of course, the hydroplate theory), we believe that due diligence is required rather than unquestioning acceptance (NPR may not be the forum for airing critical examinations of new scientific theories; in any event, NPR's story contained none). In the case of this new proposed explanation for the origin of the moon and its current surface appearances, there appear to be several thorny questions which may mitigate against its ultimate acceptance.
First, the idea that our moon originated from an ancient collision from a "Mars-sized protoplanet" has some problems. As Walt Brown, author of the hydroplate theory, points out in his book (which can be read in its entirety online here), many principles of physics appear to rule out an earthly origin for the moon. In the section of his book on the Origin of the Moon, he argues that:
The Moon could not have spun off from Earth, because its orbital plane is too highly inclined. Nor could it have formed from the same material as Earth, because the relative abundances of its elements are too dissimilar from those of Earth. The Moon’s nearly circular orbit is also strong evidence that it was never torn from nor captured by Earth. If the Moon formed from particles orbiting Earth, other particles should be easily visible inside the Moon’s orbit; none are.
Some claim that the Moon formed from debris splashed from Earth by a Mars-size impactor. If so, many small moons should have formed. The impactor’s glancing blow would either be too slight to form our large Moon, or so violent that Earth would end up spinning too fast. Also, small particles splashed from Earth would have completely melted, allowing any water inside them to escape into the vacuum of space. However, Apollo astronauts found on the Moon tiny glass beads that had erupted as molten material from inside the Moon but had dissolved water inside! The total amount of water that was once inside the moon probably equaled that in the Caribbean Sea.
These are powerful arguments and not well-understood by the public (if they were, then presumably NPR and Naturenotes would spend more time explaining how the speculative ancient impact was able to create a moon with the properties we see today, let alone how it was able to create two moons).
Another problem not addressed in that particular section of Dr. Brown's book but apparent from his examination of the origin of asteroids is the density of earth's current moon. This web page from NASA's Jet Propulsion Laboratory lists the densities of many objects in the solar system, including earth's moon, which turns out to be among the densest bodies in the solar system, at 3.344 grams per cubic centimeter (on average). No other moon in the solar system, except for Jupiter's Io, is as dense, and in fact most planets are less dense as well.
This is important because, as we discussed in the blog post about the origins of asteroids in the solar system, many of the asteroids (especially those that are large but not very dense) are probably examples of bodies that actually did coalesce from matter ejected from the earth -- not ejected by the collision of a Mars-sized protoplanet, but ejected during the rupture event that initiated a worldwide flood. Those with high densities similar to the density of earth's crust are probably single rocks, but those with lower densities (such as Ceres, with a mean density of only 2.077 grams per cubic centimeter) are probably loosely-packed clusters of smaller rocks, held together by their own weak gravity as well as by the presence of frozen water which was also ejected from earth during the same event.
Dr. Brown argues that the irregularly-shaped moons of Mars, Deimos and Phobos, are probably similar low-density composite asteroids held together in the same way. Indeed, the mean densities of Deimos and Phobos (as can be seen in the previously-linked NASA Jet Propulsion Lab data tables) are only 1.471 and 1.872 grams per cubic centimeter, respectively. These facts would appear to argue that the earth's moon is not a coalescence of smaller rocks that were ejected from earth by a collision from a Mars-sized protoplanet.
Further, Dr. Asphaug's new theory does not appear to give a satisfactory explanation for the fact that almost all of the largest craters on the moon are on the side which faces the earth. As we already discussed in the blog post which shows that the hydroplate theory gives a good explanation for the distinct features of the moon's surface, it is very difficult to argue that large traveling space rocks avoided the dark side and swooped around to a position between the earth and the moon before turning back towards the moon and hitting its surface. It is much more likely that these large craters facing the earth are the result of large chunks of debris striking the moon after the violent eruption of the rupture that led to the flood.
On the other hand, a slow-motion impact resembling "a mud clod thrown at a wall" in which the smaller moon "kind of splats" (in the words of Professor Asphaug) would not appear to be a likely candidate for throwing up large pieces of debris which then came back to impact on the other side of the moon from the "splat." And yet the fact remains that many large objects appear to have hit the near side of the moon and not the far side, unless we were to argue that the larger craters on the far side were later covered up by the "splat" of the second moon (this explanation leaves the problem of the few large craters that are found on the far side, presumably occurring after the splat).
In short, the new theory of a second moon may have some data which argues against it. However, it is important to reiterate that putting forward bold new theories is commendable, and Professor Asphaug and his colleagues should receive recognition for examining the evidence and coming up with a creative explanation that may tie the data together more coherently than theories which came before.
Personally, I believe that the evidence on the surface of the moon -- which does pose an ongoing problem for scientists -- is much more coherently explained by the events described in the hydroplate theory. Additionally, while the new "second moon theory" relies upon some speculative events for which there is little or no evidence and against which the principles of physics appear to argue, such as the assumption of a Mars-sized ancient impactor to get the entire timeline started, the hydroplate theory is corroborated by literally hundreds of other pieces of evidence around the world and indeed throughout the rest of the solar system.
Additionally, the hydroplate theory provides compelling new insight into the extensive evidence found in the human timeline, evidence that has mystified mankind for centuries and which contradicts other conventional theories of the past, as well as provoking alternative theories galore. The examination of the way that the hydroplate theory appears to be supported by evidence from ancient mythology and archaeology is discussed in the Mathisen Corollary book, the first book to apply the hydroplate theory to extensive "human evidence" of this sort.
Again, we have the greatest respect for Professor Asphaug and his thirst for the truth. This is the kind of spirit that needs to permeate the search for answers, in astronomy, geology, biology, and anthropology. All such theories, including those that I offer in my own book and in this blog, should be critically examined in the very same way by many others, who will necessarily have different talents, backgrounds, and areas of specialization. The entire attitude we should all maintain might best be summed up by the current spokesman for Dos Equis beer, who advises his listeners, "Stay thirsty, my friends."