wait, can planets reproduce by budding?
Well, according to a paper by a physicist and a geologist who propose that a bubble of molten heavy metals was ejected from a young Earth after a nuclear meltdown within its innards and formed the Moon, they could. Forget the notion of a wandering world plowing into our planet and ejecting the material which would become our natural satellite, even though we have evidence that collisions happen in young solar systems. Imagine a spheroid of molten rock wildly spinning around its axis. As molten uranium and thorium churn close to what would be its equatorial plane, they trigger a runaway nuclear reaction until a planetary meltdown belches out a plume which cools into the Moon. Okay, I’m sure they have a reason to reject the mainstream consensus…
Let’s think back to the impact theory. When an object delivers a glancing blow to the young Earth, it sends our planet whirling around its axis, and as it does, a spray of superheated rock is shot where the Moon will form. But apparently, there’s a problem with this scenario and for the authors, the proposed solution to this problem just isn’t good enough, which is why they resurrected the fission spin-off hypothesis from its slumber. Models suggest that around 80% of the Moon’s make up should’ve come from the impacting planet. However, it has a lot more in common with the Earth in terms of composition. The current explanation is the mixing of the rocks right after the impact, while the proto-Moon was still molten and coalescing. But to Rob de Meijer and Wim van Westrenen, this seems a little too convenient. Instead, they argue that the chances of a close match between our planet and an alien world at the dawn of the solar system is highly unlikely, especially in the levels of such heavy elements as uranium, chromium, neodymium and tungsten.
Now, having the Moon spun out of a proto-Earth would account for the similarity in their composition, but you’d need a rather bizarre arrangement for this to happen. Our young planet would need to be very distorted, twice as wide around its equator as it would be around its poles. A day on this planet would be only 2 hours and 18 minutes long. There doesn’t seem to be any proof this would happen and the only supporting evidence used by de Meijer and van Westrenen is math showing the energy and momentum of their hypothetical early Earth and the newly formed two body system, and the similarities between rocks on the Moon and Earth rock with a few traces of the key elements they say will clinch the case. Well, assuming of course that planets in a similar range of orbits can’t form from very similar elements and have a similar composition that could mix in the kind of blast thought to have created the Moon, a concept that’s oddly missing from their paper.
And that’s the big problem with de Meijer and van Westrenen’s proposal. It seems very over-thought and uses a 150 year old idea formed when we had no proof of planetary collisions instead of trying to work out if planets coalescing from similar materials could have a similar composition and to what degree before slamming on the brakes and starting from scratch on a proposal that would be incredibly difficult to prove. And considering that we already have an example of planetary collisions, it seems like an awfully big step back to reconsider a concept from the Victorian era just to start the whole scientific process from scratch…
See: R. de Meijer, & W. van Westrenen (2010). An alternative hypothesis for the origin of the Moon, submitted to Earth, Moon and Planets arXiv: 1001.4243v1
The moon seems to be comprised mostly of silica crust materials with small to moderate incursion to Earth’s mantel layers. Common dating of isotope ratios seem to clearly indicate that moon-stuff is in fact Earth-stuff (or formed at the same time). However, Impact models seem a much better fit to the data than “budding off” models.
Looking at the arxiv paper, I note it was submitted in a rather low impact journal over a year ago, but not published. A quick perusal of the article itself reveals some pretty simple mathematics that are at best back of the envelope for such a model. For instance binding energy is calculated to be strictly from assembly from infinite distance of constituent parts. Nothing about cohesion or various moduli is mentioned (at first glance) but alluded to in how they chose as a materials properties to be quartz. Even best case scenarios show that angular momentum of a proto earth is insufficient.
And here enters in a “big burp” theory on a “georeactor” of approximately 120 km in radius going super critical and blowing a chunk out of the Earth. At this point they seem to forget the spin rate of the Earth, and how that would play hell with any sort of local conglomeration of fissionable material according to their own model.
In any rate, I would love to see the discussion between the authors and the journal referees. =)
Honestly, I wouldn’t want to publish this paper if I were a journal editor. There are just too many questions that are left unanswered. How can they prove that it’s impossible for planetary siblings formed from mostly the same elements are unlikely to share a number of close similarities in composition? What would make a proto-Earth spin at a rate about ten times faster than today? Did the same happen to Mercury, Venus or Mars? How would we know if the answer to that is yes?
Maybe I’m being evil, but I just don’t see that paper surviving through any peer-review process since it has more holes in it than a pasta strainer…
Indeed, this seems fishy. Basically, their argument is that the existing impact theory has a flaw because of the estimated 80 original bolide/20 earth distribution of the post-impact material that formed the moon. The logic seems to be, with 80% coming from the impactor, the odds that it would be so isotopically identical to earth are minimal. Hence, the impact theory is flawed.
What they don’t fully consider is that the most logical explanation is that the 80/20 split, which derives solely from computer modeling, is the problem. Ground truth from the Apollo rocks shows us remarkable isotopic homogeneity. Ergo, moon material = earth material. If a computer model suggests most of the moon came from the impactor, that’s the assumption to challenge.