When one looks down through a UC Santa Cruz press release (see Grist below) the word “splats” does appear in a quote. But whether the term “Big Splat” is purely the press officer’s concoction, or was the professor of earth and planetary science’s idea, one cannot tell. But Big Splat is how a new wrinkle in the leading explanation for our Moon’s formation is, in most accounts, making its news debut. (Late amendment – see AP’s story, and NPR;s too, below for hints to the term’s etymology).

The paper, in Nature by a Santa Cruz professor and his post-doc (now at a Swiss institution), seeks to explain the lopsided lunar terrain. The Moon’s far side sits at higher altitude and is more rugged than the one we see from Earth. A merger could explain it. The idea builds on what has become, in recent decades, the leading explanation of the Moon’s genesis. That could well be called the Humongous Splat – the grazing collision by the young Earth with a Mars-sized protoplanet. The wreck left a belt of debris circling Earth, but without much of our iron core included. The belt eventually re-contracted into our Moon.

The new detail is that an intermediate step left two moons of different size following one another in pretty much the same orbital path, held in place for a few tens of millions of years like a Trojan asteroid and I’m unsure how that works. Eventually they drew together. They struck at 5000 miles per hour or so. To  scale, that is slow. It’s nothing like two airplanes smacking. At that speed it’d take about twenty minutes for one of these orbs to get past the other in a near miss. A big spray of debris and magma would rise from the collision – the yellow stuff in the upper image from computer simulations. But rather than smithereens all over the place, the moons’ bulks would deform plasticly and join.  The result would be the smaller adding itself to the larger one  as a hump on one side. The whole schmear would settle to near spherical shape. But a vast, raised, beat-up hemisphere would be left just like on the Moon we now see. Interestingly, it is surmised that when the collision occurred the larger body it still held a sea of magma 50 miles or more deep just under a thin solid crust due to remnant heat and volcanism from its own initial formation. Most of that magma would have sloshed to the other side – the one we see today. It’s called KREEP, and it has been a mystery why so much more is on one side of the moon than the other.

Big Splat is not a bad term. It is also likened, in the the AP account listed below (error note: this post initially credited the press release) to a cream pie in the face – meringue all over the place but no broken bones. Still – reporters do not HAVE to accept the press release’s Big Splat metaphor. Most do, a few do not. Big smoosh, lunar merger, dirty dancing (?), lots of terms might do as well. Upcoming space mission, including possible rock sampling, may settle whether our Moon was once two.

Stories:

• AP – Seth Borenstein: Earth’s two moons? It’s not lunacy, but new theory ; (It’s really a hypothesis, not that this is a usage battle that’s winnable. But overuse of “theory” to mean almost any half-plausible idea is why evolutionists will never beat down the “it’s only a theory” jibe from scriptural literalists.) Seth gets the quote straight from the lead author: “This big splat is a low-velocity collision.” So, the term has the PhD’s endorsement. Perhaps he invented it. Borenstein gets a quote from a man most associated with the impact theory of the Moon’s formation too.
• Reuters – Steve Gorman: Earth’s moon shaped by impact with another – study ; Good for him, or else he just didn’t read the press release and that’s somewhat commendable too. No Big Splat in sight.
• Independent (UK) Steve Connor:  The big Splat: collision may have created lopsided Moon ;
• Sydney Morning Herald – Deborah Smith: The moon’s dark secret – it once had a sibling ; Just the facts, no Big Splat.
• PostMedia News via Montreal Gazette – Beatrice Fantoni, Jordan Press: ‘Big splat’ could explain different topography on far side of moon;
• NPR – Nell Greenfieldboyce: Early Earth May Have Been Orbited By Two Moons ; Ah, here one can hear the lead author recalling wondering .. about a big splat. So there. Looks plausible that the press officer, an old pro too, heard it from the professor first. Greenfieldboyce adds that this was so long ago it was before life – Earth was largely molten at the time. Two moons perhaps – but nobody and no thing saw them.
• Universe Today – Nancy Atkinson: Second Moon May Have Orbited Earth Billions of Years Ago ;
• ScienceNOW – Richard Kerr: Did a Slo-Mo Crash Create the Two-Sided Moon? ; As did Borenstein, Kerr calls up one of the originators of the Earth-collision scenario. Nice job, no splatting.
• Nature.com – Richard Lovett: Early Earth may have had two moons ;

Grist for the Mill: UCSC Press Release ;

- Charlie Petit

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