Earth’s crust bears the scars of bombardment by shattered cores of failed planets

Isn’t it funny how often things “everyone knows” turn out to be just part of the story? This might be stretching the definition of “everyone” a little bit, but bear with me: It’s been scientific consensus that much of the material that hit the Earth during the Late Heavy Bombardment came from the belt of asteroids and other detritus between Mars and Jupiter. But at the most recent meeting of the American Astronomical Society, Dr. William Bottke presented details from his ongoing research on the Earth’s history of getting smashed with debris. According to Bottke, of the Southwest Research Institute, not all of what hit us came from where we think it did.

“We have evidence for two early-bombardment populations and a time difference between them — a late one, plausibly made by escapees from the asteroid belt, and an early one from elsewhere,” Bottke told Space.com. By “elsewhere,” he means from a population of failed planets whose cores never got the chance to become fully formed. Instead, those monumental hunks of rock drifted away from where they formed. And some of them, Bottke argues, smashed into the Earth.

It all started with craters that dated to the LHB, but appeared to have come from an implausible angle. “Running the clock back” showed Bottke that these impactors were striking Earth and the Moon at all the wrong angles to have come from the asteroid belt. Instead, Bottke believes that the evidence shows a different origin for much of the debris that struck us during that earlier bombardment.

The LHB went down not quite a billion years into the life of our planet, and lasted some 2-300 million years. During that time, a great deal of rocky debris still circulated in our inner solar system, some of which was left over from early days: great big rocky agglomerations that had started to coalesce into the cores of planets, but never really made it the whole way. During the complex dance of planets that pushed away Saturn, Uranus, and Neptune and brought Jupiter slowly sailing in from the periphery, the planetary might-have-beens that hadn’t yet deorbited or been flung away were shoved into new orbital configurations. When Earth came passing through all that protoplanetary debris, Bottke argues, some of it came crashing down on our planet.

Bottke is an expert on the Late Heavy Bombardment, and much of his recent research on the LHB has been enabled by a development called the Nice model. That narrative of the solar system’s development points to a late migration of gas giants, mostly outward, in order to explain the current arrangement of planets and other mass orbiting our sun.

Among the other things Dr. Bottke has done over the years is research into the K-T impact: the cataclysmic asteroid impact some 65 million years ago, that signed the death warrant of the dinosaurs and ushered in the age of the mammals. Bottke and his colleague David Nesvorny, also of the SwRI, have traced the physical impactor from that event 65 million years ago to the breakup of the hundred-mile-wide main belt asteroid Baptistina, some 160 million years ago.