The mess wasn’t crowded when Wernstecki arrived. Merlin and Vicki were at a corner table. Tanya, Vicki’s cabin mate was with them. He helped himself to a Mimas tea from the self-serve counter by the door and made his way over. A few heads nodded at him perfunctorily. “So what’s going on?” he asked, easing himself down onto the bench seat next to Tanya.
“Vicki’s latest exchanges with Farzhin at Dione,” Merlin replied. “It sounds as if they’ve got something coming together that could tie it all up. We thought you’d want to hear it.”
“Me too. I’ve only just arrived here,” Tanya put in.
Wernstecki sipped his tea. “Well?” He looked around invitingly. “I’m all ears, and panting with suspense.” Merlin waved for Vicki to take it. Wernstecki had heard a lot about Vicki as a result of working with Keene on Titan, and gotten to know her himself more during the voyage. She possessed the instincts that made her a natural Kronian too.
“Emil’s working with Sariena’s people now,” Vicki said. “They’ve been modeling large-scale impacts on internally hot, planet-size bodies. What comes out is consistent with a lot of what we believe happened.”
“What are we talking about—the breakup of the Saturnian configuration?” Wernstecki asked.
Vicki shook her head. “Before that. The earlier event. If they’re right about Earth being part of a family accompanying a proto-star Saturn, it could have been during the disruption when they encountered whatever the original solar group was.”
“They think this is the event that ended the dinosaurs,” Tanya said.
“So that didn’t happen with the breakup?” Wernstecki checked.
“Not if this latest theory is right.”
It was generally accepted that Earth’s gravity had undergone a significant increase at some point—things the scale of dinosaurs couldn’t have functioned under modern conditions. Many attempts had been made to fit this with the time of Earth’s separation from Saturn; the hemisphere phase-locked to face the primary would have experienced a gravity reduction, reverting to full value when Earth became detached. The two problems that this approach had run into, however, were first, no amount of tweaking with the model gave a gravity increase sufficient to account for the effects that had been inferred; and second, it was known that humans had lived at the time of the Saturnian breakup, which was difficult to reconcile with the presence of dinosaurs.
Vicki explained. “It seems there might have been two distinct events. To begin with, Earth was a close-orbiting satellite with reduced gravity on its Saturn-facing side. This produced gigantic life-forms. They lived on a crustal bulge, also a result of the distorted gravity, that stood out from the ocean covering the rest of the planet. A super-continent.”
“Pangea,” Wernstecki supplied.
“Now, a planet like Earth isn’t brittle all through,” Vicki said. “It’s a crust covering a fluid and sticky interior. An impact by something large isn’t going to shatter it into pieces. It’ll penetrate and be absorbed to produce a deformed composite body. Imagine Pangea on the far side, fractured by expansion of the opposite surface as the impact shock propagates through.”
“How big an object are we talking about?” Wernstecki asked.
“We put it at around twenty percent the volume of the previously existing Earth, and high density—about halfway between that of the crust and the core.”
“So you’d get a what? A kind of pear-shaped object?”
“Which over time collapses back to spherical. The increase in radius is small compared to the gain in mass, so surface gravity goes up appreciably. With the figures they used, new animals repopulating the changed environment would have to reduce their body dimensions by around forty percent to retain the same power-weight ratio.”
“Is that enough?” Wernstecki looked around questioningly.
“About what you’d need to produce the titanotheres,” Vicki answered, referring to the giant mammals of the Pleistocene. Wernstecki nodded. He seemed impressed that it was that large.
“But it gets neater, Jan,” Merlin Friet said. “A really economic theory. One cause ties together a whole bunch of things that didn’t seem related before.”
“Well, so far we’ve wiped out the dinosaurs and broken up Pangea,” Wernstecki agreed. “What else is there?”
“Just about all of plate tectonics,” Vicki said. “We know that the movements measured before Athena were just the final, cooling-down phases of processes that once happened a lot faster, and the old time scales of millions of years based on them were wrong. But that also means that shifting whole continents around the globe in a reduced time took something more than the tugs from a passing body that caused the sideways rifting Earth is seeing now.” She gestured toward Wernstecki. “You said it yourself a moment ago, Jan. Pear-shaped. The whole hemisphere that the pieces of Pangea are adrift on is elevated way above the surface mean. They slide down the gravitational gradient on layers of molten magma produced by dissipating all the heat.” Vicki tossed out a hand casually, as if the rest shouldn’t need adding. “And as the shape recovers back toward spherical, surface area shrinks with respect to volume, and crumples. That could give you mountain-chain building and ocean trenches.”