Rachel found Noughts disconcerting in principle, and Siloh more so. Most chose to have no hair, but Siloh sported a rim of kinked coils, glinting like brass, as if a halo had descended onto his skull. Pale eyelashes flicked seldom, gravely. Descending, the eyelids looked pink and rubbery. The nearly invisible blond eyebrows arched perpetually, so every word seemed layered with artifice, eyebrows punctuating as tones slid among syllables with resonant grace. The face shifted from one nuanced expression to another, a pliable medium in ceaseless movement, like the surface of a restless pond rippled by unfelt winds. She felt as though she should be taking notes about every utterance. Without blinking, she shifted to recording mode, letting her spine-based memory log everything that came in through eyes and ears. A simple click at her wrist did it. Just in case.

“I have not kept up, I fear,” she said; it was always a good idea to appear humble. “The incursion—”

“Has nearly reached Jupiter’s orbit,” Siloh said. The wall behind the Nought lit with a display showing the sun, gamely plowing through a gale of interstellar gas. Oort cloud satellites had framed it all in many frequencies.

Only recently had humanity learned that it had arisen in a benign time. An ancient supernova had once blown a bubble in the interstellar gas, and Earth had been cruising through that extreme vacuum while the mammals evolved from tree shrews to big-brained world-conquerors. Not that the sun was special in any other way. In its gyre about the galaxy’s hub, it moved only fifty light-years in the span of a million years, oscillating in and out of the galaxy’s plane every thirty-three million years—and that was enough to bring it now out of the Local Bubble’s protection. There was a vagrant molecular cloud coasting through the larger supernova-induced bubble. Astronomers hadn’t seen it coming and now here it was, knocking on the solar system’s door. The full density of interstellar hydrogen molecules and assorted debris now beat against the sun’s own plasma wind, pushing inward, hammering into the realm of the fragile planets.

“The hydrogen wall began to bombard the Ganymede Colony yesterday,” Siloh said with the odd impartiality Rachel still found unnerving, as though not being male or female gave it a detached view, above the human fray. “It is intruding at our local speed around the galaxy, two hundred thirty kilometers a second. We at the Library are instructed to do all we can to find knowledge bearing upon our common catastrophe.”

The wall screen picked up this voice hint and displayed Jupiter’s crescent against the hard stars. Rachel watched as a fresh flare coiled back from the ruby, roiling shock wave that embraced Jupiter. The magnetic fields that had once stood off the interstellar hydrogen, well beyond Pluto, detected in the early 2000s by the Voyager probes, now draped like gauzy veils around Jupiter’s own magnetic realm. These fought for primacy. The planet’s magnetic bow curve rippled with colossal turbulence, twisting vortices bigger than lesser worlds.