There had been only a handful of visitors in the fifty years since the building of the Poole wormhole. None of them had troubled to walk the surfaces of Pluto or Charon. The wormhole, Lvov realized, hadn't been built as a commercial proposition, but as a sort of stunt: the link which connected, at last, all of the System's planets to the rapid-transit hub at Jupiter.

She tired of her plodding survey. She made sure she could locate the crash scar, lifted the scooter to a mile above the surface, and flew towards the south polar cap.

Cobh called from the Interface. "I think I'm figuring out what happened here -- that superluminal effect I talked about. Lvov, have you heard of an Alcubierre wave?" She dumped images to Lvov's desk -- portraits of the wormhole Interface, various graphics.

"No." Lvov ignored the input and concentrated on flying the scooter. "Cobh, why should a wormhole become unstable? Hundreds of wormhole rapid transits are made every day, all across the System."

"A wormhole is a flaw in space. It's inherently unstable anyway. The throat and mouths are kept open by active feedback loops involving threads of exotic matter. That's matter with a negative energy density, a sort of antigravity which--"

"But this wormhole went wrong."

"Maybe the tuning wasn't perfect. The presence of the flitter's mass in the throat was enough to send the wormhole over the edge. If the wormhole had been more heavily used, the instability might have been detected earlier, and fixed..."

Over the gray-white pole, Lvov flew through banks of aerosol mist; Cobh's voice whispered to her, remote, without meaning.

Sunrise on Pluto:

Sol was a point of light, low on Lvov's unfolding horizon, wreathed in the complex strata of a cirrus cloud. The Sun was a thousand times fainter than from Earth, but brighter than any planet in Earth's sky.

The inner System was a puddle of light around Sol, an oblique disc small enough for Lvov to cover with the palm of her hand. It was a disc that contained almost all of man's hundreds of billions. Sol brought no heat to her raised hand, but she saw faint shadows, cast by the Sun on her face plate.

The nitrogen atmosphere was dynamic. At perihelion -- the closest approach to Sol, which Pluto was nearing -- the air expanded, to three planetary diameters. Methane and other volatiles joined the thickening air, sublimating from the planet's surface. Then, when Pluto turned away from Sol and sailed into its two-hundred-year winter, the air snowed down.

Lvov wished she had her atmospheric-analysis equipment now; she felt its lack like an ache.

She passed over spectacular features: Buie Crater, Tombaugh Plateau, the Lowell Range. She recorded them all, walked on them.

After a while her world, of Earth and information and work, seemed remote, a glittering abstraction. Pluto was like a complex, blind fish, drifting around its two-century orbit, gradually interfacing with her. Changing her, she suspected.

Ten hours after leaving the crash scar, Lvov arrived at the sub-Charon point, called Christy. She kept the scooter hovering, puffs of gas holding her against Pluto's gentle gravity.