Greg Egan - The Eternal Flame

No one had managed to find so much as a single tiny crater or other blemish left behind by the strange ignitions. With no more empirical clues, three generations of travelers had been left to speculate about the collisions. That the modest spin of the Peerless had been enough to brush the encroaching specks of dust aside ruled out sheer speed of impact as an explanation for the flashes, in favor of some kind of chemical reaction with the rock of the mountain itself. But no theory of chemical luminescence, no theory of fuels and liberators, no theory of light and luxagens, had ever offered a believable account of the events.

Ivo said, “One scrag of calmstone, delivered to the northern gray flats.”

He released the catapult.

Carla glanced across the cabin at Ada, who was resting a hand on the emergency lever that would fire the engines immediately to propel the Gnat out of harm’s way if the Object did a Gemma and began to transform itself into a star. Tamara, clinging to the rope beside Ada, was wearing a heavy blindfold. If the Object burned so fiercely that its radiance became injurious, this macabre precaution might at least spare the sight of one of their navigators.

Carla bent down and peered through the theodolite in front of her—willingly putting one eye at risk in order to cover the opposite contingency, that the flash might be too weak to see any other way—while her fingertips brushed the dials of the adjacent clock. They believed they knew how long it would take the speck of calmstone to reach the surface, but if the reaction itself was delayed the exact timing would be a valuable further datum.

“Opening the shutter,” Ivo said softly.

Carla stared at the starlit gray surface, expecting an anticlimax. The secret that had eluded generations couldn’t give itself up with the first grain of sand they tossed. She felt the dials reach the estimated impact time and move on: one pause beyond, two, three—

A dazzling point of light blossomed against the grayness, like a sunstone lamp seen through a pin-hole. Carla dutifully transcribed the precise time of the event onto her thigh even as she waited for the pin-hole to burst open, for the barrier between the realms to be torn apart and chaos to come spilling through.

The light faded and died. Carla quickly turned around and put an undazzled rear eye to the theodolite. There was no wildfire spreading from the impact site. The surface appeared completely unchanged.

Ivo said, “Tell me I didn’t hallucinate that.”

“Hallucinate what?” Tamara asked impatiently.

“It was bright but… contained,” Carla managed. “Just as they described it in the old fire-watch reports!” Just as Yalda herself had first seen it—looking back on the Peerless from the void, when a construction accident during the building of the spin engines had almost sent her to her death.

Ivo pulled the strip of paper out of the spectrograph. Carla lit a lamp so they could examine it properly. The paper had been darkened across the entire range of frequencies, showing a spectrum similar to that of the light from any burning fuel. But superimposed on this was a feature so sharp that Carla at first mistook it for a calibration mark on the paper—a line Ivo might have drawn for the purpose of alignment. It was no such thing. The paper had been blackened by the flash itself, along a narrow band corresponding to an ultraviolet wavelength of one gross, eight dozen and two piccolo-scants.

Tamara was keeping her blindfold on, so Carla explained the results to her.

“What could produce that?” Tamara asked. “A single, sharp ultraviolet line?”

“I’ve never seen anything like it,” Ivo declared. “No ordinary rock burns with a narrow peak brighter than all the other light from the flame.”

“Let alone just one peak ,” Carla added. “The total amount of energy a luxagen needs to gain in order to escape from calmstone would be something like two dozen times greater than the jump corresponding to that ultraviolet line. You’d expect a liberator for calmstone to modify the energy levels so the total gap was bridged in a lot of small steps—but there’s no reason why all of those steps should turn out to be identical in height!”

Ada said, “And yet, there it is: one lonely peak.”

Ivo launched a second scrag of calmstone, this time at the red-tinged portion of the Object’s southern lobe. The terrain here looked as if it was covered in firestone; watching through the theodolite, Carla braced herself for the sight of a wildfire, if not a full-blown Gemma event.

Three pauses and five flickers after the impact, there was a single, brief pinprick of radiance.

When Ivo extracted the paper from the spectrograph, there were some minor differences across the visible frequencies but the spectrum was dominated by exactly the same ultraviolet peak as before.

Ivo repeated the experiment, choosing two more regions of the Object with their own distinctive appearance. Then he switched the projectile from calmstone to hardstone, then powderstone, clearstone, mirrorstone, firestone and sunstone. In two dozen and four variations, the delay before the flash was sometimes a little longer or shorter, and the visible part of the spectrum showed clear differences that depended on the particular area being targeted on the surface. But in every case, a single ultraviolet line blackened the paper at exactly the same position.

Carla could offer no explanation, and Ivo was equally perplexed. Ivo went so far as to aim the spectrograph at a lamp inside the cabin, to see if the ubiquitous line was really just the product of some bizarre flaw in the optics. It wasn’t.

“Take away the ultraviolet line from this spectrum,” he said, holding up a strip of paper he’d exposed to a flash from the red rock of the southern lobe, “and take away the liberator lines from this one .” He grabbed the test strip he’d made from the lamp. “Apart from those features, they both look the same: burning firestone.”

“So firestone is firestone, luxagen-swapped or not,” Ada said. “Once it’s actually burning, the light is identical, just as Nereo’s theory would predict.”

Carla said, “But the process by which the Object’s firestone is being set alight looks nothing like the way a liberator acts on ordinary firestone. And it’s completely indiscriminate: it acts the same way with every mineral. It doesn’t care about the detailed structure of any of these solids—their geometry, their energy levels. It just does its magic trick and pfft…”

Tamara finally took off her blindfold. “Whether or not we understand the ignition process, surely this is an answer to the fuel problem? Every scrag of the Object can be made to burn! A little too easily for comfort… but if we can slow this thing down enough to keep it in reach, the next generation can deal with the practicalities.”

“Or the next generation could catch up with it and fetch it back,” Ada suggested. “They’ll have had time to think deeply about the results we’ve seen, and work out what’s really going on. We know the Object’s trajectory with very high precision now. We can’t lose track of it.”

Tamara almost seemed swayed, but then Ivo interjected angrily, “We came here to capture the Object! That was the mission the Council approved: to take samples, to do calorimetry, then to trigger a blast that would leave this thing motionless. If we give up now, all we’ll be bequeathing our descendants is a longer journey and a more difficult version of the task we should have done ourselves. We’ve had three generations of theorizing about orthogonal dust, and that’s left us none the wiser. The only way to understand this material is by experiment.”