Lin Yuan’s rover crunched over the scree at the edge of Tycho Crater, kicking up plumes of lunar dust that hung suspended in the vacuum like silver ghosts before settling back onto the gray regolith. The heads-up display in his helmet read 0300 hours Earth Standard Time, but on the far side of the Moon, time was meaningless. There was only the eternal ink-black sky and the faint blue arc on the distant horizon—Earth, locked in place by tidal forces, glowing like a marble wrapped in gossamer.
“Tianyan, confirm signal source coordinates,” he said, his voice muffled inside the helmet.
“Coordinates synced to nav screen. Caution: Terrain gradient ahead exceeds fifteen degrees. Recommend deceleration.” The AI’s mechanical female voice was devoid of emotion, yet it brought Lin Yuan an odd sense of comfort. He gripped the control stick, guiding the rover’s six sets of tracks to slowly embed into the lunar soil as it rolled over a chunk of basalt half-buried in the dust. The rock’s surface was pocked with honeycomb pores, as if pierced by countless needles, glinting with a cold metallic sheen under the rover’s searchlights.
The signal source was three hundred meters underground. As Lin Yuan rappelled down the entrance of the lava tube, the crystals on the rock walls suddenly lit up. At first, they were scattered blue lights, like fireflies on a summer night, then they connected into a glowing river that wound its way down the tube, as if someone had laid a starlit path beneath the surface. He reached out to touch the nearest crystal, and a bone-chilling cold shot up his finger. The surface of the crystal rippled at his touch, like a reflection on water disturbed by a breeze.
“Tianyan, analyze crystal composition.” His breath condensed into a fog inside the helmet.
“Unknown silicon-based compound. Structure similar to quartz on Earth, but molecular arrangement exhibits aperiodic order.” The AI paused. “Warning: Abnormal vibration detected. Frequency matches signal source.”
Before he could react, a violent tremor shook the ground beneath him. Lin Yuan looked up to see the roof of the lava tube cracking, with rocks raining down like hail. He yanked the rope tight, pressing his body against the rock wall as he slid down, the soles of his boots screeching against the crystals. When the last boulder crashed onto the spot where he had been standing, the comm crackled with static before falling into complete silence.
Oxygen levels at forty percent. Lin Yuan switched on the searchlight on his helmet, the beam piercing the darkness to illuminate the passage ahead. The crystals on the walls grew denser, some hanging like stalactites, others clustering like coral, refracting rainbow halos under the light. He suddenly noticed that the arrangement of the crystals was not random—they formed complex geometric patterns, like a giant star chart or an unknown script.
A faint sound of water echoed from the end of the passage. Lin Yuan quickened his pace, turning a corner, and the sight before him made him hold his breath.
It was a massive underground cavern, at least a hundred meters in diameter. In the center lay a calm lake, its water so clear that the rocks at the bottom were visible. The surface reflected the crystal dome above, as if the entire starry sky had been trapped inside. On the rock walls around the lake grew semi-transparent creatures. They resembled giant jellyfish, their bodies composed of countless tiny crystals, their tentacle-like appendages swaying gently. Each sway made the surrounding crystals emit a soft hum.
Lin Yuan’s heart pounded. He slowly approached the lake, seeing the “eyes” of the jellyfish-like creatures—if they could be called eyes—two glowing spheres that stared at him quietly. He thought of deep-sea creatures on Earth, those life forms that live in darkness, communicating with light and sensing the world through vibrations.
“What… are you?” he whispered, his voice echoing in the cavern.
The creatures did not answer, but the surrounding crystals suddenly began to flash, their frequency accelerating like a heartbeat. Lin Yuan instinctively touched the geological hammer at his waist, the tool he used to break rocks during exploration. He suddenly remembered the frequency of the signal source—a regular vibration every three seconds, like a call.
He raised the hammer and tapped lightly on the rock wall.
“Dong.”
The sound spread through the cavern, and the flashing frequency of the crystals suddenly changed, from a rapid “dong dong dong” to a slow “dong—dong—”. The jellyfish-like creatures’ tentacles swayed faster, their bodies beginning to glow, the light shifting from pale blue to warm orange, like the sea at sunset.
Lin Yuan tapped again, this time mimicking their frequency, with a three-second interval.
“Dong… dong…”
The crystal dome suddenly lit up, and countless light points flew up from the rock walls, swirling around Lin Yuan like fireflies. He saw images appear among the light points: a giant asteroid撞击 the Moon, magma erupting to form this lava tube; then long years passed, crystals growing slowly underground, jellyfish-like creatures evolving in the lake, recording history with vibrations and transmitting memories with light.
They were not monsters, but carriers of the Moon’s memory.
The comm suddenly crackled to life, and Lao Zhang’s voice came through: “Lin Yuan! Are you still alive? We detected your signal!”
Lin Yuan looked up to see a crack in the cavern roof, with searchlight beams from the rescue team shining through. He shouted into the comm: “I’m okay! Don’t blast this place! They mean no harm!”
The jellyfish-like creatures seemed to understand his words. Their tentacles swayed gently, and the light gradually dimmed. The light points on the crystal dome slowly fell back onto the rock walls, returning to their original calm. Lin Yuan walked to the lake, picked up a crystal, and it warmed slightly in his palm, like a beating heart.
When he returned to the base, the arc of Earth was rising from the horizon. Lin Yuan stood on the observation deck, looking at the blue planet, thinking of the star chart in the underground cavern. The Moon had always been protecting Earth, with its silence, its memories, and the life forms that lived in the darkness.
He placed the crystal on the windowsill, where it glowed with a soft blue light under the moonlight, like a star from the Moon.
“Tianyan,” he said, “send a message to Earth. Tell them there is life on the far side of the Moon.”
“Message sent.” The AI paused. “Additionally, the crystal is emitting a weak signal. Frequency matches the signal source.”
Lin Yuan smiled. He knew it was not a signal, but an echo from the Moon.