At 150,000 feet, Mercer should have been cooking.
The altimeter read 28.4 miles. The atmosphere outside was so thin it barely qualified as atmosphere—more like the ghost of air, the philosophical concept of air, air that had given up on being air and decided to pursue other interests. The reaction thrusters had stopped even pretending to work. The rocket climbed on main engine thrust alone, a controlled explosion pushing against the memory of resistance.
Through the viewport, stars were visible even though the sun was still up. Not the sun as seen from ground level—this sun was different. Harsher. More focused. Like a spotlight rather than a diffuse glow, its light cutting through the non-atmosphere with laser precision. The sky wasn’t blue anymore. It was black, pure black, the kind of black that made you understand why ancient peoples had been terrified of the void.
Mercer checked his instruments out of habit, the way a pilot does, the way he’d been trained to do since flight school.
Altitude: 151,000 feet.
Velocity: Mach 4.2 and climbing.
Fuel: 31% and dropping faster than he’d like.
External temperature: -67°F.
Mercer stared at that last reading.
Then he checked it again.
-67°F.
Negative sixty-seven degrees Fahrenheit.
He was in the thermosphere. The official thermosphere, the one that every textbook and every FASE document and every atmospheric science paper said reached temperatures of 2,500 degrees Fahrenheit. Sometimes higher during solar activity. Hot enough to melt steel. Hot enough to vaporize aluminum. Hot enough to turn a spacecraft into a very expensive shooting star.
His external temperature probe—the one specifically designed to measure atmospheric temperature at extreme altitudes—was reading negative sixty-seven degrees.
And dropping.
Mercer watched the number tick down. -68°F. -69°F. -70°F.
“Well,” he said to the empty capsule, “that’s not right.”
The understatement of the century, possibly. The understatement of all centuries.
He was supposed to be in an inferno. The thermosphere was supposed to be the hottest part of Earth’s atmosphere, where solar radiation heated the sparse gas molecules to temperatures that would make the surface of the sun feel like a pleasant spring day. This was the layer where meteors burned up, where the aurora borealis danced, where the very concept of “temperature” became academic because there were so few molecules to actually transfer heat.
Except his temperature probe was reading -71°F and still dropping.
Mercer increased thrust slightly, climbing faster. The temperature kept falling. -73°F. -75°F. -76°F.
The OSS orbited at 250 miles up—right in the heart of the thermosphere. Spacewalks happened there regularly, astronauts floating outside in suits designed to protect against vacuum and radiation. But not against 2,500-degree temperatures. Solar panels. Aluminum structures. Camera lenses. All of it supposedly functioning perfectly in an environment that should have melted them into slag.
Unless the thermosphere wasn’t actually 2,500 degrees.
Unless the entire temperature model was wrong.
And suddenly he was back in Sarah’s apartment, two months ago, laptop open between them, staring at a graph that made no sense.
“I need you to look at something,” Mercer had said, pulling up an atmospheric temperature chart on his laptop. The kind of chart you’d find in any meteorology textbook, any atmospheric science course. Official. Accepted. Unquestioned.
Sarah leaned in, studying it. The graph showed temperature on one axis, altitude on the other. At ground level: normal temperatures, 60–70°F. As you climbed, the temperature dropped—the troposphere getting colder with altitude, exactly as anyone who’d ever been on a mountain could confirm.
Then, at about 30,000 feet, the temperature started rising again. The stratosphere, warming as you climbed, thanks to the ozone layer absorbing UV radiation.
Then it dropped again in the mesosphere.
And then, at about 50 miles up, the graph did something absolutely insane.
It shot upward. Vertical. The temperature line went from -130°F to 2,500°F in the span of a few miles. The thermosphere, they called it. The hot layer. The inferno at the edge of space.
“2,500 degrees,” Mercer said, tapping the screen. “That’s hotter than a blast furnace.”
Sarah frowned. “During solar storms, it can reach 4,500 degrees.”
“And the OSS orbits in this layer.”
“At 250 miles up.” She paused, following his logic. “Right in the middle of it.”
Mercer pulled up images of the OSS. The solar panels, gleaming and pristine. The aluminum modules, unmarked and undamaged. The cameras and instruments and delicate equipment, all functioning perfectly in what was supposedly a 2,500-degree environment.
“How?” he asked simply.
Sarah pulled the laptop closer, scrolling through technical documents. “The official explanation is that temperature in the thermosphere doesn’t work the way we think it does. The molecules are so sparse that even though they’re moving very fast—which is what we measure as temperature—there aren’t enough of them to actually transfer heat effectively.”
“So it’s 2,500 degrees, but it doesn’t feel like 2,500 degrees.”
“That’s what they say.”
“Because there’s no conduction or convection, only radiation.”
“Right.”
Mercer leaned back, thinking. “Okay. But radiation still works. The sun heats things by radiation. That’s how solar panels work. That’s how anything in space gets heated.”
“Yes,” Sarah said slowly, seeing where he was going.
“So even if there’s no air to conduct heat, the solar radiation alone should be cooking everything up there.”
Sarah nodded, pulling up more data. “The moon’s surface reaches 260 degrees Fahrenheit in direct sunlight. And that’s with no atmosphere at all, just direct solar radiation.”
“So the OSS, in direct sunlight, in the thermosphere, with molecules that are supposedly 2,500 degrees...”
“Should be melting,” Sarah finished.
“But it’s not.”
“No.”
They sat in silence for a moment.
“Show me the spacewalk footage,” Mercer said.
Sarah pulled up video of astronauts floating outside the OSS. The suits were impressive—white and bulky, designed to protect against vacuum and radiation. But they weren’t heat suits. They weren’t designed for 2,500-degree environments. They had cooling systems, yes, but those were for the astronaut’s body heat and the heat from direct sunlight, not for surviving in an inferno.
“Those suits,” Mercer said, “are designed to handle maybe 250 degrees of solar heating. Maybe. They’re not designed for 2,500 degrees.”
Sarah was already pulling up the technical specifications. “No. The EMU—the spacesuit—has a cooling system rated for about 250 degrees of thermal load. That’s it.”
“So either the thermosphere isn’t actually 2,500 degrees...”
“Or nothing is actually up there,” Sarah said quietly.
Mercer pulled up more images. Satellites with delicate instruments. Solar panels with exposed circuitry. Telescopes with precision optics. All supposedly functioning in the thermosphere, all supposedly surviving temperatures that would melt steel.
“The math doesn’t work,” he said. “Either the temperatures are lies, or the satellites are lies, or both.”
Sarah stared at the graph again, then looked at him. “What if they’re measuring something else entirely?”
“Like what?”
“You said it yourself—a ceiling,” Sarah said, her voice gaining momentum. “What if they’re measuring the temperature of the firmament itself? The solid barrier. They take readings, they detect something, and they call it the thermosphere. They say it’s hot gas. But maybe it’s just... the dome. The boundary. And they’re measuring its surface temperature.”
Mercer leaned forward. “If you’re right, if there’s a solid dome up there, and they’re measuring its temperature and calling it atmospheric temperature...”
“Then the readings would change as you got closer to it,” Sarah finished. “You wouldn’t be measuring sparse hot gas. You’d be measuring the actual surface of something solid. And solid things have real temperatures. Measurable temperatures. Temperatures that make sense.”
“What temperature would a dome be at that altitude?”
Sarah grabbed her phone, started calculating. “Depends on the material, the sun exposure, the thermal properties. But if it’s in shadow, or if it has high thermal mass, or if it’s designed to regulate temperature...” She looked up at him. “It could be cold. Very cold. Space is cold. If the dome is the boundary between the world and whatever’s beyond, it might be freezing.”
Mercer felt the pieces clicking into place. “So if I flew up there, and my temperature probe showed dropping temperatures instead of rising ones...”
“Then you’d know,” Sarah said. “You’d know the thermosphere is a lie. You’d know there’s something solid up there. You’d know they’ve been measuring the dome and calling it atmosphere for decades.”
“And I’d know how close I was getting to it.”
Sarah looked at him for a long moment. “You’re really going to do this.”
“We’re really going to do this,” Mercer corrected.
She nodded slowly. “Then we need to design a temperature probe that can handle extreme readings in both directions. If you’re right, the temperature gradient near the dome could be steep.”
“Can you source the components?”
“I can source anything,” Sarah said. “That’s what I do.”
The temperature gauge read -82°F.
Mercer was at 156,000 feet now. Twenty-nine and a half miles up. Deep in what should be the hottest part of Earth’s atmosphere.
And it was colder than Antarctica.
He watched the gauge drop. -83°F. -85°F. -87°F.
The thermosphere wasn’t hot gas. It never had been. They’d been measuring something else—something solid, something real, something with actual thermal properties that made sense. They’d been measuring the dome.
And he was getting close to it now.
Through the viewport, the blackness above seemed different somehow. Not quite visible, not quite tangible, but present. Like looking at a wall in a dark room—you couldn’t see it, but you knew it was there. The stars burned with that same steady, unblinking intensity, and Mercer realized with a start that they looked closer. Not metaphorically closer. Actually closer. Like lights on a ceiling that was approaching.
Or that he was approaching.
The radiation monitor was still beeping. The temperature gauge was still dropping. The altimeter was still climbing.
-91°F.
158,000 feet.
Thirty miles up.
Somewhere above him, maybe thirty miles, maybe less, there was a boundary. A ceiling. A firmament. Something solid enough to have a temperature, something real enough to generate an electromagnetic field, something close enough that his instruments were detecting it with increasing urgency.
Something they’d been lying about forever.
Mercer checked his fuel. 27%. Enough to get him higher. Enough to reach the boundary.
Maybe not enough to get back down, but that had never really been the plan anyway.
He increased thrust.
The rocket climbed through the freezing thermosphere that wasn’t supposed to be freezing, toward the dome that wasn’t supposed to exist, toward the truth that everyone had been trained not to see.
The temperature kept dropping.
The radiation kept beeping.
And through the viewport, in the blackness above, something was becoming almost visible.
A boundary.
A ceiling.
The edge of the world.
Mercer climbed toward it.
The Snowglobe
This is a work of fiction. Names, characters, places, and incidents are either products of the author’s imagination or are used fictitiously. Any resemblance to actual persons, living or dead, events, or locales is entirely coincidental. This narrative is presented as allegory and entertainment, not as factual representation of scientific, historical, or theological claims.