IN THE BRIEFING ROOM, the crew stops eating. Those flipping through the binders let the pages fall away from their hands. No one speaks. We’re all trying to process this revelation: there’s a second artifact out there.

In the pit below, the staff around Fowler stops typing. All eyes are on him. And, I realize, me. The crew is waiting for me to ask the next question. Then it feels as if it’s just Fowler and me in the room, rapid-firing questions and answers like two brains effortlessly connecting and sharing

data.

“Location?”

“Ten million miles beyond Mars.” “Size? Composition?”

“Believed to be the same as the other artifact. Or vessel, if they are in fact under their own power.”

“Vector? Velocity?” “Unknown.”

“How’d you find it? Probe?” “Ground-based telescope.”

“How?” I realize the answer as soon as I ask, and offer it: “You traced the first artifact’s course—Alpha’s course? You reversed it.”

“Yes.”

“The implication is that both objects share the same launch point.”

“That’s likely. We’re calling the second object Beta, and their assumed origin point Omega.”

Very interesting. There has to be a larger ship out there—at the omega point. Or a base of some kind. My head buzzes with the possibilities. This

just got a lot more complicated. By orders of magnitude.

Lina Vogel, the German computer scientist assigned to the Pax, clears her throat. “I’m sorry, but my knowledge in this field is quite limited. Some context would be helpful.”

Fowler looks up, as if only now remembering there are other people here. “Of course. What would be helpful?”

“Ah, well, could you… describe the distances involved here, for example?”

“Sure.” Fowler grabs a sheet of paper from the lectern. “Imagine this piece of paper is our solar system, with the Sun at its center. The planets and asteroids orbit in the same plane because they formed out of a dust cloud that was in a disc shape due to the conservation of angular momentum.”

Lina squints uncertainly.

“Sorry,” says Fowler, “that’s not germane to the mission. The point is, all the planets go around the Sun in sort of a track or orbit. The orbits are generally circles, but not perfect circles. Some are more irregular than others. And most comets don’t follow the orbital plane. For example, Pluto’s orbit is more like this.”

He holds the sheet in one hand and moves his hand around it, going below and above at an angle to the plane of the paper.

“Think of space like a fabric, a sheet—or page—that all these planets and moons and asteroids and comets are sitting in. The more mass an object has, the more it depresses into the fabric.” He presses a finger into the sheet. “As massive objects weigh down the fabric, they draw objects to them. We call this effect gravity.”

A few chuckles erupt around the room.

“Take our moon, for example. We believe that roughly fifty million years after our solar system formed, a planet the size of Mars slammed into Earth. The moon is what was left over from the collision. Earth has more mass—its diameter is roughly three and two-thirds the size of the moon, and it’s about twice as dense. The result is that the Earth has a lot more mass—eighty-one times more in fact. The moon’s lower mass is what causes the weaker gravity on its surface, because its mass exerts less pull on other objects.”

Fowler motions for one of his assistants to hold the page for him.

“So the planets orbit the Sun—because it’s the most massive thing in the solar system. Easily. In fact, almost 99.9% of all mass in the solar system lies in our sun. It’s 109 times the diameter of Earth—864,400 miles across. And its mass keeps all the planets in line, orbiting in a plane.” He presses a finger into the page. “And here’s Earth, with its mass. It can’t escape the Sun’s gravity because, well, the Sun weighs about 333,000 times as much as Earth. We’re not going anywhere. But we’ve got enough mass to keep the moon in line.”

He presses another finger into the page. “So the moon is in Earth’s gravity well. And it’s not going anywhere any time soon. This becomes important because you have to think of the planet’s gravity wells like hills that an object has to climb to escape.”

Fowler points to Grigory and Min and the other aeronautical engineer and navigator. “When we talk about distances and, in the binder, where you see the Alpha artifact’s location relative to planetary orbits, these folks are thinking about these things because they have a huge impact on the amount of energy and velocity we need. That is, how much engine power and fuel required.”

He presses a finger deeper into the page. “Because Earth has more mass and stronger gravity, it takes a lot more energy to achieve escape velocity here than it does on the moon. We mitigate the energy requirements in a few ways; namely, by achieving low Earth orbit and then using orbital velocity to help slingshot the object out of the gravity well.”

Fowler inhales. “For the sake of example, here’s how we would travel to Mars. We’d time the launch so that our ships could climb out of Earth’s gravity well in stages. Think of it, again, as climbing a hill. We get out of the atmosphere and use Earth’s orbital velocity around the Sun to slingshot toward Mars. Most of the way, we’re still under the influence of Earth’s gravity. It’s pulling us back, but we’re expending energy to pull away. It takes less energy the farther away we get and the weaker Earth’s gravity gets. At some point, we reach the top of the hill—a place in space where Earth’s gravitational pull on our ship is equal to Martian gravitational pull. Behind us is a hill that leads down to Earth. In front is a hill that leads down to Mars. After that point, the pull of Mars’s gravity is exerting a greater influence on the ship than the pull of Earth’s gravity. We’re going downhill at that point, toward our destination, which impacts fuel and acceleration requirements.”

Fowler looks up at the group. Grigory and Min look bored. Lina is nodding.

“This is all really important because the navigators and engineers have to think about what kind of orbital velocity they’re working with and the gravitational influences on the ship. They have a massive, if you will, impact on the energy required.” The astronomy joke gets a few chuckles, mostly from Fowler’s staff.

“And that leads us back to engines—how much power and how much fuel. Frankly, we’re not sure.”

Fowler points to an assistant. “Could you stand here, please?” To the crew, he says, “This young lady is the Sun.”

She smiles, a bit embarrassed at the attention.

Fowler instructs four more assistants to stand at specific places in the room, which he counts out with steps. “And these fine folks are the planets. The inner planets, anyway—those inside the asteroid belt. And they’re all orbiting the Sun at different speeds and different distances. Mercury is about thirty-six million miles from the Sun. Venus is about thirty million miles beyond Mercury. Earth is roughly twenty-six million miles beyond Venus. And Mars is another fifty million miles away from us—at our closest orbital point.”

Fowler places a stapler between the staffers representing Earth and Venus. “This is Alpha’s location.”

He takes a pen from his pocket and places it a step beyond Mars. “And here’s Beta.

“Our plan has been to use Earth’s orbital velocity to give us a push toward Alpha. And then to use Venus’s gravity to pull us closer.”

Lina cocks her head.

“Keep in mind, the planets are on the same plane, orbiting at different distances—and different speeds. Mercury completes a revolution every 88 days. Venus about every 224 days. Mars takes almost 700 days to orbit the Sun.”

He points to the stapler. “The artifact is orbiting the Sun as well—in a decaying orbit, so it’s spiraling toward the Sun, like a pinball circling a funnel toward the drain.”

Fowler motions toward the young man representing Earth. “The ships will get a push from Earth’s orbital velocity toward Alpha.” He takes a step toward the stapler. “Venus is behind Earth at the moment. But in thirty days,

it will pass Earth. In ten more, it will pass the ships, and seven days later, it will pass Alpha. The ships will use the drag of Venusian gravity to get closer to the artifact.”

Fowler gestures for his team members to return to their seats, and he himself walks back to the lectern. “We’re not certain what kind of orbital velocity we’ll pick up from Earth—because we don’t know if there will be some force applied to the ship modules when they reach low Earth orbit. Will it be a similar solar event that hit the ISS? More powerful? Or nothing? We don’t know. However, we do know precisely when the orbital transfer point will occur between Earth and Venus. Our optimal launch window to reach that transfer point closes in twenty-four hours. If we miss the launch window, it’s unlikely we’ll reach the Alpha artifact. At this point, we don’t have enough data to know whether we could reach the Beta artifact.”

A NASA staffer rushes into the room, a strained look on his face. He pulls Fowler aside and whispers to him. I catch only clips and phrases.

“Debris broke apart.” “Breach.”

“Heat shield compromised.”

He shows Fowler something on a laptop. The NASA director’s eyes go wide. He turns from the man and takes a few steps away, pinching his lower lip. He returns, shaking his head, and speaks quietly, so low I can barely make out the words.

“There’s nothing we can do. At least right now. Just try to keep her alive as long as you can.”