Winter World (The Long Winter #1)(22)

“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.”