"I'm sorry, could you repeat the question?" Dr. Taylor was not accustomed to being stumped. Rarely had it happened during his time earning an astrophysics PhD, and it happened even less in his current position: principal investigator for NASA's most advanced planet hunter yet.

But here he was, stalling for time, because a 10th grader had asked a questioned that he had simply never considered.

The young woman snapped her gum and repeated, "Is it bad. 'Stealing momentum' from our planets?"

"Well, no, the satellite is so small, relatively speaking, that the slingshot maneuver has an imperceptibly small affect on the planet."

"But it slows it down right? The planet."

"Technically yes, but it is a very small amount."

Another student who, unlike most at this point, had been following with interest, pitched it, "And you said in space that slowing down is like falling."

"That is correct, as an orbiting body, a satellite, slows, its orbit will become lower at the opposing point until the perigee intersects with the body being..."

"Right," a third student in the back row broke in, "and the Earth orbits the sun. So when you slingshot to speed up your satellite, you are making us fall into the sun. At least a little."

Taylor looked to the teacher; she seemed to be thoroughly enjoying her students having a different target to pillory with questions for a change. "Their logic seems on point Dr. Taylor."

He collected himself, took a depth breath, and re-framed the question. It was a good one, but the students where missing the scale of it all.

"Okay, so imagine I'm Lex Luthor..."

"Who?"

"A bad guy. Superhero movie villain, right?"

A few nods.

"And my plan is to plunge the Earth into the Sun by launching rockets and using slingshot maneuvers to slow the Earth's orbit. I would need to figure out just how many rockets to launch with how big of payloads and how fast to accelerate the payloads and so on, right?

Don't worry, I'm not going to make you do the math. But you get what I'm saying, right? You could figure it all out." Taylor got a few nods from his inquisitors. "Right, so here's the thing: the Earth is so massive that I would need to launch all of Texas before our year lost a second. Roughly."

He got a few nods, but most the students seemed to be staring at certain spot behind Taylor's head and he had a sneaking suspicion that there was a clock there. At least the idea seemed to get through to them, he thought, and the most difficult talk of his life was almost over.

"All right class," the teacher rose, "lets give a big thank you to Dr. Taylor for comming in today."

As if on cue the bell range and Taylor got a few muffled thanks as the students began filing out. He saw one student hanging back a bit to ask a question. Taylor started sorting through what the kid might want, career advice, a follow question?

"Hey Doc," the kid brushed his long hair out of his eyes, "at least you figured out how to get rid of Texas, huh?"

"Soooo, how was the talk?"

"It was fine. I don't want to talk about it. What's up?" It wasn't like Colleen to send text messages, and leave a voicemail, and to call. Surely it wasn't just to rib him about the high school talk. Colleen, also an astrophysics PhD and deputy on the project, could empathize with just how much Taylor disliked public speaking because she was the only one on the team who disliked it more.

"Well, we've been going over the latest data from atlantis system."

"That's the second round of observations there, right."

"Yup. And. Well, things aren't lining up." Colleen feel silent.

"Aren't lining up? How?"

"Some of the orbital periods are off."

The Shields spacecraft, named after the early exoplanet research Aomawa Shields, was able to detect planets in the same way as early planet hunters like Kepler: by recording the slight dimming of a star as a planet transited between it and our solar system many light years away. If Shields hadn't run through the mathmatics of the telescope himself several times he wouldn't actually believe that such a slight dimming of a distant star could be measured. And the results where hard to argure with: hundreds of thousands of planets had been discovered this way.

Shields was an evolution of this technology: it improved upon previous attempts by using a massive star shade to obscure all light from the surronding stars. The shade was a second spacecraft unto itself which had to keep it's position in precise alignment with the main telescope of Shields.

This is all exposition for the main store: Taylor's team spots a planet that seems to have recently had a major shortening of its orbital period. They figure out that the only realistic explanation is that the planet is being used for MASSIVE slingshot maneuvers. The rest is just figuring out what that could mean (like a mass migration or invasion)...