Firstborn

“I wish you wouldn’t call them that,” Cassie murmured. She leaned forward to see. “It looks like another asteroid,” she said. “A rock with a silver net around it.”

That was pretty much what the tractor was: a minor asteroid, much smaller than the flying-mountain cannonball. The rock had had a net of tough nanotube rope cast around it, and an antimatter-drive engine was fixed to its surface. “We used one of the early prototype engines from the Trojan shipyards. Not human-rated but it’s pretty reliable.”

Cassie began to see it. “You’re using this to steer the bigger asteroid, the cannonball.”

“Yes — with gravity. It turns out to be surprisingly hard to deflect an asteroid…”

Turning aside the path of an asteroid had been studied for a century or more, since it had become understood that some asteroids crossed the path of the Earth, and, at statistically predictable intervals, collided with the planet.

A dangerous rock was generally too big to destroy. An obvious idea was to knock it aside, perhaps with nuclear weapons. Or you could attach a drive to it and just push it. Or you could attach a solar sail to it, or even paint it silver or wrap it in foil, so the pressure of sunlight pushed it aside. Such methods would deliver only a small acceleration, but if you could catch the rock early enough you might do just enough to keep the rock from hitting its undesired target.

As the asteroid belt was gradually colonized, all these methods had been tried; all failed, to varying degrees. The trouble was that many larger asteroids weren’t solid bodies at all, but swarms of smaller rocks, only loosely bound by gravity — and they were generally rotating too. Try to push them, or blow them up, and they would just fragment into a cloud of smaller impactors that would be almost as lethal and all but impossible to deal with.

So the idea of the gravitational tractor was developed. Position another rock near your big problem asteroid. Push the second rock aside, gently. And its gravity field would tug at its larger sibling.

“You see the idea,” Bella said. “You have to keep pushing your rock just too feebly to be able to escape the asteroid’s gravity field, so your tractor remains bound to the target. And the target will be drawn away no matter how broken-up it is. The only tricky part is orienting your tractor’s exhaust plume so it doesn’t impact the target’s surface.”

Cassie nodded, a little impatiently. “I get the idea. You’re deflecting the orbit of this rock, this cannonball —”

“So that it hits the Q-bomb. The bomb and the cannonball are on radically different trajectories; the impact will be fast—

high-energy.”

“When will this happen?”

“In fact,” Thales said gently, “it did happen, nearly half an hour ago. Two minutes until the report comes in, Bella.”

The graphics of tractor and cannonball vanished, to be replaced by a steady image of the Q-bomb, that eerie sphere visible only by reflected starlight, floating in a cloud of velvet above Bella’s desk.

And beside it was a matchstick spacecraft.

Cassie understood. It took her a few seconds to compose herself. Then, wide-eyed, she said, “It’s happening now. This impact.

And your daughter is out there, in her shrouded battleship, observing. You brought me in at a time like this?”

Bella found her voice was tight. “Well, I need to keep busy.

And besides — I think I needed to see your reaction.”

“Thirty seconds, Bella.”

“Thank you, Thales. You see, Cassie—”

“No. Don’t say any more.” Impulsively Cassie leaned across the table and grabbed Bella’s hand. Bella hung onto it hard.

In the graphic, bomb and escort hung silently in space, like ornaments.

Something came flying into the desktop image from the left-hand side. Just a blur, a gray-white streak, too fast to make out any details. The impact brought a flash that filled the virtual tank with light.

Then the projection fritzed and disappeared.

Bella’s desk delivered scrolling status reports and talking heads, all reporting aspects of the impact. And there were calls from across Earth and the Spacer colonies, demanding to know what was going on in the belt; the explosion had been bright enough to be seen with the naked eye in the night skies of Earth, as well as across much of the rest of the system.

By pointing, Bella picked out two heads: Edna, and then Bob Paxton.

“… Just to repeat, Mum, I’m fine, the ship’s fine, we stood off sufficiently to evade the debris field. Quite a sight, all that white-hot rock flying off on dead straight lines! We got good data. It looks as if Lyla’s projections on the likely loss of mass-energy by the Q-bomb have been borne out. But—”

Bella flicked to Bob Paxton; his face ballooned before her, ruddy, angry. “Madam Chair, we haven’t touched the damn thing.

Oh, we bled off a bit of mass-energy, even the Q couldn’t eat a fucking asteroid without burping, but not enough to make a bit of difference when that thing gets to Earth. And get here it will. It’s not been deflected at all, not a hairsbreadth. It defies everything we know about inertia and momentum.

“And — okay, here it comes. We got the numbers now to do some extrapolating about what happens to the Earth if the Q-bomb hits, on the basis of how the rocks we have been throwing seemed to have drained the bomb. Umm. The bomb is not infinite. But it’s big. The bomb is big enough to destroy Mars, say. It won’t shatter Earth. But it will deliver about as large an impact as the planet could sustain without breaking up. It will leave us with a crater the size of Earth’s own radius.” He read, “ ‘This will be the most devastating event since the mantle-stripping impact that led to the formation of the Moon…’ ” He ran down, and just stared at the numbers off camera. “I guess that’s that, Madam Chair. We did our best.”

Bella had Thales hush his voice. “Well, there you are, Cassie. Now you know everything. You’ve seen everything.”

Cassie thought it over. “I’m glad your daughter is okay.”

“Thank you. But the strike failed.” She spread her hands. “So what do you think I should do now?”

Cassie considered. “Everybody saw that collision, on Earth and beyond it. They know something just happened. The question is, what do you tell them?”

“The truth? That the world is going to end by Christmas Day?” She laughed, and wasn’t sure why. “Bob Paxton would say, what about panic?”

“People have faced tough times before,” Cassie said. “Generally they come through.”

“Mass hysteria is a recognized phenomenon, Cassie. Documented since the Middle Ages, when you have severe social trauma, and a breakdown of trust in governments. It’s a significant part of my job to ensure that doesn’t happen. And you’ve already told me the governments I work for aren’t trusted.”

“Okay. You know your job. But people will have preparations to make. Family. If they know. ”

Of course that was true. Looking at Cassie’s set, determined face, the face of a woman with children of her own under threat, Bella thought she could use this woman at her side in the days and weeks to come. A voice of sanity, amid the ranting and the angry.

And somebody was ranting at her right now. She glanced down to see the choleric face of Bob Paxton, yelling to get her attention.

Reluctantly she turned up the volume.

“We got one option left, Chair. Maybe we ought to exhaust that, before we start handing out the suicide pills.”

“Bisesa Dutt.”

“We’ve been pussyfooting around with these fuckers on Mars.

Now we got to go get that woman out of there and into a secure unit. Earth’s future clearly depends on it. Because believe me, Chair Fingal, we ain’t got nothing else.” He paused, panting hard.

Cassie murmured, “I’m not sure what he’s talking about. But if there is another option—” She took a breath. “I can’t believe I’m saying this. I guess this isn’t like the sunstorm, when we all had to