Her finger hovered, shaking. Giovanni gently took her hand in his and pressed down.
The Earth and planets set back into motion, at one second per week of simulated time. Mercury was catapulted outward, Venus dragged away from the Sun violently as well, with Mars being pulled toward it. The Sun itself was dragged along behind Nomad, until Nomad sped away into space and released it. Saturn was dragged backward, into a retrograde orbit, circling behind the Sun. Just like Jess’s other simulation.
And the Earth…
Nomad pulled the Sun, but it also pulled Earth.
While the other planets were tossed around randomly, the Earth continued to orbit the Sun. Jess watched the climate simulation: the temperature dropped from 14.8 Celsius, to 14.4 and then 13.8…but then it climbed, back to 14.2. The Earth completed a full circuit around the Sun. Slightly elliptic, but well within the green-highlighted habitable zone. Jess stopped the simulation.
“Hey, what are you doing?” Giovanni was entranced.
“Running it again.” She hit the reset button, watched Nomad tear through the solar system, the planets scattering. But not the Earth. It lazily circled the sun as if nothing had happened.
How was it possible?
A mass forty times the Sun, passing half the distance from the Sun to the Earth, and the Earth remained in an almost stable orbit? Jess traced her finger along the path of Nomad, stared at the Sun and Earth, her face erupting in a smile. She laughed, clapping her hands together. “Yes, yes!” she cried.
Giovanni stared at her as if she were mad, but her smile was infectious. He grinned. “What does it mean?”
“It’s all in the geometry of the encounter,” Jess explained, pointing at the laptop. “The center of mass of Nomad passed almost in the solar plane, and passed the Earth and Sun at almost exactly the same distance, like a speeding bullet.” She took a deep breath. “Have you ever seen that video, where one of the Apollo astronauts, standing on the moon, drops a hammer and a feather side by side?”
Giovanni shook his head.
“The hammer and feather fall at exactly the same speed, they hit the ground at the same time. Same experiment that Galileo did from the leaning tower, dropping a pebble and a cannon ball. They both hit the ground at almost the same time. It doesn’t matter what the mass of an object is—a grain of sand or an elephant—if they experience the same gravitational field, they’ll accelerate exactly the same.
“That’s what happened.” Jess pointed at the screen. “All the other planets, Nomad passed at different distances than it passed the Sun, they all experienced a different gravitational acceleration from Nomad.”
“But the Sun and Earth experienced the same gravitational acceleration?” Giovanni asked, still not quite getting it but smiling all the same.
“Exactly!” Jess clapped her hand again. “All the other planets accelerated at different rates, so they were pushed in random directions. But not the Earth. The Sun and Earth were both pulled the same amount in the same direction, even though the sun is three hundred thousand times heavier. Pure luck of geometry. I mean, there’s a lot more going on, but that’s the big brush strokes.”
“So…we’re saved…?” Giovanni said tentatively.
“Look at the simulated global temperatures. Hovering right between 14 and 15 degrees.”
Giovanni pondered this for a second before responding, “Then why is it so cold outside? It should be fifteen Celsius at this time of year. It’s at freezing and dropping.”
Jess ran the simulation again, marveling at it. “That’s the ash and dust thrown up into the atmosphere. Hundreds of volcanic eruptions have covered the Earth in a thick blanket. We’re not getting much heat from the Sun.”
“And the Gulf Stream. I’d bet that’s why Europe is so much colder than anywhere else. Nomad churned up the oceans. Those researchers we talked to in Greenland? Might have pulled off enough of the ice cap to disrupt the Gulf Stream.”
Giovanni tapped his teeth together. “And so?”
“At this rate, Tuscany is going to freeze colder than Antarctica in a few weeks.”
Giovanni rubbed his face, nodding. “Then we need to get south. Most of Africa survived intact. It’s even raining in the Sahara.” He tapped his pile of scribbled notes. “And we have a branch of our family that lives in Tunisia. They have a villa in the Atlas Mountains on the edge of the desert.”
“Have you contacted them?” Jess asked breathlessly. Sheer hopelessness had suddenly transformed into a bright, burning possibility.
“Not yet.” Giovanni shook his head. “And Hector’s parents were in Africa. If they go anywhere, I would guess they would try to reach our family in Tunisia.”
Jess glanced at Hector.
“So we go south?” Giovanni asked.