So it would be easy for the arklets to get clear of the thickening atmosphere by abandoning Izzy, at least for the time being, and jumping to higher orbit. Their drag problems would be solved. But in so doing they would lose the ability to shelter behind Amalthea and begin to take damage from bolides. Exactly how much damage depended on how thick and fast the rocks were coming in, and what the distribution of sizes was—another one of those questions of colossal import that couldn’t be answered until the Hard Rain had actually started and data had been gathered.
And, so far, the data were too thin to make any real determination. With a few spectacular exceptions, bolide impacts and casualties had been light. But this didn’t mean it would remain thus. The White Sky was an ever-changing phenomenon. The explosive uptick in the Bolide Fragmentation Rate that had signaled its onset was still ongoing. The distribution of rock sizes and orbital parameters would continue changing for thousands of years. Trends could be observed, and predictions could be made, but beyond a certain point it was guesswork.
At any rate, Markus had rolled the dice on the gambit that they were now executing. If it worked, and they could slow Ymir down enough to mate her with Izzy, then the Big Ride strategy became possible, and the arklets could climb to higher and safer altitudes behind the shelter of Amalthea’s metal and Ymir’s ice.
The one part of that plan that Markus apparently had not considered until now was that the atmosphere was too big.
In truth, it wouldn’t have made a difference if he had considered it. The crucial decision had been made and executed weeks ago by Sean Probst, when he had laid in a course at L1 and executed the burn that had placed Ymir on its current trajectory. This was an ellipse with a very low perigee. That was a sound idea from an orbital mechanics point of view in that the steam engine would have maximum leverage at that point—it was the natural place to make a burn and effect a transition to a low circular orbit matching Izzy’s. But, sick and exhausted from his two-year odyssey, isolated from the latest scientific discourse by radio failure, Sean might have overlooked the expansion of the atmosphere when making his calculations.
“Are we going in?” Vyacheslav asked. This being a polite euphemism for the scenario where Ymir got so deep, and slowed down so much, that it burned up and became just another streak of blue light against the lambent background of the pyrosphere.
“We are more likely to skip, I think,” Markus said. Meaning that Ymir might bounce off the atmosphere like a flat rock skimming across a pond. “With unpredictable results. But I cannot be sure. All I am saying is that this is not going to be the mission plan that Sean had in his mind. It is going to be something else. Something maybe a little more exciting.”