In The Time of Dinosaurs

"It's a comet," Cassie said. "Isn't it absolutely beautiful?"
"Yeah. Looks awfully close." I gazed up at the sweep of bright dust trailing from the brilliant head.
<It is. In the last three hours it has grown noticeably larger.>
I glanced over at Ax. He was outlined against the stars, a dark shadow with stalk eyes turning restlessly. "It's not going to hit us or anything, is it?" I laughed when I said it.
<I don't think so. First of all, the odds against any particular comet hitting a particular planet are very large. Millions to one at the very least.
Especially since Earth is not large enough to exert much of a gravitational pull. Besides, the comet is now so close and moving so quickly, I have been able to keep track of a rough trajectory. It will be very close. No more than one or two diameters of Earth, perhaps. But I believe it will miss.>