Moonfall

PROBABLE COMET. VERY LARGE HALO.

A comet.

Tory was delighted. It was always exciting to be in on a discovery like this, even if credit would go to Tomiko What's-her-name in St. Louis. But if it was a comet, it would orbit the Sun and go back out the way it had come. Which meant it might not be visible to the naked eye for several months, until Earth had traveled to the other side of its orbit.

But that raised a question: Why had no one noticed it, say, last October, when it was on its way in and Earth was on the far side of the Sun?

"Ready," she told Windy.

"Do it."

She'd already entered the comet's coordinates and had only to activate. This she did with a flourish, and she and her supervisor watched the monitors blank out. The orbiter would need several minutes to shift on its axis, realign, and focus.

"It's probably because it isn't very bright," said Windy. "Happens all the time."

"All the time?"

"Well, occasionally."

Images started to come in. The definition adjusted, and they saw it! "Comet Tomiko," said Tory.

Windy grinned. "Stay with it," he said. "Eventually you'll get one of your own."

She increased magnification. "Not much of a tail." It was gauzy. Barely perceptible.

Windy shook his head. "I wonder if we've seen it before."

Tory called up the register for regularly recurring comets and initiated a search.

"Negative," she said after a time. "We don't know this one."