Much later, after the hole in the roof had been fixed and the debris cleaned up, after the cause of the damage finally had become clear, Frank Ciampi wondered: What are the odds?

He is a doctor. He has worked for 18 years in the two-story building in Lorton that houses the Williamsburg Square Family Practice, in the 9500 block of Richmond Highway. He spends his days walking in and out of examining rooms, seeing patients.

What are the chances, as he goes about his routine, that he'll get hit by a meteorite?

Not impossible.

It almost happened.

"I was in my office doing charts," Ciampi recalled. It was Monday, a little after 5:30 p.m. He was on the building's second floor. "And I heard a loud boom, almost like a small explosion."

At first, he said, he thought a bookcase had toppled nextdoor. "So I ran toward the office. And then I saw all the debris in the hallway," he said.

The floor just outside examination room No. 2 -- about 10 feet from where Ciampi had been doing paperwork -- was littered with small pieces of wood, plaster and insulation. Upon inspection, more debris lay inside the room. He saw three chunks of stone on the floor that together formed a rock about the size of a tennis ball, with a glassy-smooth surface. Then he saw a hole about the size of the rock in the tile ceiling, and a tear in the maroon carpet where the rock had landed.

"The first thing we thought was maybe something had fallen from a plane," Ciampi said.

For most of the day, the 10 examination rooms used by Ciampi and two other medical professionals in the practice had been occupied by patients. Had the falling object crashed through the ceiling a little earlier, it might have killed someone.

"I thank God," Ciampi said.

Later, he said, "I was up all night, wondering what it was." No one else in the practice could figure it out, either. Then on Tuesday, the office manager, Rhonda Lawrence, offered a suggestion from her husband Jeffrey, who has a background in geology.

"Jeff said that maybe it was a meteorite," Ciampi said. "We didn't think of that. You know, a meteorite -- that's not the first thing you think of."

Cari Corrigan, a planetary scientist at the Smithsonian Institution's Museum of Natural History, confirmed it.

"It's beautiful," she gushed on Wednesday, after examining the rock.

"The first thing we look at is what's called the fusion crust on the outside," she said. "It's kind of a black, shiny coating, because when it passes through the atmosphere, it's melting a little at a time. So it's like an outer layer of glass, of melted rock."

That, plus flecks of metal in the rock, confirmed it had come from space, she said.

Corrigan said small meteorites hit Earth "fairly often." "We're bombarded by stuff like that all the time," she said. Since most of the planet's surface is uninhabited, most meteorites land a long, long way from people. And most of those that do hit inhabited areas go unnoticed, she said.

Every now and then, though, there's a landing like the one in Lorton. She said the meteorite weighs just over a half pound and probably was traveling about 220 mph when it hit the building.

If the folks at the medical practice want her to, Corrigan said, she will submit the stone to the Meteorite Nomenclature Committee.

"They'll give it an official name and an official description and it'll go on the books as being an official meteorite," she said. "I would imagine it would be called the Lorton, Va., Meteorite, or something like that."