An out-of-this world rock has become the center of a down-to-earth dispute over who its rightful owner should be. The tennis ball-sized meteorite plummeted through the roof of a medical office in Virginia just after dusk on Jan. 18, the same time that people reported seeing a fireball in the sky. It plunged through the ceiling of an examination room and landed near the spot where a doctor had been sitting a short while earlier. “I'm the most likely person to be sitting in that place where it hit,” Dr. Marc Gallini said. He and fellow practitioner Dr. Frank Ciampi say their first thought was to give the rare find to the Smithsonian Institution, which offered $5,000 for it. The doctors are worried, though, that their longtime landlords plan to stake their own claim to the space rock; the collectors market for meteorites can be lucrative. The Lorton meteorite came from the asteroid belt between Mars and Jupiter, curators said.