Scientists now seem to be convinced that that it was a meteorite that crashed near Peru's Lake Titicaca over the weekend, leaving an elliptical crater and magnetic rock fragments in an impact powerful enough to register on seismic charts.
As other astronomers learn more details, they too said it appears likely a meteorite hit Earth on Saturday — a rare occurrence.
The Earth is constantly bombarded with objects from outer space, but most burn up in the atmosphere and never reach the planet's surface.
Jay Melosh, an expert on impact craters and professor of planetary science at the University of Arizona, said only one in a thousand rocks people claim are meteorites turn out to be real.
Melosh was skeptical at first, initially calling it a non-meteorite and suggesting the crater might have formed from a volcanic eruption.
Then scientists learned of more details about the crater, as well as witness descriptions of a thunderous roar and a rain of smaller rocks coming down.
"It begins to sound more likely to me that this object could indeed be a meteorite," Melosh said Thursday.
Such impacts are rare and astronomers still want to do other tests to confirm the strike.
Other details don't add up, they said — such as witness accounts of water in the muddy crater boiling for 10 minutes from the heat. Meteorites are actually cold when they hit Earth, astronomers say, since their outer layers burn up and fall away before impact.
Experts also puzzled over claims 200 local residents were made ill by fumes from the crater. Doctors who examined them found no evidence of illness related to the meteorite and one suggested a psychosomatic reaction to the sight and sound of the plunging meteorite.
More details emerged when astrophysicist Jose Ishitsuka of Peru's Geophysics Institute reached the site about 10 kilometres from Lake Titicaca. He confirmed a meteorite caused a crater 13 metres wide and 4.5 metres deep, the institute's president, Ronald Woodman, said Thursday.
Ishitsuka recovered a 7.6-centimetre magnetic fragment and said it contained iron, a mineral found in all rocks from space. The impact also registered a magnitude-1.5 tremor on the institute's seismic equipment — that's as much as an explosion of 4.5 tonnes of dynamite, Woodman said.
Local residents described a fiery ball falling from the sky and smashing into the desolate Andean plain.
Doctors said at the site they had found no sign of radioactive contamination among families living nearby. But they said they had taken samples of blood, urine and hair to analyze.
Peasants living near the crater said they smelled a sulphurous odour for at least an hour after the meteorite struck and it had provoked upset stomachs and headaches. But Ishitsuka said he doubts reports of a sulphurous smell.
Peter Schultz, a meteor crater specialist at Brown University who is eager to visit the Peruvian site, said the latest details suggest this might be an unusual type of meteor strike, and given the crater's size, the original meteoroid had to have been at least three metres in diameter before breaking up.
"With everything I see reported now, it seems to me like we just got hit," Schultz said.