Russian scientists say they've managed to recover pieces of the meteorite that exploded over the Ural Mountains on Friday, but that much of it fell to Earth in Lake Chebarkul.
A spokesman for the Russian Academy of Sciences told Ria Novosti that the fragments were composed of iron, chrysolite and sulfite.
"We confirm that the particles of a substance found by our expedition near Lake Chebarkul really do have the composition of a meteorite," he said.
Officials have cordoned off the area around the lake to keep out treasure-hunters, with collectors offering thousands of dollars for pieces.
However, Urals Federal University scientists say that the fragments appear to come only from the crust of the meteorite, and that the rest is probably sunk in the lake.
Over the weekend, scientists have revised their estimates of the size of the object up from 49 feet to 55 feet, and its mass from 7,000 to 10,000 tons. It's believed to have released nearly 500 kilotons of energy, disintegrating in just 32.5 seconds.
"Current information, which is not yet complete nor confirmed, points to a small asteroid," says Detlef Koschny, head of near-Earth object activity at ESA's Space Situational Awareness program office.
"There is no way it could have been predicted with the technical means available today. What can be said with near certainty is that this object has no connection with asteroid 2012 DA14."
Asteroid 2012 DA14 made a close flyby of Earth on the same day.
ESA is currently developing a system of automated one-meter telescopes that can image the complete sky in one night, with the aim of identifying objects that pass close to our planet and are large enough to do damage if they enter our atmosphere. The aim is to spot near-Earth objects larger than 40 meters at least three weeks before closest approach to our planet.
"Today's event is a strong reminder of why we need continuous efforts to survey and identify near-Earth objects," says Thomas Reiter, ESA's director of human spaceflight and operations. "Our SSA programme is developing a system of automated optical telescopes that can detect asteroids and other objects in solar orbits."
The impact was the largest reported since 1908, when a meteor hit Tunguska, Siberia. "We would expect an event of this magnitude to occur once every 100 years on average," says Paul Chodas of NASA's near-Earth object program office.