The crater is slightly elongated and rests in lacustrine sediments. The crater is about 140 m long and 115 m wide. Several drill cores recovered from the structure revealed that the crater is filled with fine-grained lacustrine sediments. The crater rim is up to 2.2 m high, and it displays internally overturned layers. Apparently, the lacustrine sediments deformed in reaction to the discharged energy of the impact in a plastic way. The radiocarbon analyses have been performed in organic-rich layers, and the relationships among disturbed and undisturbed layers suggest that the impact occurred between the 4th and the 5th century A.D.
The crater is surrounded by a number of smaller craters. These craters are without rim and are interpreted as formed by impacts of fragments that the meteorite lost during its descent in the atmosphere. These smaller craters are up to a few meters deep and several of them display magnetic anomalies, suggesting the possible presence of meteoritic materials. On the other hand, due to the soft nature of the lacustrine sediments, it is very unlikely that the meteoritic fragments rest on the surface today because fragments must have penetrated deep into the ground.
There are about 155 known impact craters on Earth. Many of them are old and deeply eroded. Due to the geologically young age of Italy no impact crater has been found until today. The Sirente main crater is very small compared with most of the other known impact craters. However, due to its young age, the Sirente crater is well preserved. It provide a rare and valuable example of an impact into a soft target.
The press release has been issue by the International Research School of Planetary Sciences, Universita' d'Annunzio, Pescara, Italy.