[2][3] In 1990, Captain Ruben Lianza of the Argentine Air Force, an amateur astronomer, provided a report to an astronomy publication that included aerial pictures of a set of odd teardrop-shaped depressions near the city of Río Cuarto, Córdoba in north-central Argentina.

The depressions seemed very similar to the sets of craters produced in laboratory simulations of impacts taking place at low angles.

A team of American researchers went to Argentina to investigate, collaborating with Captain Lianza and Argentine academics to study the strange depressions.

The depressions were thought to be due to a grazing impact of a set of objects at a very low angle, which calculations show to be a rare occurrence.

[3] There is no doubt that there is impact material in the form of glassy impactite and shocked quartz in the Río Cuarto structures.