Rio Cuarto craters
Encyclopedia
The Río Cuarto craters are a group of impact crater
s located in Córdoba Province, Argentina
.
, 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 crater
s produced in laboratory simulations of impacts taking place at low angles. Such features exist on the Moon
, Mars
, and Venus
, but had not been seen on Earth
up to that time.
The depressions had long been known to Argentine geologists, but until Lianza, nobody had seriously investigated them. Samples of materials obtained from the depressions indicated the presence of shocked materials, as well as pebbles that were clearly of meteor
itic origin. A team of American
researchers went to Argentina to investigate, collaborating with Captain Lianza and Argentine academics to study the strange depressions.
There were ten depressions, four of them of substantial size. One crater, named the "Drop", was about 200 meters wide and 600 meters long. Two more large craters, the "Eastern Twin" and "Western Twin", both about 700 meters wide and 3.5 kilometers long, were located 5 kilometers to the northeast. Another major crater, the "Northern Basin", about half and again as big as one of the Twins, was sited 11 kilometers further to the northeast. The long axes of the craters all pointed to the northeast.
A grazing impact, however, will form an elliptical
crater, with sprays of debris that look like butterfly wings. This has been confirmed by high-velocity guns used for impact experiments, and more recently by computer simulations. On impact, the object may shed chunks of itself that fly further downrange to perform secondary impacts.
Models of the Río Cuarto event suggest that the object struck at an angle of no more than 15 degrees from the horizontal, with the impact itself having 10 times more explosive energy than the Barringer Crater event and 30 times more than the Tunguska event
. Although the age of the craters has not yet been determined precisely, it is believed they are about 10,000 years old, placing them at the start of the Holocene
.
. The object hit ground at the Northern Basin, creating a mountain of fire about 10 kilometers wide and 50 kilometers long, and scattered off pieces that went downrange to form the Twins and the Drop. The fireball incinerated all life downrange in a firestorm with a parabolic-shaped footprint that created hurricane-force winds, erasing the butterfly-shaped pattern of debris characteristic of such low-angle strikes.
The object was thought to be a "carbonaceous chondritic
" asteroid
, largely made up of simple carbon compounds and resembling something like a big lump of soot. The impact probably released huge clouds of toxic carbon monoxide
that killed off wildlife in the area, assisted by heavy concentrations of toxic nitric oxide
s created through ionization by the object's fiery passage through the atmosphere. It is likely the impact resulted in serious atmospheric effects and may have even had a short-term effect on global climate.
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
s located in Córdoba Province, Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
.
Discovery
In 1990, Captain Ruben Lianza of the Argentine Air ForceArgentine Air Force
The Argentine Air Force is the national aviation branch of the Armed Forces of the Argentine Republic. , it had 14,606 military and 6,854 civilian staff.-History:...
, 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
Río Cuarto, Córdoba
-References:* - Official website....
in north-central Argentina. The depressions seemed very similar to the sets of crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
s produced in laboratory simulations of impacts taking place at low angles. Such features exist on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
, Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
, and Venus
Venus
Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
, but had not been seen on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
up to that time.
The depressions had long been known to Argentine geologists, but until Lianza, nobody had seriously investigated them. Samples of materials obtained from the depressions indicated the presence of shocked materials, as well as pebbles that were clearly of meteor
METEOR
METEOR is a metric for the evaluation of machine translation output. The metric is based on the harmonic mean of unigram precision and recall, with recall weighted higher than precision...
itic origin. A team of American
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
researchers went to Argentina to investigate, collaborating with Captain Lianza and Argentine academics to study the strange depressions.
There were ten depressions, four of them of substantial size. One crater, named the "Drop", was about 200 meters wide and 600 meters long. Two more large craters, the "Eastern Twin" and "Western Twin", both about 700 meters wide and 3.5 kilometers long, were located 5 kilometers to the northeast. Another major crater, the "Northern Basin", about half and again as big as one of the Twins, was sited 11 kilometers further to the northeast. The long axes of the craters all pointed to the northeast.
Formation
The craters 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. Most impacts will strike at an angle of 45 degrees to the horizontal or greater, and the impact craters will always be close to circular, since the shock wave that results from the impact propagates symmetrically.A grazing impact, however, will form an elliptical
Ellipse
In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...
crater, with sprays of debris that look like butterfly wings. This has been confirmed by high-velocity guns used for impact experiments, and more recently by computer simulations. On impact, the object may shed chunks of itself that fly further downrange to perform secondary impacts.
Models of the Río Cuarto event suggest that the object struck at an angle of no more than 15 degrees from the horizontal, with the impact itself having 10 times more explosive energy than the Barringer Crater event and 30 times more than the Tunguska event
Tunguska event
The Tunguska event, or Tunguska blast or Tunguska explosion, was an enormously powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai, Russia, at about 7:14 a.m...
. Although the age of the craters has not yet been determined precisely, it is believed they are about 10,000 years old, placing them at the start of the Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
.
Effects
The object came in from the northeast, as bright as the SunSun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. The object hit ground at the Northern Basin, creating a mountain of fire about 10 kilometers wide and 50 kilometers long, and scattered off pieces that went downrange to form the Twins and the Drop. The fireball incinerated all life downrange in a firestorm with a parabolic-shaped footprint that created hurricane-force winds, erasing the butterfly-shaped pattern of debris characteristic of such low-angle strikes.
The object was thought to be a "carbonaceous chondritic
Carbonaceous chondrite
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 7 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites...
" asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
, largely made up of simple carbon compounds and resembling something like a big lump of soot. The impact probably released huge clouds of toxic carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
that killed off wildlife in the area, assisted by heavy concentrations of toxic nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
s created through ionization by the object's fiery passage through the atmosphere. It is likely the impact resulted in serious atmospheric effects and may have even had a short-term effect on global climate.