Something strange happened on a stretch of the Curucβ River in the Brazilian rainforest, near the border with Peru, on the morning of August 13th, 1930. The eyewitness detail of what happened was reported to Fides, the Vatican news agency, by a Catholic missionary, Father Fedele d'Alviano, and an account was published in L'Osservatore Romano on March 1st, 1931.
The incident has attracted significant interest from the scientific community only in recent years. Apparently, a meteor fell in Brazil; if this is the case, we must seriously revise our estimations of the probability of such events.
The best-known example of a significant-sized meteor falling to earth in the 20th century happened on June 30th, 1908, when a bolide - a large bright meteor - exploded in mid-air over the Podkamennaya Tunguska river in central Siberia, flattening 800 square miles of forest. The explosion was equivalent to about 10 megatons of TNT.
The Tunguska event mercifully occurred in an uninhabited area and was considered a freak incident that might occur once every 300 years. If something similar happened in Brazil 23 years later, that would knock such estimates out of whack.
The frightened eyewitnesses at Curucβ told Father d'Alviano that, at about 8 a.m., the sun turned blood red, darkness spread overhead and a fine red dust began to fall. Then an ear-piercing whistling screeched through the air, becoming louder and louder, as though signalling the approach of artillery shells. Then large balls of fire fell from the sky and three explosions were heard, each causing earthquake-like tremors. The explosions were audible 150 miles away, and the rain of ash fell until midday.
Father d'Alviano found the local tribespeople very frightened when he arrived on the scene, five days later. One chief convinced many Indians that the end of the world was imminent, and they were about to ingest timp≤, a neurotoxin, to commit mass suicide. Father d'Alviano calmed things down and averted a catastrophe. He explained that bolides, chunks of rock and ice, periodically intercept earth's orbit in space and burn as fireballs in the atmosphere.
Occasional large cosmic collisions with earth, and with other planets, are now accepted as fact. It is widely believed, for example, that a 10 kilometre-wide asteroid slammed into the Yucatβn Peninsula, in southern Mexico, 65 million years ago, with the impact of a 100 million-megaton TNT explosion, precipitating the extinction of the dinosaurs. Also, in 1994, we witnessed large fragments of the comet Shoemaker-Levy 9 crashing into Jupiter.
There is no reason to think we are immune to another large asteroid, capable of decimating or destroying civilisation, hitting earth. We can only hope it will not happen in our lifetime and that, when it does happen, people will have enough warning and a sufficiently advanced technology to be able to destroy or deflect the asteroid before it hits earth.
Large bodies hit our planet about once every 100,000 years, but small bodies, 10-100 metres in diameter, hit much more frequently. We have much to learn about the frequency and effects of these smaller impactors, and we can learn by studying incidents such as Tunguska and Curucβ.
The Curucβ incident was brought to the attention of the wider scientific community in October 1995, by an article in the Observatory by Mark Bailey, director of Armagh Observatory, and three colleagues.
The article collated the published reports of the incident and went on to note that the date of the Brazilian incident coincides with the maximum of the annual Perseids meteor shower. The shower is associated with the large periodic comet P/Swift-Tuttle and contains bodies large enough to produce fireballs.
The darkening of the sun and the whistling preceding the sightings are known to accompany the passage of fireballs. The reports that dust fell to earth before the observed passage of the fireballs is puzzling, but overall Bailey concluded that an exceptional fireball did fall at Curucβ in 1930 and exploded with a power equivalent to about a megaton of TNT.
Bailey's article spurred Ramiro de la Reza, an astrophysicist in Rio de Janeiro, to investigate the Curucβ incident. After enlisting the help of colleagues, he examined satellite photographs of the suspected impact region, noting three possible impact features. The features lie on a north-south trajectory, consistent with the Perseids hypothesis.
De la Reza also examined seismic records for August 13th, 1930. Those showed that major seismic events occurred in the western Amazon on that date. Two events, and a possible third, were detected with measurements typical of impacts. The seismic data record the events occurring shortly after 6 a.m. in the Curucβ River region. Father d'Alviano noted that the event took place "at about eight o'clock". This is a very minor discrepancy, however. Father d'Alviano's note of time could have been a rough estimate. Accurate wristwatches were probably uncommon deep in the Amazon in 1930.
It is important to fully investigate events such as Tunguska and Curucβ. We need to know the nature of the body that fell to earth, whether it exploded in mid-air, how frequent the events are and so on. Bailey estimates that impact events in the kiloton-megaton range occur three to four times per century, which is 10 times more frequent than geologists and astronomers had previously thought.
William Reville is a senior lecturer in biochemistry and director of microscopy at University College Cork