A small asteroid of about 1.74 meters and 9.4 tons hit Rio Grande do Sul, Brazil in the early hours of October 1, 2020, generating the super-bolid that turned the night into a day for a few moments. This is the conclusion of BRAMON, the Brazilian Meteor Observation Network that investigated the case. Studies also indicate that this event left meteorites on the ground near Vacaria, in Rio Grande do Sul.

To reach this conclusion, the network researchers analyzed the images from the cameras of BRAMON and Clima ao Vivo, which recorded the bolide that morning.

Trajectory

From the triangulation of the videos recorded in cities in Rio Grande do Sul and Santa Catarina, BRAMON concludes that the bolide had a trajectory predominantly from South-Southeast to North-Northwest. At 01:09 (local time) in the dawn of Thursday, October 1, the space rock reached the Earth’s atmosphere at an angle of 40.5 degress related to the ground, and at 59,600 km/h speed. It started its bright phase at an altitude of 75.3 km east of Caxias do Sul. It continued to shine brightly for 6.2 seconds, largely overcoming the full moon’s luminosity and reaching -17.2 magnitude, a brightness 40 times greater than the full moon, until it extinguishes at 17.3 km of altitude, west of Vacaria.

Superbolide atmospheric trajectory – Credits: BRAMON

Brightness energy and mass

As they travel at a very high speed in space, asteroids and meteoroids have very high kinetic energy. Upon reaching the Earth’s atmosphere, much of that energy is converted into other energies, including the heat that vaporizes much of the object and the luminous energy that makes it visible over huge distances. This process is called atmospheric ablation.

For mass calculations, BRAMON measured the brightness and speed of the meteor in each video frame. From these values, it is possible to estimate the total kinetic energy and, knowing the energy and speed of the object, its mass is calculated by applying the kinetic energy formula (E = m.v²/2).

Speed and brightness X time graph – Credits: BRAMON

From these measurements, it was calculated that the bolide exploded over Rio Grande do Sul with an energy equivalent to 220 tons of TNT. This corresponds to a small asteroid about 1.74 meters and 9.4 tons of mass. Something the size of a Beetle, but a lot heavier and faster too!

Of this mass, it is estimated that between 2% (188 kg) and 6% (564 kg), would have resisted the ablation process and reached the ground in the municipality of Vacaria.

Estimated asteroid size – Credits: BRAMONAll of these calculations involve some estimated values and variables that cannot be measured, being replaced by standard values indicated in the scientific literature. This means that the results presented are an approximation of reality and may not accurately represent it.

Meteorites strewn field

From the trajectory calculated by BRAMON, the American engineer Jim Goodall calculated the strewn field of ​​the meteorites.

When the object reaches the lower and denser layers of the atmosphere, the air resistance is so high that the object explodes, generating a burst of brightness and an intense shock wave, which is perceived as a strong explosion noise. At that moment, the rock breaks into hundreds, perhaps thousands of fragments, most of which have a few grams of mass. These fragments travel to the ground practically at a constant speed of around 300 km/h and are subject to winds that interfere a lot in the trajectory, mainly of the smallest fragments.

To calculate the strewn field, the software developed by Goodall, simulates the trajectory of a cloud of fragments of different sizes and shapes, considering both the meteor’s trajectory and the winds present in the region. The map below represents the regions where it is possible to find the meteorite fragments generated by this bolide.

Meteorites strewn field – Credits: Jim Goodall / BRAMON

The yellow arrow represents the end of the meteor’s trajectory, the area in blue marks where there is the possibility of finding these meteorites. This possibility is litle higher in the green area and the yellow area, it is where there is the greatest probability. The area is largely in the municipality of Vacaria, but extends from Campestre da Serra, further south, to Muitos Capões, to the northwest. The smallest fragments are also more numerous and therefore easier to find. They must have spread over a large part of the dispersion area closest to Vacaria and Campestre da Serra, while the larger and less numerous fragments may be found closer to the Muitos Capões.