Dec 31, 2020
THE PRESENCE OF METEORITES IN THE GROUND IS LIKELY
A small asteroid about 7 meters in diameter crashed in the Chinese province of Qinghai on 22 December. Thanks to the Prisma collaboration, coordinated by INAF, and with the use of satellite data that have been made public by NASA’s Cneos, they were able to trace a first identikit of the event.
In this article we will find out where the asteroid that fell on Earth came from, and also where it could be possible to identify the remains of the celestial body produced by the event.
On 22 December at 23:23:33 UTC the US military surveillance satellites managed to identify an explosion in the atmosphere at the coordinates 31.9 ° latitude N and 96.2 ° longitude E. The identified area is located in a region remote mountain range of south-central China, in Qinghai province, near the village of Wayi Xingrong at an altitude of 3800 m.
The explosion that was intercepted was the end of a small, very bright asteroid that marked the sky of the Chinese region, illuminating the surrounding landscape.
Thanks to the data released by Cneos and NASA, it was reported that the asteroid headed towards the ground at a speed of 13.6 km / s, exploding about 35.5 km from the ground. The energy released by the event into the atmosphere was 9.5 kt. To better understand the intensity, the energy emitted during the atomic explosion of Hiroshima was estimated at about 16 kt, so the fallen asteroid had a percentage equivalent to 60% of intensity.
Making a comparison with the total energy emitted by the explosion and the kinetic energy that the asteroid possessed, the latter had about a mass of 430,000 kilograms. Assuming an average density of about 2.5 g / cm3, typical of a rocky asteroid, a diameter of about 7 meters is obtained.
The asteroid, which was comparable to that of about 10 meters that fell into the Bering Sea on 18 December 2018, was therefore quite small and remained unknown until it exploded. The Prisma network by analyzing the speed data, which were provided by US military satellites, was able to determine that the asteroid arrived from the azimuth 351.8 °, on an inclined trajectory of only 4.9 ° on the Earth’s surface. To explain it in other words, the asteroid moved on a trajectory traveled from north to south, grazing the earth’s surface.
Thanks to its inclination, the asteroid managed to persist for several seconds in the atmosphere, thus considerably lengthening the strewn field, that is the region on the ground in which to search for any remains of the celestial body.
During the explosion of a small asteroid in the Earth’s atmosphere, the fragments generally manage to retain their original trajectory, especially with regard to the larger ones, but sometimes the fall towards the ground can be significantly modified by atmospheric winds.
The calculation of the intensity
If we take into account the intensity and direction of origin of the wind, any debris of the asteroid equal to a size of a few centimeters in diameter, has been located in a region around + 31.3 ° N 96.3 ° E, while the fragment of about half a meter should be found at + 30.3 ° N 96.5 ° E.
Between the two points identified there are more than 100 kilometers of distance, therefore a very wide region to be explored and also very inaccessible given that the area has mountains several thousand meters high.
The apparent radian of the asteroid, that is the direction from which it was seen to arrive, would seem to be located in the constellation of Cassiopeia, but this is not the case. In fact, it is not the real direction of arrival from deep space, a condition caused by the Earth’s gravity that has bent its trajectory. The original direction of origin, that is, what astronomers call the true radiant, is located near the star Alpha of the constellation of Andromeda.
It is from the latter that the telescopes positioned on the ground were able to identify the asteroid during the approach phase to the Earth, as also happened with 2008 TC3.
If we take into account the large dimensions and the speed of 13.6 km / s measured by the satellites, everything coincides with a good approximation with the one that the asteroid had outside the Earth’s atmosphere, all data that can be used directly to be able to calculate the heliocentric orbit, that is the original orbit described around the Sun.
The geocentric speed was very low, only 7.8 km / s, while the nominal heliocentric orbit was asteroidal. The celestial body that arrived on Earth came from the Main Belt, which is the main belt of asteroids, a region located in the space between the orbits of Mars and Jupiter.
In conclusion it was only a small near-Earth asteroid which, given its modest size, disintegrated in the atmosphere without any kind of consequences. Probably some small fragments have reached the ground, just waiting to be collected and analyzed in the laboratory.
The use of asteroid fragments that arrive on Earth is a very economical method to analyze them, unlike space missions which are much more expensive such as that of the Japanese probe Hayabusa 2 which brought back to Earth the samples taken from the surface of the asteroid Ryugo.