A new analysis has shown that in the last million years alone, Earth has experienced at least four impacts from celestial bodies larger than a kilometer in diameter. If these conclusions can be confirmed, it will turn out that we greatly underestimated the level of asteroid threat to our planet and civilization.
Fall of a large asteroid could be extremely dangerous for life on Earth and even more so for our civilization. In the past, they have repeatedly caused global and local disasters. However, it is not easy to estimate the frequency of such impacts: geological activity of the planet and erosion quickly erase all traces. Therefore, scientists usually focus on the evidence, which is not on the surface of the Earth, but on the Moon.
It is close and should receive about the same number of impacts, and their craters are preserved for many millions of years. Another source of risk information is provided by the number and size of near-Earth celestial bodies that could potentially collide with our planet. Such calculations show that asteroids and comets larger than a kilometer fall to Earth every 600-700 thousand years on average.
However, the new work carried out by scientists from NASA Goddard Space Flight Center, gives much more frightening values. According to their data, only in the last million years, the Earth has experienced at least four impacts. The report was made at the recently held 54th Scientific Conference on the Moon and Planets (LPSC).
Using satellite images and lidar scanning data from different angles, James Garvin and his colleagues produced 3D maps of four large craters with a resolution of up to four meters. Then they analyzed them using an algorithm designed to search for circular structures on the surface of Mars. The system found traces of a circular shaft located much farther away than those found before and undetected in past work.
All four craters studied were much larger than previous estimates. For example, the diameter of the crater Pantasma (Nicaragua, age about 800 thousand years), according to new data, is not 14.8 kilometers, but more than 35; crater Zhamanshin (Kazakhstan, 870 thousand years) "grew" from 13 to 30.4 kilometers. These figures indicate that the craters were left by much more massive celestial bodies than previously thought.
It is possible that the craters examined by Garvin and his co-authors appeared as a result of the fall of objects larger than a kilometer in diameter. At the same time, the age of the oldest of them is a maximum of 1.05 million years. It turns out that during this period of time, the Earth has experienced at least four such impacts. And if to take into account the fact that a large part of the planet surface is covered by oceans, their number could reach 10-11.
The new estimates are radically different from those generally accepted. Therefore, many experts have stated that more serious and weighty arguments are required for proof. It is quite possible that the faint ring structures detected by the algorithm are debris and soil thrown away by the impact and are not related to the craters themselves. Probably they were formed as a result of erosion of ancient craters. New research - first of all field studies, with the study of the composition of local rocks - will help to clarify all this.
