NASA’s Dart mission will carry out on Monday, November 26 the mission that Leonardo DiCaprio called for with all his wishes in Don’t Look Up. A ship projected at the staggering speed of 24,000 km/h will collide with an asteroid in order to modify its trajectory. This is a simple test, and the small celestial object that will be disturbed by American scientists does not present any danger to the Earth. On the other hand, there are indeed potentially dangerous asteroids (PDA), monitored by scientists.
These include “1994 PC1”, an APD 1 km in diameter, three times the height of the Eiffel Tower. A dimension sufficient to bring about the extinction of humanity. As with all these objects, however, its trajectory is well known to scientists and does not present any danger. On January 18, 2022, it passed 1.93 million kilometers from our planet, five times the distance between Earth and the Moon.
Dangerous from 140 meters in diameter
In March 2020, 1,974 APDs were known. A figure that has increased considerably since 2008, when there were only 982. To be considered potentially dangerous, an asteroid must be more than 140 meters in diameter. In addition, its orbit around the sun must cross that of the Earth within 7,480,000 kilometers of it, or nearly 20 times the distance between our planet and the Moon.
Asteroids measuring more than 1 km have almost all been spotted, according to scientists. They also know 40% of those who exceed 140 meters. If only these large asteroids are considered dangerous, they are also more easily visible. Thus, “2019 OK”, a body the size of a football field, passed on July 25, 2019 “only” 77,000 km from Earth. Due to its small size, it was not detected upstream. If it had crashed, it would have been likely to raze a town.
About 30,000 near-Earth asteroids
As they cross Earth’s orbit, these asteroids are called near-Earth asteroids. In addition to the 1,974 APDs, there are approximately 30,000 near-Earth asteroids of all sizes and several types. The Apollo family asteroids have an orbit larger than that of Earth. Those of the Aton family, on the contrary, have a smaller orbit.
The objects of the Atira family have an orbit entirely comprised within that of the Earth: they therefore do not cross it and present no danger. Ditto for the Amor family, characterized by an orbit entirely outside that of the Earth.
The Sun is shown in yellow. Earth’s orbit is in blue. The red orbits correspond to the orbits of the strict NEOs (1862) Apollo (outer cruiser) and (2062) Aton (inner cruiser). The green orbits correspond to the orbits of the geofrollers (1221) Amor (outer brusher) and (163693) Atira (inner brusher). /Remi Wiki, CC BY-SA 4.0, via Wikimedia Commons
Near-Earth asteroids mainly come from the asteroid belt, located between the orbit of Mars and that of Jupiter, which separates the inner rocky planets from the outer gaseous planets. They could have been ejected by the orbit of Jupiter or a collision for example.