The asteroid 4660 Nereus is en route to Earth, but it won't be the first or the last time: it will come back to approach 12 more times in the next few years.
An asteroid as big as the Eiffel Tower is en route to Earth: NASA specifies that the chances of impact with our planet are practically non-existent, but it keeps a close watch on the large celestial object approaching Earth.
Also because 4660 Nereus, this is the name of the asteroid, is an old acquaintance of the American Space Agency, as well as of the Solar System.
4660 Nereus: a near-Earth asteroid
The large approaching asteroid, which will touch the point of shortest distance from Earth next December 11, was first discovered in 1982 by astronomer Eleanor F. Helin.
Between 1900 and 2100, seven approaches to Earth at distances less than 5 million kilometers have been estimated: the closest will be in February 2060, when Nereus will be about 1.2 million kilometers from the planet.
The second closest passage ever, according to NASA calculations, is scheduled for next December: then the asteroid will be 3.9 million kilometers away from Earth.
Nereus is included in the list of asteroids considered "dangerous" for two distinct reasons: one is in size, while the other - more relevant - in the fact that its orbit is very close to that of our planet.
They are called near-Earth asteroids, literally "close to Earth", there are some tens of thousands of them and only 1500 are considered potentially dangerous, as they not only pass "close" to Earth, but intersect its orbit - the premise of any possible collision.
In 1989, an asteroid of the same type, called 4581 Asclepius, came within 684.000 kilometers from Earth, crossing the exact spot where the planet had been only six hours earlier.
An old NASA acquaintance
The chances of an object the size of 4660 Nereus impacting with Earth are virtually nonexistent, NASA says: statistically, the impact of such an object with Earth occurs every million years, while for larger objects it comes to orders of magnitude of tens of millions of years.
4660 Nereus is the classic ellipsoidal asteroid, and measures about 510 meters long by 300 wide: dimensions similar to those of the more famous Bennu, which was the subject of a mission for the recovery of samples only in 2020.
The so-called near-Earth asteroids are those for which it is more plausible to assume the approach missions and the orbit of Nereus, which makes it approach the Earth with a certain frequency, has already attracted the scientific community.
Nereus was in contention for several exploratory missions: it was supposed to be visited by the NEAP (Near Earth Asteroid Prospector) project, which was never completed, and was among the candidates for the Japanese Hayabusa mission - which was instead directed to 25143 Itokawa.
Nereus was also among the papacies for the mission of NASA's NEAR Shoemaker probe, but in the end it was diverted to the asteroid Mathilde and then landed on 433 Eros.
La ragione potrebbe essere nelle dimensioni, piuttosto contenute in termini astronomici, dell’asteroide e della sua orbita, che renderebbe la manovra per l’avvicinamento ed il successivo rendezvous ancora più complicata di quella necessaria per sbarcare sulla Luna.
4660 Nereus, la cui orbita interseca sia quella della Terra sia quella di Marte, passerà di nuovo molto vicino alla Terra: si prevede che nel prossimo decennio l’asteroide tornerà ad avvicinarsi alla Terra ben 12 volte.
Le speranze per studiarlo più da vicino, quindi, sono tutt’altro che sopite.