Near-Earth objects (NEOs) reside in the vicinity of the Earth near 1.0 AU that is the mean distance between Earth and the Sun. Any object like asteroid or comet that orbits the Sun with a perihelion properly inside the orbit of Mars is known as NEO.
Or we can say that Near-Earth object is a small solar system body whose orbit is very close to intersect Earth's orbit or whose orbit brings it to proximity with Earth. It may also pose the danger of collision.
Let us tell you that NASA and its international partners are planning to participate in an exercise that will play out a realistic but fictional scenario of an asteroid on an impact trajectory with Earth. Astronomers on 26 March discovered a NEO and consider potentially hazardous to Earth. Further after few months of tracking astronomers predict that this NEO dubbed 2019 PDC poses a 1 in 100 chance of impact with Earth in 2027 and in real life, the international community has decided that 1 in 100 chance of impact is the threshold for action.
It is also said that Near-Earth objects are small Solar System bodies wich orbits around the Sun and lie partly between 0.983 perihelion and 1.3 aphelion astronomical units away from the Sun. Therefore, it is not necessary that NEO will be near the Earth, but they can potentially approach the Earth relatively closely.
Let us tell you that when NEO is detected by the astronomer’s team like all other small Solar System bodies, it is submitted to the International Astronomical Unions Minor Planet center (MPC) for cataloging.
Comets were the first near-Earth objects that were observed by the humans. When tycho Brahe tried to measure the distance of a comet through its parallax in 1577 then comets extraterrestrial nature was recognised and confirmed. In 1705 periodicity of Comets was recognised when Edmond Halley first published his orbit calculations for the returning object known as Halley's Comet. Do you know that 1758-1759 return of Halley's Comet was the first comet appearance predicted in advance?
In 1898, the first near-Earth asteroid was discovered known as 433 Eros. It is also said that measurement of the orbit of asteroid determine the distance of the Earth and the Sun. It has been said that in 1770 Lexell's comet was the first Near-Earth object.
Asteroid 69230 Hermes was discovered in 1937 when it passed the Earth at twice the distance of the Moon. Hermes was lost that time and was considered as threat but later discovered again in 2003 and said that for another century it was not considered as threat.
Asteroid 1566 Icarus, the 1.4 km diameter asteroid on 14 June, 1968 passed Earth at a distance of 0.042482 AU or 16 times the distance of the Moon.
The 300 diameter Apollo asteroid 4581 Asclepius missed the Earth by 700,000 km on 23 March, 1989. It is said that if the asteroid had impacted it would have created the largest explosion in recorded history which will be equivalent to 20,000 megatons of TNT.
Asteroid namely (35396) 1997 XF was discovered in March 1998, showed a potential 2028 close approach 0.00031 AU from the Earth, well within the orbit of the Moon.
In the exercise done by NASA and their international partners regarding Near-Earth object asteroid can help people in the planetary defence community to understand about the disaster management side and the impacts of asteroid. According to Lindley Johnson, NASA's Planetary Defence officer, this exercise will help us develop more effective communications with each other and with our governments.