Context: According to an announcement made by NASA, a giant Near Earth Asteroid called as 163348 (2002 NN4), is expected to pass Earth on 6th June 2020. NASA has also speculated that the passing of this gaint near-earth asteroid will be within the safe limit of distance.
About 163348 (2002 NN4)

• A Near-Earth Object (NEO), the asteroid is called 163348 (2002 NN4) and is classified as a Potentially Hazardous Asteroid (PHA).
• Asteroids with a minimum orbit intersection distance (MOID) of about 0.05 (AU is the distance between the Earth and the Sun and is roughly 150 million km) or less are considered PHAs.
• This distance is about 7,480,000 km or less and an absolute magnitude (H) of 22 (smaller than about 150 m or 500 feet in diameter).

About Near-Earth Object (NEOs)

• NASA defines NEOs as comets and asteroids nudged by the gravitational attraction of nearby planets into orbits which allows them to enter the Earth’s neighbourhood.
• These objects are composed mostly of water ice with embedded dust particles.
• NEOs occasionally approach close to the Earth as they orbit the Sun.
• NASA’s Center for Near-Earth Object Study (CNEOS) determines the times and distances of these objects as and when their approach to the Earth is close.

Significances of NEOs

• The scientific interest in comets and asteroids is largely due to their status as relatively unchanged remnant debris from the solar system formation process over 4.6 billion years ago.
• Therefore, these NEOs offer scientists clues about the chemical mixture from the planets formed.
• Significantly, among all the causes that will eventually cause the extinction of life on Earth, an asteroid hit is widely acknowledged as one of the likeliest.
• Over the years, scientists have suggested different ways to ward off such a hit, such as blowing up the asteroid before it reaches Earth, or deflecting it off its Earth-bound course by hitting it with a spacecraft.

When does a NEO designated as potentially hazardous?

• If a NEO’s orbit crosses the Earth’s orbit, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but a small fraction are comets.
• They are defined as having a minimum orbital intersection distance with Earth of less than 0.05 astronomical units (19.5 lunar distances) and an absolute magnitude of 22 or brighter.
• 98% of the known potentially hazardous objects are not an impact threat over the next 100 years.
• Minimum Orbit Intersection Distance is a method for calculating the minimum distance between two almost overlapping elliptical orbits.
• The Astronomical Unit (AU) is the distance between the Earth and the Sun and is roughly 150 million km.
• The absolute magnitude is a measure of the star’s luminosity i.e. the total amount of energy radiated by the star every second.

Difference between an asteroid and a comet?

• The main difference between asteroids and comets is their composition, as in, what they are made of.
• Asteroids are made up of metals and rocky material, while comets are made up of ice, dust and rocky material.
• Both asteroids and comets were formed early in the history of the solar system about 4.5 billion years ago.
• Asteroids formed much closer to the Sun, where it was too warm for ices to remain solid.
• Comets formed farther from the Sun where ices would not melt.
• Comets which approach the Sun lose material with each orbit because some of their ice melts and vaporizes to form a tail.
• Hence the tail of the comet that we see is nothing but the ice which melts and vaporizzes as the comet approaches the sun.