Though we do not perceive imminence of any big sized asteroid to hit the Earth even over the next two or three hundred years, it is a matter of great relief that ESA (European Space Agency) and NASA  have joined hands to test whether we may deflect any asteroid that may spear into our planet, midway so that it did not smash on the Earth.
Though it would be better if we may equip ourselves to protect the Earth from their invasion through appropriate technology, the most challenging thing about them is the fact that they hit the Earth just in a wink.
As we know, in those days, we did not have the necessary wherewithal to know in advance whether any foreign celestial body was heading toward the Earth and if so, whether it was likely to hit the Earth or was likely to zoom past it just like a storm as we, probably, are now in possession.
As compared to what happened when jet planes had hit the Twin Towers, the damage done by these planes was not even a millionth fraction of the damage we may incur if an asteroid measuring more than 30 metres ever hits the planet, if you knew how big craters were created by various asteroids that have hit the Earth from time to time such as the one known as “Vredefort Crater” of South Africa that measures about 300 kilometres across when an asteroid is believed to have hit the Earth about 2 billion years back.
Steps being taken by ESA and NASA to evolve an “Earth Defense System”
NASA has been planning a project along with ESA, that it calls the “Double Asteroid Redirect Test” (DART) to test whether it is possible to deflect the course of an incoming asteroid by shooting a nuclear projectile at it on its way itself so that it did not hit the Earth.
For this test-run, they have chosen an asteroid known as “Didymos” and a much smaller rock orbiting it called “Didymoon” situated about 11.2 million kilometres away from us in the Asteroid Belt.
“Didymos” has been chosen for this purpose because it happens to be a binary (having a moon) asteroid measuring about 17 kilometres, in diameter, it is large enough to wreak havoc across a wide swath of Earth if it knocked down on the Earth.
ESA has stationed a probe named “Hera” around “Didymos” and “Didymoon” and NASA plans to launch a spacecraft to circle the asteroid between 2020 and 2021 so as to dash a projectile against “Didymoon” in October 2022.
Once that’s done, a year later – the ESA probe will be commissioned to determine how successful the course-correction may have been.
Though they have no idea what other technique could be possibly employed if this trial fails but they plan to use this technique even for larger asteroids if it succeeds.
But, just imagine – how lucky we are that some asteroid should have hit the Earth in a manner that the Earth should have started rotating around its axis since we would not have had “days and nights” on the Earth if it would not have been spinning around its axis.