Earth Woefully Unprepared For Surprise Comet Or Asteroid.
The warning comes from a NASA’s scientist Dr Joseph Nuth, when he addressed the annual meeting of the American Geophysical Union on 12 December 2016. Near-Earth asteroids (NEAs) have Earth-like orbits, so their collisions with Earth tend to be glancing blows from behind or from the side. But comets travel around the sun in more random paths and can thus slam into the planet head-on, with potentially catastrophic results. Comets can be traveling up to three times faster than NEAs relative to Earth at the time of impact, and the energy released by a cosmic collision increases as the square of the incoming object’s speed, so it could pack nine times more destructive power than an asteroid of the same mass. The speed of comets also means that a dangerous one could be nearly upon Earth by the time scientists detect it.
The largest discovered impact crater in the world is known as the Vredefort Dome in Free State, South Africa; its crater has an estimated radius of 118 miles (190 kilometers). The impact date is estimated at 2 billion years ago. This crater was declared a UNESCO World Heritage Site in 2005.
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