India, Feb. 18 -- A NASA scientist has issued a chilling warning for earth. The planetary defense expert said that the earth had no way to defend against up to 15,000 undetected near-earth asteroids, all of which had the potential to wipe out an entire city.

Kelly Fast, a planetary defense officer at NASA, said that what kept her 'up at night' were the 'asteroids we don't know about', as per the Daily Star.

The expert went on to say that it was not the 'large ones' which worried her as much, because they knew 'where they are'. Similarly, the small ones hit the earth 'all the time' and is no cause for concern either. The expert highlighted that it was the rocks that measure about 500 feet that are a cause for concern because they're smal...