About once a year, a car-size asteroid enters the atmosphere, though it usually burns up before hitting the surface.

WSJ: Meteorite Hits Russia, Causing Panic

Syria's air and naval forces conducted live-fire manoeuvres aimed testing their readiness to repulse "any aggression against the homeland, " the official Sana news agency reported, with state TV pictures reportedly showing warplanes and helicopters firing missiles at targets in a desert area, as well as surface-to-air missiles hitting targets in the air.

BBC: Syria crisis: 'Nearly 200 lives lost' in last two days

The reason: All four of the top American hopes possess serves and groundstrokes which are strong enough to be weapons on any surface, and the slow, high bounce on clay brings the ball into their hitting zone with sufficient time for them to set up their shots.

WSJ: Americans Produce Feats on Clay