NASA tweet, just now: "Asteriods (sic) passing Earth near moon tomorrow morning..no worries." Well, I hope the guys who calculated the trajectory of the two asteroids passing "within the distance of the moon to Earth" didn't make any typos.
Here's the official announcement from NASA:
The Catalina Sky Survey near Tucson, Ariz., discovered both objects on Sunday, Sept. 5. The Minor Planet Center in Cambridge, Mass., reviewed the observations and determined the preliminary orbits. The center's personnel concluded both objects would pass within the distance of the moon to Earth, approximately 240,000 miles. The asteroids should be visible with moderate-sized amateur telescopes.
Neither asteroid will hit Earth. Asteroid 2010 RX30 is estimated to be approximately 32 to 65 feet in size and will pass within approximately 154,000 miles of Earth at 5:51 a.m. EDT Wednesday. The second object, 2010 RF12, estimated to be 20 to 46 feet in size, will pass within approximately 49,000 miles at 5:12 p.m. EDT.
Of course, NASA would always inform of all these near-misses (which should be called "near-hits", Dr. Sagan dixit). Don't expect any "ASTEROIDS GOING TO HIT EARTH! WE ARE DOOMED!" tweets ever. [Twitter]