By Charly SHELTON

Yesterday, two asteroids passed within Lunar distance of Earth. Lunar distance, being the distance from the Earth to the Moon, is roughly 238,854 miles. The two asteroids that passed by Earth were even closer than that.
Near-Earth asteroid 2010 RX30 is estimated to be 32 to 65 feet (10 to 20 meters) in size. It flew by the Earth, reaching closest – within 0.6 lunar distances (about 154,000 miles) – over the North Pacific Sea, just south of Japan, around 2:51 a.m. PDT Wednesday, according to Don Yeomans, manager of NASA’s Near Earth Object Program Office at JPL. It was observed by both amateur and professional astronomers with moderate sized telescopes and larger.
The following asteroid was even closer, at 0.2 lunar distances (about 49,088 miles) away. Near-Earth asteroid 2010 RF12, estimated to be 20 to 46 feet (6 to 14 meters) in size, passed closest over Antarctica at approximately 2:12 p.m. PDT.
“It is in the deep south hemisphere, and we may get a few observations, but there are fewer observatories in the south so it won’t be nearly as many (as the first asteroid),” said Yeomans.
“For objects of this size, 10 meters, that’s pretty small. You would expect an object of that size to pass within a Lunar distance on a daily basis,” said Yeomans.  “There are about 50 million of these objects, almost all of which are undiscovered.  So, when I say one of these passes by daily, that doesn’t mean we always see it.”
The Earth was in no danger of being hit by the asteroids, which were discovered Sunday morning by the Catalina Sky Survey in Tucson, Ariz.  But there are about 50 million other undiscovered asteroids out there, and of those known, Yeomans watches dozens for any sign of danger or threat to Earth.
“Anything that gets within 28 million miles of the Earth’s orbit is considered Near-Earth,” said Yeomans. “These two are harmless, but at any given time there are several dozen objects on what we call our ‘Risk Page.’ These are objects that are so poorly known that we cannot yet rule out an Earth impact within the next hundred years.  But usually that’s because their orbits are not well known. That doesn’t mean that we have that many threats; that just means that at any given time there’s several dozen objects that require additional observation so we can get them off our ‘Risk List.’”

  asteroids, Crescenta