The passage of asteroid 2012 DA14 through the Earth-moon system, is depicted in this handout image from NASA.
CAPE CANAVERAL, Fla. - An asteroid as big as a city block shot relatively close by the Earth on Saturday, the latest in a series of visiting celestial objects including an asteroid the size of a bus that exploded over Russia last month, injuring 1,500.
Discovered just six days ago, the 460-foot long (140-meter) Asteroid 2013 ET passed about 600,000 miles from Earth at 3:30 p.m. EST. That's about 2-1/2 times as far as the moon, fairly close on a cosmic yardstick.
"The scary part of this one is that it's something we didn't even know about," Patrick Paolucci, president of Slooh Space Camera, said during a webcast featuring live images of the asteroid from a telescope in the Canary Islands.
Moving at a speed of about 26,000 miles per hour, the asteroid could have wiped out a large city if it had impacted the Earth, added Slooh telescope engineer Paul Cox.
Asteroid 2013 ET is nearly eight times larger than the bus-sized asteroid that exploded over Chelyabinsk, Russia, on February 15. The force of the explosion, equivalent to about 440 kilotons of dynamite, created a shock wave that shattered windows and damaged buildings, injuring more than 1,500 people.
Later that day, another small asteroid, known as DA14, passed about 17,200 miles from Earth, closer than the orbiting networks of communications and weather satellites.
"One of the reasons why we're finding more of these objects is that there are more people looking," Cox said.
Two other small asteroids, both about the size of the Russian meteor, will also be in Earth's neighborhood this weekend. Asteroid 2013 EC 20 passed just 93,000 miles away on Saturday - "a stone's thrown," said Cox.
On Sunday, Asteroid 2013 EN 20 will fly about 279,000 miles from Earth. Both were discovered just three days ago. "We know that the solar system is a busy place," said Cox.
"We're not sitting here on our pale, blue dot on our own in nice safety ... This should be a wakeup call to governments."
NASA has been tasked by the U.S. Congress to find and track all near-Earth objects 0.62 miles or larger in diameter, and estimates about 95 percent have been identified.
However, only about 10 percent of smaller asteroids have been discovered, NASA scientists have said.
The effort is intended to give scientists and engineers as much time as possible to learn if an asteroid or comet is on a collision course with Earth, in hopes of sending up a spacecraft or taking other measures to avert catastrophe.
About 100 tons of material from space hit Earth every day. Astronomers currently expect an object about the size of what hit Russia to strike the planet about every 100 years.