Its small size and orbit meant that it was observed only after it had flown past Earth at about seven times the distance of the Moon.
However, current predictions indicate that on its next flyby, due on 15 February 2013, it will pass Earth at just 24 000 km — closer than many commercial satellites.
"This is a safe distance, but it is still close enough to make the asteroid visible in normal binoculars," said Detlef Koschny, responsible for near-earth objects in ESA's Space Situational Awareness (SSA) office.
The asteroid was discovered by the La Sagra Sky Survey observatory, in the southeast of Spain, near Granada, at an altitude of 1700 m, one of the darkest, least light-polluted locations on the European mainland.
"Considering its path in the morning sky, its rather fast angular motion, the quite faint and fading brightness and its orbit high above the plane of Earth's orbit, it was a slippery target — and easily could have escaped undetected during this Earth visit," said Jaime Nomen, one of the discoverers.
"A preliminary orbit calculation shows that 2012 DA14 has a very Earth-like orbit with a period of 366.24 days, just one more day than our terrestrial year, and it 'jumps' inside and outside of the path of Earth two times per year."
While an impact with Earth has been ruled out on the asteroid's next visit, astronomers will use that close approach for more studies and calculate the Earth and Moon's gravitational effects on it.
"We will also be keen to see the asteroid's resulting orbit after the next close approach in order to compute any future risk of impact," said Koschny. …