Many of them swing across Earth's orbit on their journey around the sun. Astronomers estimate that one hits the Earth about once every 100 years--none has hit Earth since 1908, when a 20-megaton blast leveled 700 square miles of forests of central Siberia in an impact called the Tunguska Event. In that incident, a massive pale blue fireball exploded high above the Tunguska River valley in Siberia with enough force to knock people off their feet 40 miles away.
In the months to come, astronomers hope to gather enough data about the faint and elusive object to calculate its orbit more precisely and to narrow the chance of an impact.
Earlier this week, however, researchers tried and failed to track the object more precisely with the powerful planetary radar at the Arecibo Observatory in Puerto Rico, according to Chodas and Morrison.
Future observations of the object may yield better computations that should show with certainty whether it will miss the Earth entirely. If astronomers cannot gather enough data to refine their orbital calculations in the next year or so, however, they will have to wait until 2028, when it again comes into range.
"The most likely scenario is that we will get more data that will render all of this invalid and the likelihood of an impact will decrease to zero," Yeomans said.
Even if it turns out that the object is on a collision course with Earth, several experts discounted the need for any emergency action until it returns in 2028.
"My own feeling," said Morrison at Ames, "is that an object this small would not be worth a great effort to deflect it, even if it is on course toward Earth. I don't see an argument for any sort of crash effort."