'Skull' Asteroid Skims Past On Halloween
It came within about 300,000 miles of Earth, farther away than the moon but relatively close by cosmic measures.
Astronomers were hoping to capture radar images and other measurements of the asteroid to find out more about its shape, dimensions, surface features and other characteristics.
NASA scientist Kelly Fast said: "The IRTF [NASA's Infrared Telescope Facility] data may indicate that the object might be a dead comet, but in the Arecibo images it appears to have donned a skull costume for its Halloween flyby."
Aside from pure scientific value, the encounter could help develop better tracking techniques and counter-measures for asteroids that may be on a collision course with Earth.
Mr Chodas said: "If we ever had to deflect an asteroid we would need to know a lot about it. And we don't know much about asteroids in general, their structure, how strong they are, are they fill of holes, is it like swiss cheese or are they more solid.
"We really don't know the average density of a lot of the asteroid types so we need to learn more about how asteroids are put together, their structure, if we ever want to deflect one that's headed toward the earth."
Small space rocks rain down on Earth constantly, with most disintegrating as they blaze through the atmosphere.