Near-Earth Objects sweep close to Earth
This is the asteroid Geographos, named in honor of the National Geographic Society. Its orbit sometimes brings it close to Earth, and it is considered a Near-Earth Object. (NASA/ JPL image)
On July 2, 2006, asteroid 2004 XP14 passed not much farther than the moon’s average distance from Earth. There is no danger of this asteroid striking Earth in the foreseeable future. But astronomers – like Judit Ries of the University of Texas – now know and study hundreds of other Near-Earth Objects like 2004 XP14.
Near-Earth Objects are comets and asteroids that will come close to – or even hit – Earth. If they’re large enough, they may pose a threat to humans.
Astronomers discover new objects in the sky almost every night. Judit Ries – an astronomer at the University of Texas at Austin – tries to confirm that some of these really are Near-Earth Objects – or NEOs. Ries points a telescope at where the object is thought to be and takes four images over the course of a few hours. Later, she views them flipping by on a computer screen – like an old-fashioned flip book.
Judit Ries: Since the stars are not moving – at least not during one night – I can line up these exposures. I’ll match up the stars and then blink them in succession. Since the stars don’t move, it looks like I’m just seeing one picture, except there’s this little dot moving across. And that’s what I’m looking for – that little dot moving in the predicted direction.
Astronomers estimate how big a Near-Earth Object is by how bright it is. But this assumes that all NEOs reflect light in the same way. Ries and her colleagues are developing a technique that takes two images at a time – each with a different color filter. These will indicate how reflective the objects are – and ultimately how big they are.
Potentially dangerous asteroids
Read an interview with NASA’s Lance Benner on tracking asteroids that sweep close to Earth.
