Just when we thought we'd reached Deep Impact saturation point, astronomers at the University of Hawaii have discovered yet another menace to life on Earth - a new type of asteroid whose orbits lie completely within that of our own. "All other efforts to discover asteroids on a collision course with the Earth are being directed at a region of the sky almost opposite the Sun," says David Tholen, planetary astronomer at the Institute for Astronomy. "The significance of this discovery is that we would have otherwise never found this new asteroid because it apparently doesn't travel to that region of the sky being scanned by other search efforts."
Tholen and graduate student Robert Whitely made the observation from the University of Hawaii's 2.24 metre telescope atop Mauna Kea last February. Scanning the dusk and dawn skies, they came across an asteroid thought to be 40 metres in diameter - similar in size to the one that devastated the Tunguska region of Siberia on June 30, 1908, as well as the iron object that produced Meteor Crater in Arizona 50 000 years ago.
Designated DK36, the asteroid is likely to pass a safe 750 000 miles from the Earth's orbit. "1998 DK36 is nothing to lose sleep over," says Tholen. "It's the ones we haven't found yet that are of concern."
