- The closest observed asteroid yet to skim past the Earth
without hitting the atmosphere, was reported by astronomers on Sunday.
- The previously unknown object, spanning five to 10 metres
across, has been named 2004 FU162. It streaked across the sky just 6500
kilometres - roughly the radius of the Earth - above the ground on 31 March,
although details have only now emerged.
- The MIT Lincoln Laboratory's asteroid-hunting LINEAR
telescope in Socorro, New Mexico,US, observed the new object four times
over a 44-minute period, several hours before its closest approach in March.
- Lincoln astronomers, who have discovered over 40,000
asteroids and comets since 1980, quickly recognised the object came exceptionally
close, and posted their findings for confirmation on a web page run by
the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics.
- However, by the time it was posted the object had moved
into the daytime sky, so follow-up observations were impossible and the
listing was quickly removed. A search for prior observations yielded no
- Dissipated harmlessly
- Despite having only four positions for the object, Steven
Chesley of NASA's Jet Propulsion Laboratory was able to calculate its orbit
because it was moving rapidly across the sky.
- He also calculated that the encounter with the Earth
shifted the asteroid's orbit closer towards the Sun. Previously orbiting
the Sun once a year in an orbit that ranged as far inside the Earth's orbit
as outside, 2004 FU162 now has a nine-month orbit centred closer to Venus
than the Earth. The Minor Planet Center published Chesleyís results
on Sunday in its electronic circular.
- "This was an extraordinarily close encounter and
so the orbital change was quite extraordinary. 2004 FU162 was deflected
by about 20 degrees because of the Earth's gravity. I've never seen anything
like that before," Chesley told New Scientist.
- The previous record for the closest asteroid approach
to Earth was set on 18 March by an object called 2004 FH which missed the
Earth by about 40,000 kilometres.
- That was a much larger object, around 30 metres in diameter
- big enough to produce a one-megaton explosion in the atmosphere. Although
it was likely to have exploded so high that the energy would have dissipated
harmlessly. The smaller 2004 FU162 would have burned up as a fireball ending
with a smaller explosion, had it ventured into the Earth's atmosphere.
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