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 Scientists said on Thursday they have observed for the first time
an asteroid breaking apart, crumbling into at least 10 pieces in
sort of a celestial, slow-motion train wreck.
The rocky asteroid, named P/2013 R3, was one of the innumerable
objects populating the crowded asteroid belt located between the
orbits of Mars and Jupiter, roughly three times further away from
the sun than Earth.
Asteroids have broken apart many times over the eons, but never
before have scientists been able to witness it.
This time, however, scientists first noticed the dramatic events
using ground-based telescopes in Arizona and Hawaii and then got a
better look using the orbiting Hubble Space Telescope.
"After looking at the asteroid belt for a couple of hundred years — the first one was discovered in 1801 — to find a new thing like this
is really exciting," David Jewitt, a UCLA astronomer who led the
research, said in a telephone interview.
The findings were published in the scientific publication
Astrophysical Journal Letters.
The asteroid was probably around 2,000 feet in diameter, and no more
than about 3,280 feet in diameter before it began to disintegrate,
Jewitt said. The break-up unfolded over a period of several months
last year, he added.
The Hubble telescope detected at least 10 fragments — each having
comet-like dust tails. The four largest pieces each had a diameter
of up to about 1,300 feet.
The scientists do not think the asteroid was destroyed in a
collision with another object in part because the way it is breaking
apart — fragments drifting slowly at around one mile per hour — does
not suggest a violent impact.
In addition, the 10 fragments did not all emerge at one time, as
they would in an impact, with their appearance staggered over many
months, Jewitt said.
They also think it is unlikely the asteroid fell to pieces due to
the pressure of interior ices warming and vaporizing because at 300
million miles (480 million km) away from the sun it simply would be
too cold for that to occur.
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Instead, they said the break-up was probably the result of the
subtle but inexorable effect of sunlight over many, many years
causing the asteroid to spin at a slowly increasing rate until it
became unstable and ruptured. This phenomenon, known as the YORP
effect, has been debated by scientists, but never previously
reliably observed.
"This is a really bizarre thing to observe — we've never seen
anything like it before," added Jessica Agarwal of the Max Planck
Institute for Solar System Research in Germany. "The break-up could
have many different causes, but the Hubble observations are detailed
enough that we can actually pinpoint the process responsible."
When hit with sunlight, objects radiate heat back into space. If an
object is perfectly round, that phenomenon would not affect its
structural stability. But the irregular shape of asteroids — often
shaped like a big potato tumbling through space — means that when
sunlight is radiated back into space, it exerts a torque on them,
leading to a spin.
"That net force due to sunlight is very, very weak. But on long time
scales, it can push asteroids around," Jewitt said. "So this is
probably the way asteroids die in many cases. They spin up and blow
themselves apart. And in the process, they make dust and debris that
populates the inner solar system."
(Reporting by Will Dunham, editing by G. Crosse)
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