Asteroid
may be shaken by seismic quakes, as it zips by Earth
An
asteroid which is to hurtle close to the Earth tomorrow may
experience a seismic jolt as it passes through our planet's
gravitational field, scientists suggest.
15
February, 2013
The
45m asteroid, named 2012 DA14, will fly by at 7.8 km/s at a distance
of just 27,000 km from Earth.
It
will be visible in New Zealand skies from about 2.30am (although not
with a naked eye), but will make its closest approach to the Earth
about 8.25am.
It
is forecast to be the closest recorded asteroid, passing well inside
the geostationary ring, where many communication satellites are
located.
While
Earth has experienced many tremors from asteroids striking our
planet, new research by Richard Binzel, a professor of planetary
science at the Massachusettes Institute of Technology, suggests many
near-Earth asteroids experience a seismic jolt when they pass too
close to our planet's gravitational field.
"We
are going to be looking closely for evidence of seismic activity on
2014 DA14 as it passes by," Binzel said. "This is the first
case of an object coming close enough to experience quakes and where
we have enough notice to plan observations."
The
idea of asteroid-quakes came to Binzel when he was pondering a
mystery about "space-weathered" asteroids.
"As
asteroids move through space, they slowly turn dark-red. This
phenomenon, called 'space weathering', is caused by long exposure to
cosmic rays and solar radiation.
For
decades, however, we have known about a handful of small asteroids
that looked [light and fresh]; they were not space weathered."
Calculating
the orbits of the non-weathered asteroids, Binzel and colleagues
discovered they had all had close encounters with Earth in the past
million years.
"We
believe they were 'shaken up' by their encounters with Earth,"
he said.
"Gravitational
forces during the flybys can stretch, rattle, and torque these
asteroids, causing dark, space-weathered material on the surface to
be overturned, revealing the fresh stuff underneath."
Unlike
on Earth, there is no Richter scale for asteroids. Instead, Binzel
measures the force of the quakes in units of gravitational
acceleration, or gees.
"These
asteroids experience [seismic activity] in the milli- to micro-g
range," Binzel said.
"That
might not sound like much, but remember these are small bodies.
Gravity is not very strong, so just a little shaking or stretching
goes a long way."
Binzel
believed an asteroid floating beside an asteroid experiencing such a
quake would see the surface "slowly sway or rock by a few
centimetres".
"Other
things to look for would be puffs of asteroid-dust rising from the
surface and gentle avalanches on the steepest slopes of craters."
MIT
post-doctorate Nick Moskovitz, who works with Binzel, is coordinating
observations with worldwide observatories, including New Zealand's Mt
John Observatory, to determine the colour spin, shape, and
reflectivity of 2012 DA14 as it passes by. Changes in any of these
quantities might be a sign of a quake.
"We
stand to learn a lot from the observations," Binzel said.
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