A 'PLANET WITHIN A PLANET' by BRIAN MAFFLY
seismometers in boreholes drilled up to 10 meters into granite formations and arranged in patterns to concentrate the signals they receive, similar to the way parabolic antennae work. Pang analyzed seismic waves from 2,455 earthquakes. The way these
EARTH’S INNER CORE IS NOT THE
“The planet formed from asteroids
waves bounced off the inner core
HOMOGENEOUS MASS THAT WAS
that were sort of accreting [in space],”
helps map its internal structure. “This
ONCE ASSUMED BY SCIENTISTS,
says Koper. “They’re running into each
signal that comes back from the inner
BUT RATHER IT’S MORE LIKE A
other, and you generate a lot of energy.
core is really tiny. The size is about
TAPESTRY OF DIFFERENT “FABRICS,”
So the whole planet, when it’s forming
on the order of a nanometer,” Koper
ACCORDING TO GUANNING
up, is melting. It’s simply that the iron
says. “What we’re doing is looking for
PANG, A FORMER DEPARTMENT
is heavier and you get what we call
a needle in a haystack. So these baby
DOCTORAL STUDENT.
core formation. … The reason all the
echoes and reflections are very hard
metals are down there is because
to see.”
“For the first time we confirmed
they’re heavier than the rocks.”
that this kind of inhomogeneity is
The study's biggest discovery is that
everywhere inside the inner core,”
The protective field of magnetic
the inhomogeneity in the inner core
Pang says. Now a postdoctoral
energy surrounding Earth is created
varies. “Toward the center of Earth
researcher at Cornell University,
by convection occurring within the
it tends to be stronger,” Pang says.
Pang is the lead author of a new
liquid outer core, which extends 2,260
Continues Koper, “We think that this
study, published July 5 in the journal
kilometers (1,795 miles) above
Nature that opens a window into
the solid core. The molten
the deepest reaches of Earth. He
metal rises above the
conducted the study as part of his
solid inner core, cools
inner core grew really
doctoral dissertation at the U under
as it approaches
fast. It reached an
the direction of faculty member Keith
Earth’s rocky
equilibrium, and
Koper, director of the seismological
mantle, and sinks.
then it started to
observatory.
This circulation
grow much more
generates the bands
slowly. Not all of the
fabric is related to how fast the inner core was growing. A long time ago the
“What our study was about was
of electrons enveloping
iron became solid, so
trying to look inside the inner core,”
the planet. Without a
some liquid iron could be
says Koper. “It’s like a frontier area.
solid inner core, this field would
Anytime you want to image the
be much weaker and the planetary
interior of something, you have to
surface would be bombarded with
This “planet within a planet” makes
strip away the shallow effects.” The
radiation and solar winds that would
life on the surface possible, at least as
best tools for sensing this hidden
strip away the atmosphere and render
we know it. <
realm are earthquakes’ seismic waves,
the surface uninhabitable.
propagating from the planet’s thin
trapped inside.”
A version of this article was originally published
crust and vibrating through its rocky
For the new study, the team looked at
mantle and metallic core.
seismic data recorded by 20 arrays of
in @theU.
RESEARCH | 2023
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