Science News - January 14, 2012

Bottom of the ocean
Center of the Earth
Center of a neutron star

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the core-mantle boundary, where the mineral may transfer heat from the core into more shallow depths, says Chicago’s Rebecca Fischer. Metallic FeO could also help explain why oxygen dissolves in metal more readily at high pressures, such as in the planet’s core, Fischer’s team reports in an upcoming Geophysical Research Letters.

One new idea, born from some high-
pressure theoretical calculations involv-
ing hydrogen, even suggests that giant
planet cores are slowly dissolving away.
Over time, watery ice in Jupiter’s core
dissolves in the hydrogen-rich material
swirling above so that the core shrinks,
Wilson and Burkhard Militzer, also of
Berkeley, write in an upcoming Astro-
physical Journal. “ What’s going on inside
Jupiter is more complicated and less
homogeneous than had been taken into
account in previous models,” Wilson says.
The work may even
shed light on planets
in other solar systems,
which astronomers
have glimpsed only
indirectly so far. Many
known exoplanets are
more massive than
Jupiter, and so they
are also hotter inside.
Cores of these exo-
planets would have
started eroding away
even faster than Jupiter’s, Wilson says.
As a result, elements may have leached
from the core and become well-mixed in
the gassy atmosphere. One day, if astron-
omers on Earth can get a detailed picture
of an exoplanet’s atmosphere from afar,
they may need to account for such inter-
nal chemical mixing in order to properly
understand what they’re seeing.

Here on Earth, scientists put
on the pressure with a device
called a diamond anvil cell.

The world of high-pressure discovery also extends well beyond Earth — to other planets in the solar system, and on to other planetary systems. In particular, the cores of gas giant planets are “the least accessible but in many ways the most important objects in the solar system,” says Hugh Wilson, a planetary chemist at the University of California, Berkeley. The very existence of the cores allowed Jupiter and Saturn to coalesce around them; the gravitational pull of the completed gas giants then helped dictate how the rest of the solar system grew.

Yet scientists don’t know much about how the giant planet cores formed. In principle, they were born as bits of rock and ice swirling around the newborn sun began to glom together, becoming big enough to start attracting hydrogen and helium gas to make up the rest of the planet. Today researchers don’t agree on how big the cores are, much less the conditions that exist inside them.

The squeeze machine
In perhaps the ultimate test of high-
pressure science, researchers are gear-
ing up to squeeze things at the world’s
most powerful laser machine. The three-
football-field-long National Ignition
Facility will focus 192 laser beams on a
single tiny target. The eventual goal is to
fuse the nuclei of hydrogen atoms, thus
harnessing in the lab what the sun and
billions of other stars do daily.