Researcher Simulates Characteristics of Planetary Cores of Jupiter, Saturn and Exoplanets

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U of M researcher simulates characteristics of planetary cores
University of Minnesota

What: Getting to the cores of Jupiter, Saturn and exoplanets
When: Published Feb. 17 in Science
Who: Renata Wentzcovitch, associate professor of chemical engineering
and materials science
Contact: Deane Morrison, University Relations, (612) 624-2346
Mark Cassutt, University News Service, (612) 624-8038

MINNEAPOLIS / ST. PAUL (2/17/2006) -- University of Minnesota
researchers Renata Wentzcovitch and Koichiro Umemoto and Philip B.
Allen
of Stony Brook University have modeled the properties of rocks at the
temperatures and pressures likely to exist at the cores of Jupiter,
Saturn and two exoplanets far from the solar system. They show that
rocks in these environments are different from those on Earth and have
metallic-like electric and thermal conductivity.

These properties can produce different terrestrial-type planets, with
longer-lasting magnetic fields, enhanced heat flow to the planetary
surfaces and, consequently, more intense "planetquake" and volcanic
activity.

This work builds on the authors' recent work on Earth's inner layers
and
represents a step toward understanding how all planets, including
Earth,
come to acquire their individual characteristics. The research is
published in the Feb. 17 issue of Science.

In the previous work, Wentzcovitch and her colleagues studied the D''
("Dee double prime") layer deep in the Earth. D'' runs from zero to 186
miles thick and surrounds the iron core of our planet. It lies just
below Earth's mantle, which is largely composed of a mineral called
perovskite, consisting of magnesium, silicon and oxygen. Wentzcovitch
and her team calculated that in D'' the great temperatures and
pressures
changed the structure of perovskite crystals, transforming the mineral
into one called "post-perovskite."

In the new work, the researchers turned their attention to the cores of
the giant planets of our solar system--Jupiter, Saturn, Uranus and
Neptune--and two recently discovered extrasolar planets, or exoplanets,
found elsewhere in the Milky Way. One, referred to as Super-Earth, is
about seven times the mass of Earth and orbits a star 15 light-years
away in the constellation Aquarius. The other, Dense-Saturn, has about
the same mass as Saturn and orbits a star 257 light-years away in the
constellation Hercules.

The researchers calculated what would happen at temperatures and
pressures likely near the cores of the two exoplanets, Jupiter and
Saturn, where temperatures run close to 18,000 F and pressures 10
million bars (a bar is essentially atmospheric pressure at sea level).
They found that even post-perovskite could not withstand such
conditions, and its crystals would dissociate into two new forms.
Focusing on one of those crystals, the researchers discovered that they
would behave almost like metals. That is, electrons in the crystals
would be very mobile and carry electric current. This would have the
effect of supporting the planet's magnetic field (if it has one) and
inhibiting reversals of the field. The increased electrical activity
would also help transport energy out of the core and toward the planet
surface. This could result in more severe activities such as quakes and
volcanoes on the surface. The effect would be much stronger in
Dense-Saturn than in Super-Earth.

The interiors of the icy giants Uranus and Neptune don't exhibit such
extremes of temperature and pressure, and so post-perovskite would
survive in their cores, she said.

"We want to understand how planets formed and evolved and how they are
today. We need to understand how their interiors behave under these
extreme pressure and temperatures conditions. Only then it will be
possible to model them. This will advance the field of comparative
planetology," said Wentzcovitch. "We will understand Earth better if we
can see it in the context of a variety of different kinds of planets."

The work was supported by the National Science Foundation and the
Minnesota Supercomputing Institute.

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