In March of 2012, scientists unlocked evidence that Jupiter's
core has been dissolving, and the implications reach far outside of our
solar system. This new data may help to explain a puzzling discovery of
a strange exo-planet. The planet, CoRoT-20b,
was announced in February, and its discoverers searched for a suitable
explanation for its unusual density. Using conventional models, the
astronomers calculated that the core would have to make up over half of
the planet. For comparison, Jupiter's core only represents about between
3-15 percent of the planet’s total mass.
"It's a really important piece of the puzzle of trying to figure out
what's going on inside giant planets," said Jonathan Fortney, a
planetary scientist at the University of California Santa Cruz who was not affiliated with the research.
Conventional planetary formation theory has modeled Jupiter as a set
of neat layers with a gassy outer envelope surrounding a rocky core
consisting of heavier elements. But increasing evidence has indicated
that the insides of gas giants like Jupiter are a messy mixture of
elements without strictly defined borders.
This new research on a melting Jovian
core bolsters a mixing model of gas giant planets and would provide
another avenue for heavier elements to flow throughout the planet.
"People have been working on the assumption that these planets are
layered because it's easier to work on this assumption," said Hugh Wilson, a planetary scientist at the University of California Berkeley and a coauthor of the new research appearing in Physical Review Letters.
Although scientists had previously toyed with the idea of melting cores
in large planets, nobody sat down and did the necessary calculations,
said Wilson.
Scientists have to rely on calculations of Jupiter's core environment
because the conditions there are far too extreme to recreate on Earth.
Wilson and his UC-Berkeley colleague Burkhard Militzer used a computer
program to simulate temperatures exceeding 7,000 degrees Celsius and
pressures reaching 40 million times the air pressure found on Earth at
sea level.
Those conditions are thought to be underestimates of the actual
conditions inside Jupiter’s core. Nonetheless, the authors found that
magnesium oxide -- an important compound likely found in Jupiter's core
-- would liquefy and begin drifting into Jupiter's fluid upper envelope
under these relatively tame conditions.
Researchers believe that similarly-sized gas giant exoplanets --
planets found outside of our solar system -- probably have similar
internal structures to Jupiter. Consequently, scientists were baffled
earlier this year when they found a planet with approximately the same
volume as Jupiter yet four to five times more mass.
CoRoT-20b's core presented a huge problem for traditional assumptions
surrounding planet formation. "It's much easier to explain the
composition of this planet under a model where you have a mixed
interior," said Wilson.
Even the team that discovered the planet noted that a mixing model
could allow for a more palatable planet density. Wilson's simulations
not only add credence to the mixing model of giant planets but also
suggest that this specific exoplanet's core is probably melting just
like Jupiter's.This melting may help explain why the exoplanet's heavy
elements are likely stirred up and distributed throughout its volume,
said Wilson.
Santa Cruz's Fortney agrees that most of the exoplanet's heavy
elements likely reside in the outer envelope. Nonetheless, he expects
other factors played a larger role in how the planet's interior became
mixed: "It's more of a planet formation issue."
Several other events, such as two gas giants colliding together,
might explain the ultra-high density of this new planet, Wilson admits.
Certain processes may also limit the effectiveness of the melting and
mixing process.
Liquefied parts of a gas giant's core may have trouble reaching the
outer envelope due to double diffusive convection -- a process commonly
found in Earth's oceans. When salty water accumulates at the bottom of
the ocean, its density keeps it from mixing thoroughly with the upper
layers. In a similar fashion, the heavy elements in Jupiter's core may
have trouble gaining enough energy to move upward and outward.
Scientists don't know how much this hindrance will affect potential
mixing inside Jupiter, and many other questions remain to be answered
about the melting process.
"The next question is, 'How efficient is this process?'" said Fortney.
Researchers will have more tools to answer this question once NASA's Juno probe
reaches Jupiter in 2016.
With the spacecraft's instruments carefully
analyzing Jupiter's composition, Wilson believes that there will be
signatures of mixing and core erosion.
The Daily Galaxy via Inside Science News Service
Image courtesy of NASA/JPL
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