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SagittariusAStar
2012-Jan-06, 03:01 PM
Is Jupiter Eating Its Own Heart?

by Ken Croswell

Jupiter is the victim of its own success. Sophisticated new calculations indicate that our solar system's largest planet, which weighs more than twice as much as all of the others put together, has destroyed part of its central core. Ironically, the culprit is the very hydrogen and helium that made Jupiter a gas giant when the core's gravity attracted these elements as the planet formed. The finding suggests that the most massive extrasolar planets have no cores at all.

Story at http://KenCroswell.com/JupiterCore.html .

Shaula
2012-Jan-06, 04:16 PM
That tagline is a rather .. um .. odd way to put it. The gist of the story is that MgO might be fairly soluble in high pressure phases of hydrogen/helium mix. Since dense stuff still sinks and, as is said, unless there is some very violent convection most of the core material will stay in the core despite its slightly higher mobility.

mantiss
2012-Jan-06, 06:54 PM
That is completely misleading if you ask Me, the ROCKY core being dissolved into a now LIQUID one doesn't change the fact that the core remains, just changes composition, phase etc. To say that some planets have no core makes no sense, you might want to say ROCKY cores.

Swift
2012-Jan-06, 07:30 PM
From the linked story:

Now planetary scientists Hugh Wilson and Burkhard Militzer of the University of California, Berkeley, have performed quantum mechanical calculations to see what happens when magnesium oxide (MgO)--a key ingredient in the rock of Jupiter's core--is submerged in a hydrogen-helium fluid at the planet's heart. The temperature there is approximately 16,000 Kelvin--hotter than the surface of our Sun--and the pressure is about 40 million atmospheres. These conditions are so extreme that no experiment can reproduce them.

According to the team's calculations, magnesium oxide had very high solubility. That means the solid rock in Jupiter's core is dissolving into liquid, as the researchers report in a paper submitted to Physical Review Letters, though the exact rate of erosion is unknown. Wilson and Militzer had earlier calculated that the ice in the core also dissolves. Thus, Jupiter's present core may not be as large as it was when the planet formed.


I have grave doubts about this work. First, what evidence is there that MgO is even present in Jupiter's core? How significant is Mg in the core compared to iron and silicon, for example? And even if Mg is present, would it be in the form of MgO? On Earth, in all likelyhood, I would think Mg would be tied up in things like MgSiO3, which would not necessarily have the same solubility as MgO, even in hydrogen-helium fluid under those conditions.

Second, how good are any calculations under those conditions, so far from what has been experimentally determined?

Romanus
2012-Jan-08, 12:15 AM
In my op, since the jury is still out on whether or not core accretion or cloud collapse is the primary mode of giant planet formation (or indeed if they are both applicable under different circumstances), I can't see the a positive or negative answer for Jupiter's core having much influence on how we should model giant exoplanets.

SagittariusAStar
2012-Jan-09, 05:59 PM
There's nothing misleading here. The article itself states that what happens as Jupiter's rock and ice dissolves is unknown, because the rate of erosion is unknown and the strength of convection is unknown. If convection is strong enough, then some of the core materials have been tossed into the surrounding hydrogen-helium envelope, and so the core is smaller than it was when the planet was born. In more massive gas giants, the core may have vanished altogether.

In any event, the scientists doing this work are expert in the field--and the article quotes two outside experts, who had nothing to do with the work and call the finding important.

As for why study MgO: "it was shown by Umemoto et al that MgSiO3, a major constituent of the Earth's mantle, separates into SiO2 and MgO at giant planet core conditions," according to the second paragraph of the paper on which this article is based.

Hopefully the Juno spacecraft, which reaches Jupiter in 2016, will tell us more about the planet's interior.

Swift
2012-Feb-13, 08:15 PM
Some more data about MgSiO3 phase transformations
R&D Magazine (on-line) story (http://www.laboratoryequipment.com/news-Researches-Use-Lasers-to-Understand-Planet-Formation-021312.aspx?et_cid=2474842&et_rid=54636800&linkid=http%3a%2f%2fwww.laboratoryequipment.com%2f news-Researches-Use-Lasers-to-Understand-Planet-Formation-021312.aspx) about a Physical Review Letters publication

Just as graphite can transform into diamond under high pressure, liquid magmas may similarly undergo major transformations at the pressures and temperatures that exist deep inside Earth-like planets.

Using high-powered lasers, scientists at Lawrence Livermore National Laboratory and collaborators discovered that molten magnesium silicate undergoes a phase change in the liquid state, abruptly transforming to a more dense liquid with increasing pressure. The research provides insight into planet formation.

...

Melts play a key role in planetary evolution. The team says that pressure-induced liquid-liquid phase separation in silicate magmas may represent an important mechanism for global-scale chemical differentiation and also may influence the thermal transport and convective processes that govern the formation of a mantle and core early in planetary history. Liquid-liquid phase separation is similar to the difference between oil and vinegar—they want to separate because they have different densities. In the new research, however, the researchers noticed a sudden change between liquid states of silicate magma that displayed different physical properties even though they both have the same composition when high pressure and temperatures were applied.

The team used LLNL's Janus laser and OMEGA at the Univ. of Rochester to conduct the experiments to achieve the extreme temperatures and pressures that exist in the interiors of exoplanets—those objects outside our solar system.

Glom
2012-Feb-13, 09:26 PM
Would this be a prelude to what happened in 2010: The Year We Make Contact?

neilzero
2012-Feb-19, 05:50 AM
It seems strange to me to talk about rock and ice, if the core temperature of Jupiter is 25,000 degrees k. That sounds like plasma and no compounds to me, or does the extreme pressure prevent plasma? Have we discarded the metalic hydrogen hypothesis? Neil

Shaula
2012-Feb-19, 08:28 AM
For a plasma to form you need to prevent recombination - at high pressures this happens fast so you need high temperatures to maintain the plasma state. A quick look at a phase diagram implies that there may be a 'sweet spot' at about 10g/cm3 where you get plasma but for most pressures hydrogen at that temperature is not ionised.