| Subject: Jupiter's core |
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Blobrana
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Date Posted: 19:11:23 12/14/04 Tue
Katharina Lodders, Ph.D., Washington University in St. Louis research associate professor in Earth and Planetary Sciences in Arts & Sciences have proposed a new mechanism by which the planet Jupiter formed 4.5 billion years ago after studying data from the Galileo probe.
The widely accepted model for Jupiter's formation assumes that its overall composition is similar to that of the Sun, with enrichments of oxygen and other elements heavier than helium. Jupiter's core was believed to be a massive snowball that formed in the cold reaches of the outer solar nebula, the gas and dust cloud from which the solar system formed. However, the Galileo probe mass spectrometer found much less water than expected in Jupiter's atmosphere.
Taking the mass spectrometer data and earlier Earth-based infrared spectroscopic measurements at face value, Lodders calculated that Jupiter is depleted in water and thus in oxygen. The Jovian oxygen inventory is only about half of the oxygen elemental abundance in the Sun. On the other hand, the Galileo probe mass spectrometer data show that Jupiter's carbon inventory is about 1.7 times larger than that in the Sun. Based on these data; it seems that Jupiter's core was mainly tar instead of ice.
Jupiter's core formed rapidly relative to the rate at which gas was lost from the solar nebula. Once its core reached about 10 Earth masses, gravitational attraction captured the surrounding nebular gas and built up the gas giant planet we observe today. The core question is: `If there was a lot of water ice that helped to build the Jovian core, where is the water now? `
"However, you need to build a large proto-core fast, because otherwise you don't have enough mass there to accrete gas and to make a gas giant planet."
However, Jupiter is enriched in carbon, and Lodders notes that there is much evidence for carbon being locked up in organic material on outer solar system planets, comets, and meteorites, and the interstellar medium from which our solar system originated.
Lodders' theoretical model assumes an outer solar system warmer than previously thought. Her theory replaces what astronomers call the "snow line," the point in the solar nebula where water ice condenses, with the new "tar line," the point where asphalt or tar-like material formed, pushing the `snow line` farther out in the solar nebula towards the Kuiper belt.
Lodders proposes that the Jovian core is originally tar and rock, steadily growing to the point where it accretes gas from the solar nebula, primarily hydrogen and helium. Energy from the accretion heats up Jupiter, breaking down the tar and making methane, the third most abundant gas observed in the planet's atmosphere after hydrogen and helium.
"Up to fifty percent of the carbon in the interstellar medium may be in organic solids," she pointed out. "Organic solids are abundant out there and Jupiter is enriched in carbon, so it makes sense to assume that organic solids - instead of water ice - provided the glue to rapidly build the proto Jovian core."
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