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| Titel |
Formation of Saturn and Jupiter and their Atmospheres |
| VerfasserIn |
S. K. Atreya, J. I. Lunine, A. A. Simon-Miller, D. H. Atkinson, W. B. Brinckerhoff, A. Coustenis, P. R. Mahaffy, T. R. Spilker, A. Colaprete, K. Reh |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061086
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| Zusammenfassung |
| The heavy elements (> 4He) in the well-mixed atmosphere are key to understanding the
formation of Saturn and Jupiter and the origin and evolution of their atmospheres. The
conventional model of the giant planet formation, known as the core accretion model,
requires first the formation of a substantial core of 10-15 Earth masses, followed by
gravitational capture of the most volatile of gases, hydrogen, helium and neon.
The core is made from gradual agglomeration of grains of rock, metal, ice and the
volatiles trapped in them. During accretionary heating, volatiles are released from
the core and form the atmosphere together with hydrogen, helium and neon. The
above formation scenario implies solar abundances of heavy elements, as does the
gravitational instability model. However, the heavy elements (relative to H) in Jupiter’s
atmosphere were determined by the Galileo probe to be enriched by a factor of 4±2
compared to the sun. Galileo is the only probe ever to enter a giant planet to make in
situ composition measurements. Moreover, the inter-elemental ratios were uneven,
hence non-solar. One key elemental ratio, O/H, could not be determined as the
probe entered a meteorologically anomalous region that was exceptionally dry. The
O/H ratio is a key missing piece of the formation puzzle, however, as water was
presumably the original carrier of heavy elements that formed the core and could
have made up more than half of the core mass. This situation will be rectified in
2016 when the Juno microwave radiometer (MWR) experiment measures and maps
Jupiter’s water abundance to pressure levels of several hundred bars, hence the O/H
ratio.
Unlike Jupiter, the only reliable data presently available for Saturn are on C/H from
methane, and P/H from phosphine in the upper troposphere/stratosphere by remote sensing.
However, P/H in this region is not a good indicator of either the deep P/H or the
enrichment of other heavy elements in Saturn, since phosphine is in thermochemical
disequilibrium in the upper atmosphere. If Saturn’s O/H is subsolar, a measurement of
water even at shallow depths could allow its determination. CO could also provide a
handle on O/H, but requires a knowledge of vertical mixing in Saturn’s interior. The
measurement of water and phosphine, respectively by the MWR and the Jovian
InfraRed Auroral Mapper (JIRAM) on Juno, together with prior data on CO at
Jupiter will provide a useful guide for determining convective mixing in Saturn as
well. As in the case of Jupiter, an entry probe is essential for determining the bulk
composition in Saturn’s atmosphere, especially the elemental abundances of He, Ne, Ar,
Kr, Xe, O, N and S and the critical isotopes, D/H, 3He/4He, 18O/16O, 13C/12C,
15N/14N, 34S/32S and the isotopes of the heavy noble gases. This would enable
the type of comparative study of Saturn and Jupiter that is crucial to unraveling
the mystery of the formation and evolution of the solar system and, by extension,
extrasolar systems. [www.umich.edu/~atreya to download pdf’s of related publications] |
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