Posted on 02/03/2007 2:01:40 PM PST by SunkenCiv
Early in our own solar system's history, the largest of these planetary embryos acquired a dense envelope of hydrogen and helium and transformed into the gas giants we know today... Planets that form far from their parent star are expected to have a composition similar to comets (50% rock, 50% water by weight). Once a planet exceeds about ten Earth masses it has enough gravity to attract any hydrogen and helium near its orbit, and will rapidly transform into a gas giant... [A planet] in this region that never exceed the threshold... becomes an "ocean planet", a term coined by Alain Léger (Université Paris-Sud, France) when he first proposed the existence of such worlds in 2003. An ocean planet that stays in the outer disk will probably be captured by the gas giants forming there, perhaps to become a moon like Europa. Such worlds will be composed mostly of rock and ice, and depending on their environment and formation history may harbor liquid oceans below their surface. Hydrodynamic simulations have shown that it is common for planets to migrate inwards or outwards as they plunge through the turbulent gas of the disk. It is therefore quite possible for an ocean planet to creep close enough to its star to melt the ice. So why doesn't our system have any ocean planets?
(Excerpt) Read more at physorg.com ...
Jupiter's Composition Throws Planet-formation Theories into DisarrayExamining four-year-old data, researchers have found significantly elevated levels of argon, krypton and xenon in Jupiter's atmosphere that may force a rethinking of theories about how the planet, and possibly the entire solar system, formed. Prevailing theories of planetary formation hold that the sun gathered itself together in the center of a pancake-shaped disk of gas and dust, then the planets begin to take shape by cleaning up the leftovers. In Jupiter's current orbit, 5 astronomical units from the sun, temperatures are too warm for the planetesimals to have trapped the noble gases. Only in the Kuiper belt -- a frigid region of the solar system more than 40 AU from the sun -- could planetesimals have trapped argon, krypton and xenon.
by Robert Roy Britt
Nov 17 1999
While lead researcher Tobias Owen does not put much stock in the idea that Jupiter might have migrated inward to its present position, other scientists on the team say the idea merits consideration. Owen expects the probes will find similarly high levels of noble gases in Saturn, Uranus and Neptune. Hints of these gases have even been found in the thick atmosphere of Venus, another planet now begging more study.
Death Spiral: Why Theorists Can't Make Solar Systems
SPACE.com | Tue March 28, 2006 | Ker Than
Posted on 03/29/2006 1:21:37 PM EST by SunkenCiv
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