When straying Jupiter went on the pull

The path of true love never runs smooth, it is said. Especially on Valentine's Day. And for young planets, that path turns out to be an inward-moving annulus.

A simulation by scientists in France and USA appears to show that Jupiter once strayed to flirt with the inner Solar System, before being "jilted" and sent back to its present-day position.

The effect of this was to form the inner planets, according to the theory, which comes up with mass ratios for Earth and Mars similar to that observed today and which, remarkably, also accurately depicts the Asteroid Belt. If the findings are borne out it will mean that our Solar System has more in common with exosolar systems, in terms of the way planets migrate. In other words, our Solar System wasn't always as stable as we thought. Early in our Solar System's formation, the nascent, Gas Giants were bedded snugly inside a protoplanetary disk, like newly-laid eggs in a love nest. However, these eggs had â€˜legs' and wanted to move.

Disk-driven migration meant that the young Jupiter and Saturn lost angular momentum as they were dragged down by gas in the Solar System disk. Like a slowing romance they spiralled ever-further apart, and towards the Sun. According to the simulation, Jupiter could only have moved inwards before Saturn approached its final mass. Like an immature lover, Saturn had let Jupiter slip away. The two planets just needed some time apart.

Jupiter stopped at around 1.5 astronomical units (AU -- one AU being the distance between the Earth and Sun). This is the same distance from the Sun that Mars is today. By this stage the inner planets hadn't formed and Jupiter's effect was to truncate the inner disk to 1 AU.

Gas giants credited for solar system formation
by Maggie McKee
25 May 2005
Jupiter and Saturn form the basis of a "grand unified theory" of the solar system, according to new computer simulations. The research traces three seemingly unrelated phenomena -- the giant planets' orbits, craters on the Moon, and the behaviour of certain asteroids -- to the motions of the two gas giants nearly four billion years ago... an international team of researchers has performed computer simulations that reproduce the orbits of the four giant planets -- Jupiter, Saturn, Uranus, and Neptune -- in exquisite detail. The team has published a trio of papers about their findings in Nature. In the model, the four planets form in 10 million years within the current orbit of Uranus. Surrounding them in a ring are several thousand rocky objects called planetesimals, left over from the formation of the planets... planetesimals begin to "leak" into the giant planet zone and the orbits of the giant planets gradually change. After 700 million years, Saturn has migrated outward and Jupiter inward to the extent that they reach a "resonance" point. This means they begin to march in lockstep with each other, with Jupiter completing two orbits around the Sun for every one of Saturn's. The resonance allows the pair to greatly disturb the orbits of the other planets.
Los Alamos Computers Probe How Giant Planets Formed
Science News
July 22, 2004
Working with a French colleague, Didier Saumon of Los Alamos' Applied Physics Division created models establishing that heavy elements are concentrated in Saturn's massive core, while those same elements are mixed throughout Jupiter, with very little or no central core at all. The study, published in this week's Astrophysical Journal, showed that refractory elements such as iron, silicon, carbon, nitrogen and oxygen are concentrated in Saturn's core, but are diffused in Jupiter, leading to a hypothesis that they were formed through different processes. Saumon collected data from several recent shock compression experiments that have showed how hydrogen behaves at pressures a million times greater than atmospheric pressure, approaching those present in the gas giants. These experiments -- performed over the past several years at U.S. national labs and in Russia -- have for the first time permitted accurate measurements of the so-called equation of state of simple fluids, such as hydrogen, within the high-pressure and high-density realm where ionization occurs for deuterium, the isotope made of a hydrogen atom with an additional neutron. Working with T. Guillot of the Observatoire de la Cote d'Azur, France, Saumon developed about 50,000 different models of the internal structures of the two giant gaseous planets that included every possible variation permitted by astrophysical observations and laboratory experiments.
'Jupiter swallowed planet 10 times the size of Earth'
Deccan Chronicle
August 12th, 2010
Jupiter, the biggest planet in the solar system, might have gained its dominant position after swallowing up a smaller planet... the giant planet, which is more than 120 times bigger than the Earth, has an extremely small core that weighs just two to 10 Earth masses... Jupiter's core might have been vaporised in huge collision with a planet up to ten times the size of Earth... leaving only a fraction of the gas giant's former core behind. This could explain not only why Jupiter's core is so small, but also why its atmosphere is richer in heavy elements compared with the Sun...

most or all are dead links, but I didn't check 'em.

Did Jupiter Bully Other Planets in Sibling Rivalry?
by Robert Roy Britt
8 December 1999
One possible explanation, discussed in Thursday's issue of the journal Nature, is that Uranus and Neptune formed much closer to the center of the action than their current positions might indicate. In this scheme, Jupiter and Saturn were bullies of a protoplanetary playground, shoving the other two future giants out of the way.
Jupiter gave birth to Uranus and Neptune
by Dr David Whitehouse
8 December, 1999
Not too long ago, scientists regarded the orbits that the planets circle our Sun as being the ones they were born in. Now they are realising that this is not the case. Uranus and Neptune may have migrated outwards and Jupiter may have come in from the outer cold. Scientists have always been slightly puzzled by the positions of Uranus and Neptune because in their present locations it would have taken longer than the age of the Solar System for them to form. Scientists from Queen's University suggest that the four giant planets started out as rocky cores in the Jupiter-Saturn region, and that the cores of Uranus and Neptune were tossed out by Jupiter's and Saturn's gravity.
Jupiter's Composition Throws Planet-formation Theories into Disarray
by Robert Roy Britt
Nov 17 1999
Examining 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.

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.

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