Once-wild Jupiter may explain our unusual solar system

The neighborhood of our inner solar system may not have always been so lonely.

Blame a wild and unruly young Jupiter, which once caromed like a giant billiard ball, shattering early planets and clearing out a once-crowded community around our sun, UC Santa Cruz astronomers suggest in a new study Monday. “There were collisions — high-speed smash-ups — which made a lot of fragments, hitting other fragments, in a chain reaction,” said researcher Gregory Laughlin, professor and chair of astronomy and astrophysics at UC-Santa Cruz. From their deaths came a big mess of dust and rocky debris — the ancestral ingredients of Earth, Mercury, Mars and Venus.

The theory may explain something astronomers have long puzzled over: why there are no planets inside Mercury’s orbit.

“It’s a totally empty field. A void. Just solar winds,” said Laughlin, whose proposal is reported in Monday’s Proceedings of the National Academy of Sciences. Astronomers no longer believe in the quaint and comforting notion that the solar system was born in its present form — held since before the times of Newton. But the mystery over the uninterrupted vast expanse between Mercury and the sun has deepened as we’ve learned more about other solar systems, thanks to NASA’s Kepler satellite.

This stretch of real estate is plenty valuable elsewhere, we’ve learned. Other solar systems — almost 500, at last count — typically have many planets orbiting much closer to their host star than Mercury does to ours.

These solar systems also tend to have giant planets, like Jupiter, dubbed “The King of Planets,” much closer to their suns.

“It shows we’re special. An anomaly,” said Laughlin. Laughlin and coauthor Konstantin Batygin of the California Institute of Technology set out to learn why, asking: What happened in the early evolution of our solar system that created such anomalous architecture? There’s no way to witness the actual event, of course — it took place in the first 1 to 3 million years after the formation of the sun, nearly 4.5 billion years ago. (In human terms, that would be the first weeks of life for a centenarian.)

Using pencils, papers and computers, they recreated what would have happened if we started out like other solar systems, with a set of rocky planets with close-in orbits.

The UCSC analysis explores some of the consequences of a 2011 theory of dramatic giant planet migration, called “The Grand Tack.” That scenario, posited by another team of astronomers, is modeled after tacking yachts, blown from one side to another.

But instead of drifting like a graceful ship, the astronomers theorized, Jupiter did a death dive, sweeping through the early solar system like a wrecking ball, creating a cascade of collisions from its gravitational field — and plowing the whole mess in towards the sun.

Then Saturn’s gravitation sucked Jupiter back, and it retreated into its now-mannerly orbit. The Grand Tack knits together many aspects of our solar system that had defied explanation, such as why the inner planets have chemical makeups so different than that of larger “outer” planets.

But now, UC-Santa Cruz researchers believe Jupiter’s wild ride could have been much more destructive, smashing nascent planets into smithereens, including newly-formed Super Earths.

Then a second generation of inner planets — Mercury, Venus, Earth and Mars — formed out of the debris left behind.

Full report: http://www.dailydemocrat.com/general-news/20150323/once-wild-jupiter-may-explain-our-unusual-solar-system/3

“Then Saturn’s gravitation sucked Jupiter back, and it retreated into its now-mannerly orbit.”

I have trouble picturing this. Would Saturn’s gravity be enough to lure the giant back?

i probably would depend where in the orbits of the two they interacted.

Oh of course! I was thinking of their current orbits. Der.

> Our Atypical Solar System Due to Wrecking Ball Jupiter?

In a word “no”.

1. Our solar system is atypical in having nice uniform circular orbits for all the planets. That’s the exact opposite of what would happen with a Velikovsky-inspired “wrecking ball”.

2. Certainly Jupiter could have migrated inwards in the early Solar System, due to gas drag in times before the Sun started producing copious UV light in its T-Tauri stage, but it could NOT have migrated back out. The suggestion that the tidal effects of Saturn could have pulled Jupiter out are pure rubbish.

3. The formation of the inner solar system, out to Mars is extremely well understood and has been accurately simulated by the cold accretion of planetesimals. The calculations have gone all the way to getting correct isotopic composition of noble gases in the atmospheres of all the inner planets. No catastrophic intervention necessary.

4. The biggest mystery (of three that I can name) about Solar System formation is the formation of the outer planets Uranus and Neptune. They’re larger than standard models of Solar System formation will allow. My guess is that that’s because the early Sun had periods of time when it was hotter than it is at present – the outer planets form faster if the Sun is hotter. The stupid “wrecking ball Jupiter” hypothesis doesn’t even begin to explain the origins of Uranus and Neptune.

5. The inwards migration of Jupiter-sized planets is suggested by the observations of exoplanets, but even that is not proved – the orbital radius distribution of large exoplanets is similar to that of binary stars, and nobody suggests that close binary stars are formed by the inward motion of stars due to gas friction. Instead, close binary stars are created when the angular momentum of the collapsing cloud is too big folr the formation of one star and so the central star splits in two. Exactly the same mechanism can be used to explain the prevalence of hot Jupiters in exoplanetary systems. No inward motion is necessary.

6. In all this it is necessary to keep in mind that in most hot-Jupiter exoplanetary systems the “hot-Jupiter” isn’t a planet. It’s a brown dwarf. Transiting studies that have led to the discovery of these hot-Jupiters are unable to distinguish between a Jupiter-sized planet and a brown dwarf. Given that there are known to be far more stars in close orbit than planets in close orbit, it makes sense that most of the hot-Jupiters are star-like (heavy brown dwarfs with a mass approaching 75 times that of Jupiter) rather than planet-like.