SAN JOSE, Calif. — The neighborhood of our inner solar system wasn’t always so lonely. ADVERTISING SAN JOSE, Calif. — The neighborhood of our inner solar system wasn’t always so lonely. Blame a wild and unruly young Jupiter, which once
SAN JOSE, Calif. — The neighborhood of our inner solar system wasn’t always so lonely.
Blame a wild and unruly young Jupiter, which once caromed like a giant billiard ball, shattering early planets and clearing out the once-crowded community around our sun, University of California, Santa Cruz, astronomers reveal in a new report 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. 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.
The mystery 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 co-author 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 million 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.
They included in their analysis a leading new theory, called “The Grand Tack.”
That scenario, posited by another team of astronomers in 2011, is modeled after tacking yachts, blown from one side to another. But instead of a graceful ship, Jupiter swept through the early solar system like a wrecking ball, smashing nascent planets into smithereens.
Then Saturn sucked it back, and it retreated into its now-mannerly orbit.
Destroyed, this first generation of planets, including newly formed Super Earths, spiraled into the sun, the researchers believe.
Then a second generation of inner planets — Mercury, Venus, Earth and Mars — formed out of the debris left behind.
That may explain why these planets are less massive and have much thinner atmospheres than would otherwise be expected, Laughlin said.
It could also explain why there’s a void inside Mercury’s orbit.
The UC Santa Cruz simulations “may not be the only explanation,” said Laughlin. “But we’re pretty pleased the way it fits together.
“There are all sorts of clues to this big puzzle,” he said. “The job of astronomers is to put these pieces together, and test them.
“Jupiters ‘Grand Tack’ may well have been a ‘Grand Attack’ on the original inner solar system.”
