Like huge playground bullies, planets like Jupiter can be "agents of chaos" around other stars, a pair of new studies suggest.
Gas giant planets that are the size of Jupiter or larger create havoc in young planetary systems, often shoving smaller, Earth-sized planets way out of their original, circular orbits, according to the new research.
All this instability spells bad news for life on terrestrial planets, as organisms need stable conditions to take root and flourish. Just watch the 2011 film "Melancholia" to get the idea: a planet — once hit by, or veering too close to, a neighbor — will see its climate permanently destabilize.
Take the nightmare scenario of four giant planets that orbit a star known as HD 141399. "It's as if they have four Jupiters acting like wrecking balls, throwing everything out of whack," Stephen Kane, an astrophysicist at the University of California, Riverside (UCR) who authored one of the new studies, said in a Wednesday (Oct. 31) statement.
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While the planetary quartet is relatively far from their star, their presence still would be bad news for an Earth-like planet in the habitable zone (the approximate orbital range where liquid water would be feasible on a terrestrial world's surface).
Computer simulations showed that Earth would have a tough time staying viable with so many big planets nearby. "It's very unlikely," said Kane. "There are only a select few areas where the giants' gravitational pull would not knock a rocky planet out of its orbit and send it flying right out of the zone."
Luckily, Earth doesn't have that kind of "Hunger Games" energy to worry about. In fact, Jupiter's presence in our neighborhood is a boon. The gas giant's strong gravity acts more like a shield, bouncing away comets or asteroids that would otherwise beeline for our little world. But if Jupiter were in the middle of our habitable zone, our solar system might be a lot different.
A star just 30 light-years away from Earth, called GJ 357, was scrutinized in a second, related study t. (By comparison, Alpha Centauri — the closest planetary system to us — is roughly four light-years away.)
New estimates of a habitable zone planet, known as GJ 357 d, show that it's perhaps 10 times more massive than Earth, nearly double the previous estimate. Such a heavyweight would likely prevent Earth-size planets from safely sailing nearby, unless the smaller planet's orbit was highly elliptical — meaning that the world careens close and then zings far away from its parent star on its pathway in space.
"In other words, the orbits would produce crazy climates on those planets," said Kane, who co-authored the second study with UCR postdoctoral scholar Tara Fetherolf. "This paper is really a warning, when we find planets in the habitable zone, not to assume they are automatically capable of hosting life."
Both of these planetary systems show what could have happened to us if we had too many Jupiters in our neighborhood, or a single Jupiter that came too close. "Our work gives us more reasons to be very grateful for the particular planetary configuration we have in our solar system," Kane said.
Both studies were published last month in The Astronomical Journal. You can find them here and here.
