Jupiter Is a Black Sheep Which Protects All Life on Earth

While Jupiter may be our planetary guardian angel, protecting us from harm, gas giants in other solar systems might actually wreak havoc on other exoplanets nearby.

In our solar system, Jupiter's huge gravitational field deflects comets and asteroids away from our delicate, rocky home planet.

However, this gravitational field may put smaller planets in other solar systems at risk of being ejected from their orbits altogether.

"Here on Earth we are protected from asteroids by Jupiter," Danny Price, an astronomer at Curtin University in Australia, told Newsweek.

According to a new study in The Astronomical Journal, small rocky exoplanets similar to Earth may actually be knocked out of the habitable zone by the gravitational impact of large Jupiter-like gas giants.

"It's as if they have four Jupiters acting like wrecking balls, throwing everything out of whack," Stephen Kane, a UC Riverside astrophysicist and co-author of the paper, said in a statement.

The scientists looked into the far-off solar system HD 141399, which has four gas giants situated a long distance from their star, making it a good model for our own solar system, as Jupiter and Saturn are also long way from the sun.

Using computer simulations of the solar system, they found that Earth may not have been able to remain in its habitable orbit had it been in that solar system rather than our own, due to the gravitational effects of the gas giants.

"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," Kane said.

Therefore, multiple giant planets outside the habitable zone may prevent smaller rocky planets from developing life.

Jupiter is the fifth planet from the sun, situated around 484 million miles from our star. At 86,900 miles in diameter, Jupiter is about 11 times wider than the Earth, and has between 80 and 95 moons.

A second paper also published in The Astronomical Journal by Kane and UC Riverside colleague Tara Fetherolf, a planetary science postdoctoral scholar, reveals that one large planet in the middle of the habitable zone would have a similar effect.

The paper looks into a star system named GJ 357, only 30 light years away from Earth, which has a giant planet, called d, situated in the star's habitable zone.

"It's possible GJ 357 d is as much as 10 Earth masses, which means it's probably not terrestrial, so you couldn't have life on it," Kane said. "Or at least, it would not be able to host life as we know it."

Therefore, this large planet would also limit the positioning of a rocky planet like Earth, and likely cause an Earth-like planet to have highly elliptical, oval-shaped orbits.

"In other words, the orbits would produce crazy climates on those planets," Kane said. "This paper is really a warning, when we find planets in the habitable zone, not to assume they are automatically capable of hosting life."

These two papers highlight how lucky we are to exist, as they show how unlikely it is for a rocky planet to happily reside in our star's habitable zone and not only coincide with a large planet like Jupiter, but have it protect us.

Ultimately, the pair of papers shows how uncommon it is to find the right set of circumstances to host life elsewhere in the universe. "Our work gives us more reasons to be very grateful for the particular planetary configuration we have in our solar system," Kane said.

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