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The largest planet in our solar system is no stranger to throwing its weight around, both to our benefit and detriment here on Earth.

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[INTRO ♪].

Jupiter is more than twice as massive as all the other planets in our solar system combined, and it has a history of throwing that weight around. In fact, it likely used its gravity to shape the way our solar system looks today.

And that’s generally a good thing for us! We have a nice stable orbit at a cozy distance from our star, and things are usually pretty calm in our planetary neighborhood. So, here on Earth, we have a lot to thank Jupiter for… but it isn’t always the nicest neighbor.

Now and then, it also sends some hazards our way. That makes sharing a solar system with Jupiter … complicated. On a good day, Jupiter’s got our back.

When comets from the outermost reaches of the solar system head toward Earth, Jupiter’s gravity often acts like a shield by chucking them straight into interstellar space. And we’ve even seen Jupiter take some pretty big hits for us. In 1994, fragments of the comet Shoemaker-Levy 9 smashed into Jupiter.

As the impact site rotated into the Earth’s view, scientists could see dark scars on the surface of the planet and plumes of debris rising in its atmosphere. If a comet like this had hit Earth, it would have kicked up an enormous cloud of dust that would have blotted out the Sun and caused mass extinctions on par with the ones that took out the dinosaurs. So not only does Jupiter routinely protect us from comets like Shoemaker-Levy 9, but that dramatic collision gave astronomers a wake-up call—if it happened to our neighbor, it could also happen to us.

Just four years later, in 1998, NASA got serious about tracking near-Earth objects, or NEOs, that could have catastrophic effects if they hit our planet. And now NASA estimates that we’ve found almost all of the thousand or so NEOs big enough to cause apocalyptic worldwide destruction. There are, of course, still plenty of smaller ones that could potentially do some serious damage, but thanks to Jupiter’s wake-up call in the ’90s, we have a pretty good handle on the scariest threats.

So, Jupiter deflects some dangerous comets and reminds us to keep a lookout for incoming asteroids, but the biggest planet in the neighborhood doesn’t always play nice. For example, in 1770, the comet Lexell flew past it, and Jupiter’s huge gravity directed the comet right at Earth. It came within 2.3 million kilometers of us!

That’s how far Earth travels in just 21 hours. So we dodged it by less than a day! And research suggests that this type of event—where Jupiter throws things into the inner solar system rather than sending them out—might be happening more often than we thought.

Like, one simulation of 30,000 space objects showed that Jupiter might even be teaming up with Saturn to send threatening space rocks our way. In the model, each simulated object began in a non-threatening orbit somewhere in the outer solar system. But by the end of the simulation, 8% of those objects were crossing paths with Earth.

And while Jupiter’s gravity was the real culprit slinging objects inward, Saturn was guiding objects toward Jupiter. In the real world, a good deal of Jupiter’s ammo is likely made up of objects called Centaurs. They’re named after the mythical creature that’s half-person, half-horse, and Centaurs are like hybrids between asteroids and comets:.

They can have the same make-up as asteroids, but many of them have comet-like properties like tails of debris. For the most part, Centaurs stick to the outermost solar system. But if they get close enough to Jupiter, the planet’s gravity can alter their path and throw them into the inner solar system, potentially on a collision course with Earth.

Even when it’s not hurling Centaurs our way, Jupiter may make ordinary comets more of a threat than they already are. Although it throws some of them out of the solar system altogether, in other cases, a run-in with Jupiter can tighten a comet’s orbit. That means it’ll go around the Sun faster, giving it more chances to hit Earth.

In fact, that’s exactly what happened with the famous Comet Hale-Bopp. It last swung by the Sun in 1997, and that was the first time it was visible in 4,000 years. But around the same time, an encounter with Jupiter cut its orbital period almost in half, meaning it’ll come by again in just over 2,000 years!

And just to keep us on our toes, Jupiter’s gravity can also pluck rocks from the Asteroid Belt and send them our way too—which isn't very neighborly! But even if we have to give Jupiter a little side-eye now and then, it could have helped make life on Earth possible. During the formation of the solar system, its enormous gravity likely helped carve space for our planet to form in the first place.

And even when Jupiter seemed like our enemy, the space debris it sent our way during Earth’s early years may also have delivered organic material that helped life form. So thanks, Jupiter, for helping to get us going early on! You can stop sending us all those asteroids and comets, though.

Beyond helping us learn how to defend our own planet, understanding Jupiter’s role in our solar system could help us search for life beyond it. When we look for habitable worlds orbiting other stars, it might be useful not just to look for Earth-like planets, but also to see what a Jupiter-like frenemy might be up to nearby. Thanks for watching this episode of SciShow Space!

If you want to learn more about how Jupiter tosses its weight around in the solar system, you might like our video about the group of asteroids Jupiter has held prisoner—possibly for billions of years! You can find out more about Jupiter’s Trojan asteroids after this. [OUTRO ♪].