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What If Earth Crashed Into Another Planet?

VO: Noah Baum WRITTEN BY: Benjamin Welton
We sometimes take the Solar System for granted. The planets revolve around the sun exactly as they should, and Earth travels its own orbit, along a path that's completely free from danger. But, what if the Earth's course changed, and our world collided with another? What would the damage be? And would anything survive?

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What If Earth Crashed into Another Planet?

It’s our big, beautiful, blue marble in the sky. And we often take it for granted. In fact, it’s hard to imagine what life would be like if a large-scale disaster ever even threatened Earth. But it doesn’t get much more catastrophic than this… What would happen if another planet crashed into us? Or, if the Earth itself switched course, and smashed into Mars, Venus or any of the Solar System’s other major occupants?

Let’s start at the beginning. According to most scientists, Earth (and everything around it) was formed from a chaotic cluster of gas and dust, 4.6 billion years ago. Over time, this gigantic cloud began to collapse and flatten, creating a rotating disk of matter – with the Sun at its center. Next, and this bit is vital, a large clump of wayward material, possibly as big as Mars, crashed into a young version of the Earth, and the collision created our moon – as well as causing our eventual planet to spin on its axis (at an even faster rate than it does today). Of course, literally billions of years have passed between then and now, but his ancient event sent Earth on its way toward becoming the life-harboring haven we live and breathe on today.

But all of it could be undone, were another planet to pummel right into us. For Earth, our three nearest neighbors are perhaps the most likely contenders should a colossal cosmic clash ever happen: Mercury, Venus, and Mars. In 2009, an international team of scientists suggested that all it would take would be a “wobble” in our solar system’s current set-up to bring about a planet-on-planet wreck – and that the rockier planets (Earth included) are most unstable, and more likely to be involved. Luckily, those same scientists also clarified that such a “wobble” isn’t likely to occur for a few billion years yet. But if and when it does, all kinds of chaos will kick off.

Indeed, part of Chaos Theory deals with the unpredictability of unimaginable events occurring, and with how even the slightest of changes can trigger massive destruction. Should the orbit of even one planet alter, it could see the balance of the Solar System fall apart. Even if Earth wasn’t actually struck by anything else, if Mars (and the rest) started passing our planet at a much closer distance, we could see our own route around the sun alter, the effects of our gravity change, and our tides defy everything we expect of them. Failing that, changes on the passing planet could result in projectiles breaking off, possibly heading for us – undoubtedly causing some serious damage.

Should Earth and other planets start travelling an unreliable course, the potential dangers would mount up and up. But even if Earth’s orbit stayed as it is, while the other planets head in different directions, we’d be forever watching the skies in a state of panic. It’d be all eyes on the observatories, while our leading scientists and engineers try to conceive of possible evacuation methods should our telescopes warn of trouble. Elsewhere, we’d all be helplessly hoping that Venus doesn’t veer our way, and that Mercury flies further toward the sun, rather than away from it. Indeed, according to multiple studies by the Paris Observatory and the University of California, Mercury’s future path might prove a real cause for concern – as it could be distorted by Jupiter’s gravity. If that happens, Earth could be its final destination.

So, we’ve scanned the skies for signs of a planet pelting towards us, and then it finally happens. What’s the plan? Well, there isn’t one. And there’d be no real point in making one. Because if the potential prior changes in gravity and atmosphere haven’t already killed us all, then the moment of impact certainly would.

This wouldn’t be your standard apocalypse story, when a few survivors rear their heads after a couple of days of untold carnage, ready to defy the odds and continue their existence. No sir. Should two planets collide, it’s indiscriminate, incontestable, and irreversible damage. The ultimate ‘end of all things’. As mentioned earlier, way back in the Earth’s early days, it’s believed that a massive crash actually made the moon… so the fundamental make-up of our planet could change forever. For a sense of scale, the asteroid that killed off the dinosaurs was about six miles wide; Mercury has a diameter of more than 3,000 miles. For Mars, it’s 4,200 miles. For Venus, it’s 7,500 – only slightly smaller than Earth itself.

The amount of energy that a planet-on-planet hit would generate is almost inconceivable. The dino-ending asteroid reportedly inflicted ten billion times more destructive power than the Hiroshima and Nagasaki bombs. But a meeting with Mercury would comfortably dwarf those explosions. We’re not just talking craters here, but whole sections of the Earth’s crust splintered off, and sent careening into space. These could, in turn, create a series of new moons and satellites gravitating toward our severely battered one-time home – or else, they’d break away and head who knows where.

Amazingly, it’s thought that the event itself shouldn’t drastically alter the orbit of the Earth’s core, but its axial tilt would almost definitely change, as would its rotation speed – perhaps adding thousands of hours to an effective ‘day’. And it’s almost perfectly round shape could be a thing of the past, too. All things considered, life on Earth wouldn’t stand a chance.

Of course, the fact that large parts of our planet would be catapulted off into other parts of the solar system (and space in general) could mean that some essential building blocks for life wind up on another world. Over time, and if the conditions are right, something vaguely resembling human evolution could play out elsewhere, all because our current home was smashed to smithereens. But clearly, the likelihood of that happening isn’t especially high. And if it did, our pretty significant part in the story would be lost to the universe.

It’s not all that bad, though. While planetary collisions are theoretically possible, the odds of them occurring in our star system are incredibly long. And the predictions for when they might happen generally begin billions of years from now. So, don’t worry. Be happy. But spare a thought for anyone on Earth in the far far future… For they could find themselves facing an incomparable Armageddon.

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