Even though planetary collisions aren’t widely observed today, it’s believed they were once pretty common and they left lasting impacts on the planets in our solar system and beyond.
Uranus is thought to have been a victim of a major collision. Billions of years ago an object, at least twice the mass of Earth, crept up a little too close to young Uranus, and the two bodies slammed into each other with great force. Researchers say the cataclysmic collision was so strong it caused Uranus to shift onto its side. This theory would explain why the planet has an axial tilt of nearly 98 degrees which is far more dramatic than the rest of the planets in the solar system. Fortunately, Uranus managed to maintain the majority of its atmosphere so it’s still around today. However, not all planetary masses survive impacts on this scale.
Earth is thought to have been at the center of a catastrophic collision that destroyed another planet. The Giant Impact Hypothesis - aka The Big Splash or the Theia Impact - suggests that an object about the size of Mars moved towards Earth more than four billion years ago. It then slammed into our protoplanet and vaporized on impact. The theory claims that debris from the decimated planet were pulled into Earth’s orbit and over time, the pieces are thought to have clumped together, eventually forming the Moon. While this is estimated to have happened a really long time ago, there are some planetary collisions that are thought to have occurred a lot more recently.
Within the last few thousand years, it’s believed two planets orbiting a young star were involved in a violent, catastrophic collision. The impact annihilated the smaller planet, sending its remains far into space in the form of vaporized rock and metal. Since this was a relatively recent collision, some of the remains are still present and in 2009 NASA’s Spitzer Space Telescope found evidence of the impact. It detected traces of silicon monoxide gas - a product of vaporized planetary crust. Scientists believe the findings help back up the Giant Impact Hypothesis.
So could history repeat itself? Could a planet ever collide with Earth? Scientists say it’s highly unlikely. While large-scale collisions were prevalent when our solar system was young, it would be extremely rare for one to occur in a stable and established system like our own. On top of that, if a planet were to come remotely close enough to threaten Earth, astronomers would be able to spot it years, if not decades, before impact. So, it’s safe to say, we don’t have to worry about a rogue planet obliterating our existence... Well, not in our lifetime at least.
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