Venus is often called Earth’s evil twin due to its size, mass, material composition, and density. It even feels like Venus should’ve become a second Earth. However, it ended up being one of the strangest planets in our solar system. Its surface is hot enough to melt lead, its skies rain sulfuric acid, and its thick carbon dioxide atmosphere crushes anything that tries to land. And these are not even the weirdest things about it. Venus spins just like all planets in our solar system do, but it’s one of only two planets that spin backwards (Uranus being the second one). The planet’s rotation is so slow that a single day lasts longer than its year. Also, Venus has no moons, which is unusual for a planet of its size.
While Earth, our moon, and Mars wear their history in the form of craters, Venus has surprisingly few. It seems as if its surface was wiped clean by massive volcanic resurfacing events hundreds of millions of years ago. It’s like something hit the reset button on Venus, and we don’t exactly know how or why. We know Earth was struck by an object so large that its impact created our moon. Mars’ rugged surface terrain is also scarred by countless impacts. Venus, on the other hand, has always been a mystery. However, there’s a new study coming from the University of Zurich, led by Mirco Bussmann, that explores the idea of Venus being hit by an object the size of Mars.
The bold new study
Imagine witnessing first hand a momentous cosmic smash-up, Venus colliding with a Mars-sized astronomical object. That’s what Mirco Bussmann and his colleagues from the University of Zurich set out to simulate in their study. They used a powerful tool known as Smooth Particle Hydrodynamics (SPH), a computational simulation that treats planetary bodies as a swarm of particles. Each particle carries certain physical traits of a planet, so when planetary objects collide, the researchers can see how materials flow, melt, or spread out in space.
In this virtual laboratory, Venus is not a uniform rock. It consists of an iron core making up about 30% of its mass, cloaked by a silicate mantle comprising the remaining 70%. The scientists then launched various impactors of different sizes. Their massed ranged between 0.01 and 0.1 times Earth’s mass. Then the velocities of the impactors were dialed between 10 and 15 km/s. That means they could observe how the planet would behave if impacted by slow or fast-moving objects. To mimic plausible early conditions of Venus, they varied the planet’s initial rotation rates and thermal states.
At the end of each virtual impact, they measured how Venus’ rotation period — or length of its day, in other words – was altered and how much debris formed a circumplanetary disk, accumulated matter around the planet from which a moon can be formed. The results helped the researchers pinpoint which scenario would most likely turn Venus into the planet it is today.
The conclusion of the study
The researchers from the University of Zurich concluded that a single, massive impact could explain two of Venus’s biggest cosmic puzzles: its slow, retrograde rotation and its lack of a moon. In fact, their simulation showed that a wide range of collision scenarios can lead to Venus spinning the way it does. This includes everything from direct hits when Venus wasn’t rotating to glancing, hit-and-run impacts, with a spinning Venus already in motion.
And the best part is that these impacts that can alter Venus’s spin typically produce no debris disk that could form a moon. Most of the material generated by such an impact would remain close enough to fall right back into Venus’ terrifying atmosphere that NASA wants to someday explore. That means that Venus not having a moon might be the result of a giant astronomical body crashing into the planet.
The study also shows that if a Mars-sized celestial body had hit Venus during the planet’s early history, it could have significantly influenced its unique thermal and geological journey. The impact would dump enormous heat on the planet’s interior, disrupting its mantle and stalling plate tectonics. The stage would be set perfectly for planet-wide volcanic resurfacing. This thermal chaos could explain why Venus appears geologically so young.
