Venus is often called the Earth’s “evil twin” since they’re roughly the same size, formed in the same inner part of the solar system, and happen to be neighbors as well — although, as suggested by that moniker, Venus is horrendously inhospitable to life as we know it compared to our home planet.
The similarities may run even deeper than previously known. Scientists have previously suggested that Venus once had a moon orbiting it, which met its demise when an enormous object impacted with it. Other researchers believe its current lack of moons — beyond several trojan asteroids that don’t directly orbit the planet and therefore don’t meet the definition of a moon — means that Venus never experienced the kind of impact that could’ve dislodged enough material to form a natural satellite.
Now, a new study published in The Astrophysical Journal upends that consensus, with the authors suggesting that Venus did indeed once have a moon — until it spiraled inwards and crashed into the planet’s surface in an apocalyptic demise.
Put simply, Venus may have devoured its own moon.
“My study shows Venus didn’t require a catastrophe to arrive at what we can see today,” said lead author and University of California, Riverside, astrophysicist Stephen Kane in a statement. “It turns out the gravity of the planet itself combined with the rate at which it spins naturally caused the moon to collapse on top of it.”
The findings could have significant implications, even when it comes to investigating the habitability of distant worlds.
“When people think about Earth twins around other stars, one question they ask is, ‘Does it have a moon?’” Kane said. “”My study shows a disturbing scenario for many of those cases. If these planets don’t rotate fast enough, the moon will crash to the surface, and that would change the course of history for those planets.”
Moons don’t always have a perfectly stable orbit. We know that our own Moon is moving away from us at roughly two inches a year, the result of the Earth’s relatively fast spin. Venus, on the other hand, takes far longer than 24 hours to complete a rotation, completing one revolution every 243 Earth days.
That sluggish spin means that a hypothetical moon may not have enough energy to escape Venus’ graviational pull, and would be doomed to collide with its surface eventually.
Kane and his team used computer simulations to simulate this behavior, based on the interaction between the Earth and the Moon and consistently found that the moon would succumb to Venus’ slow rotation.
“When I made this discovery, I was shocked,” Kane said in the statement. “I thought surely the broad range of scenarios I was exploring would lead to a variety of results. But it all went pretty much in the same direction.”
It’s important to note that the paper doesn’t necessarily mean that Venus had a moon in the first place — but if it did, it likely was devoured by the planet.
Finding direct evidence about the existence of a past moon is extremely difficult. Some 80 percent of Venus’ surface dates back to around a billion years ago, indicating that its geological record may have been wiped out during a major resurfacing event.
Other possibilities include material of a possible moon buried deep beneath Venus’ surface, something that would require extensive research to investigate.
Intriguingly, scientists suggest a major collision that could’ve formed a Venuvian moon could’ve made its once-habitable surface no longer capable of supporting life, turning it into the extremely hot and inhospitable place it’s known to be today.
At the same time, researchers still debate whether a moon is even necessary at all for life to flourish.
“My feeling is there are benefits to having a moon, but it isn’t required for habitability,” Kane explained in his statement. “The moon has definitely changed the way Earth has evolved through time, but we don’t fully know how important that role is.”
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