Billions of Years Ago, Venus May Have Had a Moon—Which the Planet Promptly Gobbled Up, Study Suggests

The two planets feature similar sizes, masses and structures. One glaring difference between these siblings, however, is that Venus lacks a moon. Scientists suspect it once had one, since space rocks pelted the planet during the solar system’s youth some 4.5 billion years ago.

That’s the leading theory behind how Earth’s moon was born—it formed from debris kicked up by a celestial collision. But some think the second planet from the sun lost its hypothetical satellite in a subsequent crash; another incoming rock may have destroyed it. Now, a team of researchers is proposing a new idea: If Venus ever had a moon, the planet would have promptly gobbled it up.

They published their work September 14 in the Astrophysical Journal. The growing distance is caused by our planet’s relatively fast rotation, whose energy pushes the moon away. By contrast, Venus spins very slowly; one Venus day is 243 Earth days long.

Kane and his colleagues suspected that Venus’ slow spin and gravity could pull a moon inward toward the planet and to its eventual death. The team put this hypothesis to the test with computer simulations, building models based on the physics of how planetary bodies interact through gravity. The researchers initially simulated the evolution of Earth and our moon to confirm that their models could correctly represent a well-understood system.

They then tested what could’ve happened with Venus, inputting different planet rotational speeds as well as variously sized hypothetical moons—from half the mass of Earth’s moon to ten times as massive. In most scenarios, the moon smashed into Venus. One of the models predicted that a hypothetical Venusian moon at least twice as massive as Earth’s natural satellite could’ve lasted between 30 million and 1.7 billion years.

Overall, the simulations indicated that the more massive the moon, the faster it met its death. Venus is the hottest planet in the solar system, with surface temperatures of about 872 degrees Fahrenheit. That’s toasty enough to melt lead.