BBC - Scientists have come up with a surprising new theory about one of our neighbouring planets - and it involves a missing moon.
They think Venus may once have had one, but that it slowly moved closer to the planet, before eventually crashing into it.
The idea could help explain why Venus doesn't have a moon today, although experts can't say for sure that one ever definitely existed.
So, what could have happened? Keep reading to find out.
The research was carried out by scientists at the University of California, Riverside, in the US.