Scientists say if Venus ever had a moon like ours, it was doomed

Venus ' sluggish spin may be the key to why it doesn't have a moon — anymore , at least, new research says.

The study , led by University of California, Riverside astrophysicist Stephen Kane, appears in The Astrophysical Journal .

Kane's team built computer simulations of how gravity ties a planet to a moon in space , then ran Venus through them again and again.

Nearly every run ended the same way.

An ancient Venusian moon crashed onto its host planet — sometimes within 30 million years, sometimes after 1.7 billion.

At any rate, it was destined for demise.

That may crack one of the solar system's oldest cases: why Earth and Venus, near-twins in size, weight class, and composition, turned out nothing alike.

Though scientists don't yet know whether a world needs a moon to be habitable, they do know that our moon plays many crucial roles for Earth, such as steadying its tilt and controlling ocean tides.

It's not far-fetched to suppose the moon may also help keep the planet geologically active .

If Venus once had a moon but lost it, its absence could have bent the arc of that scorched world's history.

"Venus didn't require a catastrophe to arrive at what we can see today," Kane said in a statement .

SEE ALSO: Scientists knew Mercury was shrinking.

They didn't know the true extent.

The physics comes down to spin.