Venus May Have Devoured Its Own Moon, Astrophysicists Suggest
· Free Press Journal
Venus's lack of a moon has long puzzled scientists studying the planet closest in size and structure to Earth. A new theory presented this week offers an explanation that sounds almost like science fiction: Venus may have swallowed its own satellite whole.
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A Case of Celestial Cannibalism
According to a study published in The Astrophysical Journal by researchers at the University of California, Riverside, any moon that once orbited Venus would have been doomed by the planet's own sluggish rotation. Rather than settling into a stable orbit like Earth's moon, a Venusian satellite would have gradually spiralled inward until it was ultimately destroyed in a violent collision with its parent planet.
Lead author Stephen Krane, an astrophysicist on the project, told Reuters that such a moon "would have crashed down on the planet" within a relatively short cosmic timeframe. Computer simulations modelling the gravitational behaviour of hypothetical moons of varying sizes all pointed to the same outcome - collapse into Venus, likely within the first billion years of the solar system's roughly 4.5-billion-year history.
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The key culprit, researchers found, lies in how fast - or slow - a planet spins. Venus takes 243 Earth days to complete a single rotation, actually longer than the time it takes to orbit the sun. Earth, by comparison, spins on its axis in just 24 hours - more than 200 times faster than Venus.
This difference in rotational speed changes everything for a moon's fate. Earth's rapid spin transfers energy that gradually pushes our moon further away, causing it to drift outward at about 4 centimetres a year — a rate scientists have measured precisely using mirrors left on the lunar surface by Apollo 11 astronauts in 1969. Venus's slow rotation would have had the opposite effect, dragging any moon closer rather than letting it escape.
Rewriting an Old Planetary Mystery
Until now, scientists had largely explained Venus's moonless state in one of two ways: either the planet never captured a moon in the first place, or an early moon was destroyed in the same kind of massive impact believed to have created Earth's own satellite. Krane's team argues it's unlikely Venus escaped such a collision altogether, given how crowded and chaotic the inner solar system was during its formative years - with Venus, sitting closer to the sun, likely absorbing even more impacts than Earth.
Beyond solving a long-standing riddle, the findings feed into broader research on Venus as Earth's planetary "twin." Despite similarities in size and rocky composition, Venus today is a hostile world, trapped under a thick, toxic atmosphere that has triggered a runaway greenhouse effect, pushing surface temperatures up to 880-degree farenheit (471-degree celsius) - hot enough to melt lead. Studying how the two planets diverged, researchers say, could offer valuable clues about Earth's own long-term climate future.