The Hidden Weights That Pull Down Spacecraft
Spacecraft circling the Moon sped up and dipped over certain places, as if something heavy lay hidden underground.
What was reported
In 1968, scientists tracking NASA's Lunar Orbiter spacecraft noticed that their orbits wobbled: over the Moon's great dark 'seas' they were pulled slightly down and forward, as though the ground beneath was heavier than it should be. They called these places mascons, for mass concentrations.
The effect was strong enough to matter. In 1972 a small satellite released by Apollo 16 into a low orbit was dragged down and crashed into the Moon about a month later.
Explanations offered
Mascons are now explained as dense rock, lava that filled great impact basins and the heavy mantle that rose beneath them, packed under the maria. Because they make most low orbits unstable, only a few 'frozen orbits' around the Moon are safe for long.
- When
- Discovered in 1968
- Where
- Beneath the Sea of Serenity, the Moon
- Witnesses
- Scientists tracking NASA's Lunar Orbiters
- Status
- Explained
Famous cases are real, widely reported events. Each file sets out what witnesses said and the explanations that have been offered, without taking a side.