The destruction of the Moon is a hypothetical global catastrophe scenario explored in fiction [1] and, informally, by scientists.
Completely destroying the Moon to avoid the debris reassembling into a satellite would require an amount of energy larger than the Moon gravitational binding energy, estimated to be 1.2 × 1029 J. [2] [3] [4] This equals a bit less than 600 billion 50-megaton nuclear bombs, such as the Tsar Bomba, [5] [4] [2] [6] roughly equivalent to the full energy output by the Sun in six minutes. [4] For comparison, the impact that created the South Pole-Aitken basin, the largest lunar impact structure, had an energy of roughly 4 × 1026 J, 300 times smaller. [7] Bringing the Moon's orbit within the Roche limit of Earth (within about 18,000 km (11,000 mi)) would also destroy it. [3]
Without the Moon, tides would still happen—the Sun's gravity also causes tides—but they would be substantially reduced, [8] a quarter of the size of the current spring tide. [9] The sudden disappearance of the Moon however could release water pressure and create large potentially catastrophic waves around the oceans. [8] The reduction of tides could have profound negative consequences on coastal ecosystems. [10] Tides also help to drive ocean currents; without the Moon, weather extremes and major weather events would be more common. [10]
In 1993 numerical simulations suggested that the Moon is necessary to keep the Earth's axial tilt stable. Without the Moon the axial tilt of Earth could therefore oscillate chaotically from 0° to 45° on the scale of tens of thousands of years, possibly reaching 85° on timescales of several million years, [11] with severe climatic consequences. [9] [4] [6] More recent studies however suggested that, even without the Moon, Earth's axial tilt could be relatively stable on the scale of hundreds of millions of years. [12] Without the Moon, neither solar nor lunar eclipses would exist. [9]
Violent destruction of the Moon would likely bring substantial debris to impact Earth. Such debris would be slower, and thus each debris fragment have only about 1% of the kinetic energy with respect to an asteroid of the same size, therefore their impact would be less destructive. [9] However, their sheer quantity could lead nonetheless to substantial atmospheric heating, possibly leading to extinction of life on Earth. [4] [6] The mathematician and Usenet personality Alexander Abian proposed that the destruction of the Moon would stabilize seasons and eliminate natural disasters from Earth. [13] Apart from being practically unfeasible, [5] Abian's claims have no scientific basis— destroying the moon would actually cause natural disasters. [8]
Natural satellites can and do get destroyed. The rings of Saturn possibly originated from the destruction of a former moon, called Chrysalis. [14] The capture of Triton by Neptune possibly destroyed some of the previous moons of Neptune, by crashing them on Neptune or Triton itself. [15] [16] In turn, tidal interactions also cause Triton's orbit, which is already closer to Neptune than the Moon is to Earth, to gradually decay further; predictions are that 3.6 billion years from now, Triton will pass within Neptune's Roche limit and be destroyed. [17] The Mars moon Phobos is expected to meet a similar fate. [18] Phobos gets closer to Mars by about 2 cm per year, and it is predicted that within 30 to 50 million years it will either collide with the planet or break up into a planetary ring. [19] Outside the Solar System, exomoons might collide with planets, removing life from them. [20]