Why do we keep taking pot shots at the moon?
This started when pioneer special effects filmmaker Georges Melies poked the Man in The Moon in the eye with a Jules Vern rocket in his fanciful 1902 classic, Le Voyage Dans la Lune. Then, in 1916, rocket pioneer Robert Goddard proposed sending a rocket to the moon loaded with 15 pounds of photographic flash powder in order to record the explosion made by the impact. This was revisited in the late 1950s when the U.S. military considered the possibly of exploding a nuclear bomb on the moon just to show off to our Space Race adversaries, the Soviets.
In 2009, NASA’s Lunar CRater Observation and Sensing Satellite (LCROSS), mission sent the rocket booster’s upper stage crashing intro the lunar south pole in an experiment to excavate any trapped ice. There was some public hysteria that the impact would knock the moon into a different orbit, and bring global catastrophe. “I just want NASA to leave the moon alone. Consider it an anti-littering position,” an angry ex-Marine-turned-English teacher wrote to me. His head might have exploded if he knew that NASA deliberately crashed a 31,000-pound Saturn V rocket booster into the moon in 1971 that unleashed much more energy than the LCROSS booster, and left a nice-looking fresh crater.
In the new sci-if movie Oblivion evil space aliens destroy the Earth’s moon (photo above). This messes up our planet in completely inexplicable ways: earthquakes, volcanoes, and strange weather. Now, these aliens aren’t terribly smart because an infinitesimal fraction of all the energy it took to pulverize the moon could have been used to whack the Earth with a re-targeted asteroid.
As we learned from the dinosaur extinction that happened 65 million years ago, the impact of a celestial body a few miles across would decimate surface life.
Even worse, the moon just sits in the sky as a pile of rubble through the rest of the movie. Apparently the aliens were able to suspend Newton’s laws of gravity too — the debris would have spread out and formed a ring around Earth — a far more gravitationally attractive body.
How dependent is Earth on the moon? What if, like Venus, Earth didn’t have a large natural satellite? And what would happen if — purely hypothetically — the moon ever got obliterated by an alien superweapon? Would destroying the moon be a suitable target to wipe out, or at least cripple, life on Earth?
The Law of Attraction
Without a large natural satellite we would have no moonlit nights for romantic walks, the rhythm of the ocean tides, nor spectacular solar or lunar eclipses. We would have had no place to send astronauts during the Cold War (Mars is too far away). Human space travel might have been stuck in low Earth orbit indefinitely without that near-distance “stepping stone.”
Could life have even appeared on Earth billions of years ago without the moon? In 1993 Jeques Laskar (currently director of French National Center for Scientific Research), calculated that if Earth didn’t have a large satellite, the tilt of our axis would go very wobbly over time. Our reasonably stable tilt of 23.5 degrees gives us the seasons as the Northern and Southern Hemispheres are alternately warmed.
Our tilt does vary a little from 22 to 24.5 degrees over a 41,000-year period and this may contribute to the advance and retreat of the polar ice caps. But the consequences of a broad excursion would lead to very extreme seasons. Life would scramble to adapt and survive, and perhaps more species would go underground. Who knows, this might have led to a planet ruled by intelligent gophers, like the unnaturally strategic creature in the 1980 comedy Caddyshack.
Perhaps just as important to life is our oceans’ tidal ebb and flow. The idea is that 4 billion years ago the moon was closer to Earth and therefore tides extended several hundred miles inland. As a consequence, coastal areas saw dramatic cyclical changes in salinity and this may have enabled the formation and evolution of self-replicating molecules. However, if life first appeared deep inside Earth, perhaps at ocean floor hydrothermal vents, then lunar tides may not have offered the only route to evolution.
In 1980, John O’Keefe of NASA’s Goddard Space Flight Center proposed that Earth might have had a ring system similar to Saturn’s for a brief period. O’Keefe pointed to climatic data indicating colder winters at the end of the Eocene epoch some 34 million years ago. About this time there were showers of tektites, glassy rocks of mysterious origin. These might have rained onto Earth from a dusty ring. With a ring system, there would have been no such thing as dark nights because a brilliantly illuminated ring arc would span horizon to horizon. Life would evolve markedly differently without a nocturnal cycle, in addition to seasonal extremes. However, the moon’s tidal pull would have quickly broken apart such a ring.
In the largely forgettable 2002 remake of The Time Machine (which regrettably has very little to do with the original H.G. Wells novel), mining operations on the moon accidentally blow it up, and Earth once again gets rototilled in a screenplay. The reality is that it’s more likely that a mosquito bumping into New York’s Empire State Building would knock it over — only an object close to the mass of the moon could cause such a lunar calamity. Objects of this size no longer prowl the solar system — not even the imaginary planet Nibiru, undoubtedly home of pink unicorns, flying pigs, and Bigfoot.
Chaos theory predicts that the solar system could become gravitationally unstable at some point in the future. In 2009, Laskar ran computer simulations of orbital instabilities over the next five billion years. The result is that in 25 out of 2501 simulations, the orbits of the planets were severely disrupted. This means there is a very small but finite chance that Mars could eventually come careening near us and possibly collide with the moon.
Based on evidence from the Apollo lunar samples, planetary astronomer Bill Hartman developed the hypothesis in the 1970s that the moon was born out of just such of a cataclysmic collision 4.4 billion years ago when Earth collided with a Mars-sized body. Models developed by Robin Canup of the university of Colorado show how some of the the ejected debris coalesced to form the moon.
Peter Ward and Don Brownlee have used this to build their Rare Earth Hypothesis: that Earth might be the only planet, anywhere, suitable for intelligent life to evolve. However, NASA’s Spitzer space telescope and other observatories now show that a lot of planetary bumping and grinding goes on around young stars, as evident in the circumstellar disks of dust from protoplanets. Impact-born satellites may be common. If so, extraterrestrial civilizations may share our romance for eclipses, tides, and moonlight walks that are possible on their worlds too.
Therefore, they’d never have the heart to blow up our moon.
Image credits: Universal Pictures, D. Agular, NASA/T. Tucciarone