Courtesy **Mary**There was a brief period in the history of the solar system about 3.9 billion years ago characterized by wayward space particles pelting the inner planets. The period is referred to as the Late Heavy Bombardment, and the moon still bears the crater scars of the repeated impacts (Earth was similarly battered, but the constant recycling of the crust has erased the craters).
The prevailing theory behind the LHB has long been that early reshuffling of the planets was responsible – specifically that a rebellious young Neptune moved further out from the sun (perhaps seeking a place of its own) and disturbed rocky bodies in the Kuiper Belt, causing them to “veer into the inner solar system.”
Recently, an astrophysicist at the Carnegie Institution in Washington DC has provided compelling evidence that a migrating Neptune may not have been the cause after all. He thinks that the impact craters on the moon more closely match asteroids from the Asteroid Belt just beyond Mars, and that these asteroids were sent there by a disturbed orbit of a fifth rocky planet (the other rocky planets being, of course, Mercury, Venus, Earth, and Mars).
The planet, dubbed Planet V, would probably have been bigger than the moon, but slightly smaller than Mars. The Carnegie scientist even developed a computer model detailing how Mars’ gravity could have upset V’s orbit, causing it to fall into the sun, passing through the Asteroid Belt and scattering asteroids on its way.
The theory obviously requires extensive testing before it can be accepted with any confidence, but, so far, it has passed the test of whether or not I like it. I do like it.
I’m not terribly attached to the name, though. “V” is okay, I supposed, but it’s been done. I was thinking that something along the lines of “Planet Waterslide” would be better, not only because it sounds fun, but because it more accurately describes the character of the planet as suggested by my own theories. See, I predict that further research will reveal that “V” was covered in waterslides, and inhabited solely by kittens and friendly dinosaurs (neither of whom, ironically, ever used the waterslides). Planet Waterslide was the destiny of mankind, the universe’s reward for our inevitable achievement of interplanetary travel. Unfortunately, jealous Mars, not as brave as his big brother Neptune, and who never moved out of the parents’ basement of the solar system, tricked, or possibly tripped, its little brother Waterslide.
From this point, the Carnegie theory pretty much takes over. Except that the asteroid craters on the moon, should they receive further study, will no doubt prove to be interspersed with much smaller, fluffier craters.