text: Uh. If this [i.e., big things slamming into Jupiter] is happening to Jupiter three times in thirteen months, what does that tell us about the odds of it happening to us?
  The answer is that Jupiter giveth, and Jupiter taketh away.
  In my experience, about 99% of the popular sources out there only mention the second, positive part: Jupiter is the solar system’s vacuum cleaner, hoovering up tons of wayward comets and other “small bodies” (all the way down to mere dinosaur killers) that would otherwise bomb us back into the Paleocene. The spate of recent impacts would tend to confirm that. Three cheers for Jupiter! Our hero! Let’s have a ticker tape parade!
  Barf.
  Can we all take the Jupiter worship down a couple thousand percent? Because that ain’t the whole simple story. Jupiter also giveth, and what it giveth, we don’t wanteth.
  Ever wonder why there are so many Earth-crossing asteroids? I mean, the solar system has been here for close to 5 billion years. Shouldn’t the space rocks have hit something or gotten shot out of the system by now? In fact, the vast majority of them have. Earth-crossing asteroids have orbits that are stable on multi-million year timescales… which means that on the multi-billion year timescale of the solar system, they should be history. But they’re not, because new ones keep migrating in from the asteroid belt all the time, to replenish the ones that either get flung elsewhere or (gulp) hit us. And why do new asteroids keep coming in from the belt? Because of orbital resonances with stinkin’ Jupiter. That big bully keeps throwing rocks at us!
  Now, it’s true that most near-Earth asteroids are destined to either spiral on it toward the Sun or get flung out of the inner solar system, and that only a very small fraction actually hit the Earth. And it’s also true that Jupiter sucks up a lot of comets and asteroids that might otherwise come in and hit us, and that the occasional impact damage from Earth-crossing asteroids is probably preferable to getting creamed by an unfettered rain of comets barreling in from the outer solar system. So on the balance, we’re better off with Jupiter than without. Jupiter is like that one tough guy among your childhood friends, who would keep other groups of kids from hassling your group, but might punch you really hard in the shoulder once a while, for no apparent reason.
  So let’s lay off with the fawning science news coverage and virgin sacrifices. Jupiter is nice to have around, but it is nowhere near 100% cool.
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  In other news, I took the shot at the top from my driveway the other night, shooting with a Nikon Coolpix 4500 through an Orion XT12i telescope and 13mm Stratus eyepiece. The moons from left to right are Ganymede, Io, and Europa. I could see Callisto off to the right as well, but it was out of this shot.
  Posted in Impacts, Jupiter, Photography, Planet, Shallow sky | 3 Comments »
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