Ferrebeekeeper has already posted about the aegis, the invulnerable shield of Jupiter/Zeus, which was fashioned by the king of the gods from the skin of his foster mother (and loaned to his favorite daughter.  However the concept of Jupiter’s shield has a larger significance.

Yesterday morning, an unknown object appears to have slammed into the planet Jupiter.  Oregon based astronomer Dan Petersen was watching the gas giant at 4:35 AM PST (September 10th, 2012) when a bright flash erupted from near the Jovian equator.  Another amateur astronomer, George Hall of Dallas, TX was filming the planet through his 12 inch telescope and recorded the flash (you can see the video here).

The September 10th, 2012 Flash on Jupiter (recorded by George Hall)

Thanks to the florid nature of science fiction entertainment, it is easy to imagine scaly green Guarillions testing out energy weapons against the huge planet, but the flash was almost certainly from a comet or asteroid striking the surface (we will know more as astronomers look at Jupiter this week).  Such impacts have proven to be much more common than imagined.

Jupiter has a mass of approximately 1.9 x 1027 kg (which is equivalent to 318 Earths).  The gas giant is 2.5 times more massive than all of the rest of the non-sun objects in the solar system added together. The sun itself comprises between 99.8% and 99.9% of the mass of the system (which should put some perspective on the precision required for our ongoing programs to scan the nearby galaxy for exoplanets).

Jupiter Relative to the Sun and the Earth (NASA Goddard Space Flight Center)

The huge mass of Jupiter (relative to other planets and moons) means that a great many asteroids, comets, meteors, and whatnot fall into its gravity well.  Were it not for Jupiter, these hazardous leftovers would otherwise fly all around the solar system willy-nilly knocking holes in things and creating unsafe conditions (just ask the poor dinosaurs about this).  The ancient myths of the Aegis provide a powerful metaphor for this protection. Jupiter does indeed provide a shield for the smaller planets:  If it did not suck up so many cosmic punches, who knows if life could even have survived?

(Lithograph by F. Heppenheimer)