PALO ALTO, CA—Astronomers at the Palo Alto Observatory are citing "lunar error" as the cause of the three-moon pileup that totalled Ganymede and severely dented Callisto and Europa Monday, causing an estimated $700 quadrillion in damage. "Apparently, a comet passed within Saturn's orbit just ahead of Callisto," Observatory associate director Charles Rayburn said, "causing Callisto to swerve and lose control, colliding with Europa and creating a pileup which Ganymede struck from behind." None of the three moons were insured.