Every so often, a discovery comes along that shatters our conception of the universe.  Galileo turned his telescope to the heavens and discovered moons around Jupiter – suddenly, it was clear that Earth was not the center of everything.  Roentgen and Curie showed that matter was not entirely stable, leading to our modern understanding of physics (and the challenges that come with the harnessing of atomic energy).  Columbus sailed to find Asia; instead, he was the first to put the Americas on European maps.

Until 1958, space was believed to be a sterile place, a black void in which the planets and stars whirled.  Maybe there was an odd meteoroid or two, and far away, one might find a big cloud of gas, but otherwise space was synonymous with vacuum. 

Then Explorer 1, America's first space mission, went into orbit around the Earth.  Its particle detectors, designed to measure the free-floating electrons and cosmic rays whizzing around up there, quickly became saturated.  Girdling the planet were hellish streams of energy, particles ionized by the sun and trapped by the Earth's magnetic field. 

Overnight, our idea of space was revolutionized; a few scientists had speculated as to the existence of the "Van Allen Belts," but the idea was hardly mainstream.  More probes were sent up to determine the nature of these belts.  Pioneer 5 went beyond far into interplanetary space and sent back news of a solar atmosphere that extended far beyond the shiny yellow bits – a field of particles and rays that went beyond even Earth's orbit.  Other probes returned maps of the turbulent region where the sun's field met Earth's. 

Space was hardly empty – it was a new ocean filled with waves, eddies, and unknowns to be explored.

Yesterday, Explorer 12 zoomed into orbit, NASA's latest voyager to ply the charged sea of space.  While it practically grazes the Earth at its closest point in its orbit, at its furthest, Explorer 12 zooms out a full 50,000 miles – a fifth of the way to the Moon.  Twice every 31 hours, the satellite studies the Van Allen Belts as well as the region of cislunar space, that variable region in which the Earth and the Sun fight for magnetic dominance. 

Armed with a battery of instruments like that carried by its spiritual predecessor, Explorer 6, the new probe also has several strips of solar cells covered with varying levels of shielding.  These will help determine the extent to which the Van Allen Belts will affect ship's equipment as they travel through the deadly particles.  The data will be of particular use to Apollo astronauts on their way to the Moon.

If Explorer 1 was the satellite Columbus of the Van Allen Belts, and Explorer 6 was John Cabot, then Explorer 12 will be Amerigo Vespucci, fully determining the contours of a new ocean whose depths had been but briefly surveyed before. 

Shiver me timbers, laddie.  It's an exciting time to be a sailor!