Mankind’s initial survey of the Solar System will be completed this month when NASA’s New Horizons space probe arrives at Pluto. Probes have visited the 8 major planets, two dwarf planets (Ceres and Vesta), and several comets and asteroids. Pluto is one of the larger members of a distant swarm called Kuiper Belt Objects (KBO), and will be the first KBO visited.
Closest approach will be on July 14, 2015. Interestingly, when New Horizons was launched on January 16, 2006, Pluto was still considered to be a “planet.” Later that same year Pluto was reclassified as a “dwarf planet” by the International Astronomical Union (IAU), a decision that is still a matter of contention in some circles. But as I explained in my September 27, 2006 post, there were several valid scientific reasons behind that decision.
The image above shows the two photographic plates Clyde Tombaugh used to discover Pluto back in January of 1930. Employing the power of the 61 cm (24″) Clark refractor at Lowell Observatory in Flagstaff, AZ, Tombaugh compared two images taken about a week apart and noticed a tiny moving point of light (circled in yellow).
It was only a featureless point, but since ...