Pluto: mysterious dot to familiar friend. Pluto is in the news lately! As the New Horizons spacecraft approaches this dwarf planet, and former ninth planet, for a high-speed fly-by on July 14, 2015 it’s timely to consider how our understanding has evolved over the last 85 years. This is how I have grown up with Pluto.
Following its discovery in 1930, by Clyde Tombaugh at Lowell Observatory, Pluto was for decades simply a dot in the sky gradually shifting position against the background stars. We knew its orbital period (its year), its distance from the Sun and could guess at its surface temperature – very cold! Every few years a new estimate of its diameter appeared in the astronomy magazines.
It was the mysterious outer planet with an odd, tilted and highly elliptical, orbit.