Pluto, the accidental planet

“Percival Lowell had carefully calculated where a planet might be, based on its effect on the orbits of Neptune and Saturn,” said Kevin Schindler of Lowell Observatory.

Tombaugh found a planet on Feb. 18, 1930, by meticulously comparing photographic slides to look for movement among the thousands of points of light.

Eventually, it turned out to be a planet too small to affect the giant planets.

“Today we know there are no perturbations. It’s a real example of a serendipitous discovery,” Schindler said.

Some of Pluto’s moons were also discovered accidentally. Jim Christy was simply trying to pin down the orbits of moons in the outer solar system when he discovered that what appeared to be the elongated axis of Pluto was actually a moon or a co-planet — Charon.

Mark Showalter was looking for dust when he found the first of his two moons of Pluto.

New Horizons scientists had just used the Hubble Space Telescope to find Nix and Hydra in 2006. Showalter thought he might find a dust ring and requested time on the Hubble.

“I did not find any rings of Pluto, but there was this extra little dot off to the side.” It was a moon he would later name Kerberos. “That was the day I became a Pluto scientist,” he said.

“A year later, there was a much larger team on the Hubble. We did not see anything on the first 12 observing sessions. The 13th was the lucky one that actually revealed Styx.”

Showalter, who was on the hazards team that gave the all-clear signal for New Horizons to proceed on its most advantageous scientific approach, was surprised and a little disappointed to not find additional moons as the spacecraft approached Pluto.

He was also relieved. New Horizons is traveling so fast that the smallest particle could do major damage.

Showalter, speaking from his post at Johns Hopkins University Applied Physics Lab last week, said he won’t breathe a sigh of relief until the flyby is completed.