Short answers, pulled from the story.
The International Astronomical Union voted to reclassify Pluto as a dwarf planet in August 2006. This decision changed the count of planets in our Solar System from nine to eight.
A planet must orbit a star, be massive enough for gravity to pull it into a round shape, and clear its orbital neighborhood of other debris. These specific conditions were established during the vote in August 2006.
Radio astronomers Aleksander Wolszczan and Dale Frail announced two planets orbiting pulsar PSR 1257+12 in early 1992. This marked the first definitive detection of exoplanets around another star.
Michel Mayor and Didier Queloz discovered 51 Pegasi b on the 6th of October 1995. It was the first confirmed exoplanet orbiting an ordinary main-sequence star.
Neptune requires 165 years to complete one revolution while Mercury takes 88 days to complete one revolution. No planet's orbit is perfectly circular as distance varies over each year between perihelion and aphelion points.