Some of the smallest members of our solar system have been known since antiquity. Comets were very mysterious objects to the ancient world. They had an unusual “hairy” appearance. Unlike planets, comets seemed to follow no predictable path. They appeared at an unpredictable time, brightened and moved in unpredictable ways, and faded into oblivion. Many cultures considered comets to be omens.
On January 1, 1801, the Italian astronomer Giuseppe Piazzi discovered a new ‘planet’ in between the orbits of Mars and Jupiter. What a great way to bring in the new year! Named Ceres, this new world was far smaller than the other seven planets (Neptune had not yet been discovered). Even the most powerful telescopes of the time could not discern any sizeable disk; the object resembled a star. Piazzi initially thought that Ceres might be a comet. The central nucleus of a comet indeed looks point-like in a telescope. But Ceres was not surrounded by a coma – a cloud that typically surrounds the nucleus of a comet. Nor did it have a tail. Further observations revealed a fairly circular orbit, typical of a planet but unlike any comet.
The New Horizons mission would forever change the way we think about this little world. But in the same year that New Horizons was launched, the International Astronomical Union voted to reclassify Pluto as a dwarf planet. What exactly prompted this demotion of Pluto?
When Pluto was discovered in 1930, it was immediately accepted as the ninth planet. Seventy-six years later, the International Astronomical Union decided that Pluto should no longer be considered a planet, and reclassified it as a “dwarf planet.” What motivated this reclassification? And how exactly is a planet defined? Regardless of how we choose to classify it, Pluto is a wonderful creation and one that does not fit the secular narrative. The discovery and early investigation of this dwarf planet is a fascinating part of history.
The outermost planet of our solar system is a world of wonder and mystery. Neptune is a virtual twin to Uranus, similar in size and color. But its differences are fascinating and challenge secular thinking.