Happy birthday to Pluto, discovered on this day in 1930.
Pluto, first discovered in 1930, was no more than a distant dot in our most powerful telescopes.
Moving against the backdrop of fixed stars, its orbit was constructed after years of observations, revolving like no other planet.
Pluto orbits out of the Solar System’s plane, highly inclined, and even approaches within Neptune’s orbit for a time.
In 1978, our telescopes had advanced enough to determine that it had a large satellite: the giant moon Charon.
Through occultations of distant stars, we determined Pluto had an atmosphere that changed over time, growing larger near perihelion.
1994 saw the first optically-corrected pictures of the Pluto-Charon system by Hubble, the first image to resolve these worlds independently.
By 1996, observations of Pluto led to our first-ever map of this distant world from the Kuiper belt.
In 2005, two additional moons were discovered, followed by two more in 2011 and 2012, bringing Pluto’s total to five.
Observations continued to improve, but were fundamentally limited by the great interplanetary distances.
The New Horizons mission, upon visiting Pluto, changed everything.
Flying by in 2015, its views were unlike anything else.
Pluto is the Kuiper belt’s largest world.
Celebrate its 89th anniversary in style.
Mostly Mute Monday tells the astronomical story of an object or phenomenon in images, visuals, and no more than 200 words. Talk less; smile more.
Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.