Pluto may be a dwarf, but a planet it still is, and it has proven it can rival Mars for geological activity, if not more so. It is a world that has, does, and always will stir the imagination. Some of the mystery has been revealed, but there is still much to solve. This roundup of facts and figures will make one a pro when discussing Pluto.

Pluto was discovered by Clyde Tombaugh on February 18, 1930, at the Lowell Observatory in Flagstaff, Arizona. The discovery was announced to the world on March 13, 1930. Pluto was named by a young English girl, Venetia Burney, on May 1, 1930.

Pluto is a small world at 1473 miles in diameter. It orbits the Sun at an average distance of 3.67 billion miles and can get as close as 2.75 billion miles and as far away as 4.58 billion miles from the Sun as its orbit is highly elongated. Pluto’s orbit is inclined 17.1º off the ecliptic from the rest of the planets. It orbits the Sun once every 248.1 Earth years and a day lasts 6.39 Earth days. It is tipped 122º on its axis, even more than Uranus’ 98º leaving some regions bathed in feeble sunlight for about 100 years but then bathed in darkness for just as long.

Pluto can come within 2.65 billion miles of Earth, appear as large as 0.2 arcseconds, and shine as bright as magnitude +13.7, all of which occurred in 1989. Pluto crosses Neptune’s orbit twice bringing it closer to the Sun than Neptune for 20 years of its huge orbit. The last time this occurred was from 1979-1999. There is no danger of Pluto colliding with Neptune as it passes well above or below it at a distance no closer than one billion miles. Pluto comes 100 million miles closer to Uranus than Neptune!

The Sun is nothing more than a star as seen from Pluto’s surface but shines brightly at magnitude -18 and is bright enough to read by. Shadows on Pluto will appear sharp since the Sun’s disc closely resembles a star. Methane frost, discovered on Pluto in 1976, is altered by ultraviolet radiation from the Sun giving Pluto its pinkish-tan color.

An atmosphere was discovered around Pluto on June 9, 1988, while occulting a star. The occultation was not smooth indicating either haze layers or patchy clouds. The thin atmosphere was determined to be made up of primarily nitrogen and methane with traces of carbon monoxide and argon.

Pluto is an intensely frigid world with an average surface temperature of -387ºF and ranges between -370ºF to -400ºF but is estimated to be as cold as -420ºF during the century-long night, which is barely 40ºF above absolute zero!

Pluto has five moons consisting of one large moon, Charon, and four small moons, Nix, Hydra, Kerberos, and Styx. Charon, discovered on June 22, 1978, by James Christy, is 753 miles in diameter and orbits 12,200 miles from Pluto. The proper pronunciation is “Karen” not “Sharon”.

Charon orbits Pluto at the same rate as Pluto rotates, 6.39 days. This means that Charon is always visible on one side of Pluto and never visible on the opposite side. The same is true for Pluto in Charon’s sky. Each keeps the same face pointed at each other.

The Hubble Space Telescope discovered Nix and Hydra on May 15, 2005, Kerberos on June 28, 2011, and Styx on June 26, 2012. They are smaller than 100 miles across, irregularly shaped, orbit Pluto farther away than Charon, are visible anywhere from Pluto’s surface at any time, and do not keep the same face pointed at Pluto.

The Hubble Space Telescope produced the first direct images of Pluto and Charon confirming the contrasting bright and dark patches on Pluto and that Charon was uniformly gray. These were hinted by mutual occultations between Pluto and Charon between 1985-1990.

The idea of sending a spacecraft past Pluto began with the Voyager missions in the 1970s. Voyager 4 would have flown past Pluto on March 9, 1986, but it was never launched as the mission was scaled back to two spacecraft. Voyagers 1 & 2 were either flying too fast or headed in the wrong direction to reach Pluto. When Voyager 2 discovered nitrogen geysers on Neptune’s moon Triton in 1989, the quest to seriously send a spacecraft to Pluto began.

The New Horizons spacecraft was launched on January 19, 2006, on its journey to Pluto. It is the fastest spacecraft ever to leave Earth at 36,256 miles per hour. It was launched on a super-powerful Atlas 5 rocket that flew it past the Moon’s orbit within nine hours and past Jupiter in hardly 13 months on February 28, 2007. It flew past Pluto in just a little over nine years on July 14, 2015, at a distance of 7750 miles.

In case of failure at closest approach, New Horizons was programed to return a single, full disc image of Pluto on July 13, 2015, which ended up being the perfect image for a Valentine card as it revealed a huge, icy white heart.

A memory overload in the way New Horizons was processing all the data and commands put it into safe mode on July 4, 2015, which nearly doomed the mission only ten days before encounter. Quick thinking and teamwork corrected the problem and New Horizons was back in business on July 7. Whew!

Pluto has a huge glacier filling a deep basin that is about two miles deep, fills the western lobe of the heart and is called Sputnik Planitia. It is 400,000 square miles of frozen nitrogen coated with methane and carbon monoxide ice. The glacier has flow fields, subduction pits, hills, and dunes. The glacier is kept mobile by an underground reservoir of water ice and qualifies Pluto as an Ocean World. Pluto has bladed terrain of ice spires making up the eastern lobe of the heart. They may tower up to 1000 feet high and may be the dominant landform. The entire heart feature is called Tombaugh Regio.

Pluto has mountains up to 11,000 feet high and a pair of icy volcanoes 2½ and 3½ miles high. There is also a perfect, frozen relic of a nitrogen lake! The dark regions are not rock, but areas coated with tholins, a reddish-brown hydrocarbon caused by solar radiation interacting with methane. The mountains in these regions are snowcapped in fresh white methane frost. The dark regions reflect only 8% sunlight while the white glaciers reflect nearly 100%.

Pluto’s atmosphere is 60,000 times thinner than Earth’s. It lacks oxygen and is composed of 98% nitrogen with traces of methane, carbon monoxide, and cyanide. A haze layer extends up to 120 miles from the surface. Around 20 haze layers were seen that are no more than a mile thick. The haze appears blue, but from the surface the sky would be black, except possibly for a band of haze very close to the horizon.

Charon was once an active moon. It has moted mountains surrounded by trenches as if something flowed into them. A dark reddish polar stain probably came from methane gas escaping from Pluto.

The International Astronomical Union (IAU) may have punished Pluto like angry parents for not keeping its room clean and demoted it from planethood, but the joke is on them. Pluto is a dwarf planet; therefore, it is still a planet, and it is a world that is geologically more alive than Mercury and Mars, and it has a big heart! What is not to love?