Return to Newsletter Index

Planetary Ponderings - Part 9 of 9: Pluto

by Perry Pezzolanella, MVAS

Pluto is one of the final unexplored frontiers of the Solar System. Many ponder the reality of a world looming in eternal twilight, but as technology improves, Pluto has slowly yielded a few of its secrets.

  • Pluto, originally listed as the ninth planet from the Sun, orbits the Sun at an average distance 3.67 billion miles. It has a very eccentric orbit when compared to the planets as it can come within 2.75 billion miles from the Sun or as far away as 4.58 billion miles.

  • Pluto was discovered by Clyde Tombaugh on February 18, 1930 at the Lowell Observatory in Flagstaff, Arizona.

  • Pluto was the smallest planet with a diameter of 1426 miles and has three moons.

  • A day on Pluto lasts 6.36 Earth days, but its year lasts 248.1 Earth years.

  • Pluto can come within 2.65 billion miles of Earth, appear as large as 0.2 arc-seconds, and shine at magnitude +13.7 at its brightest, all of which occurred in 1989.

  • Pluto’s orbit is inclined 17.1 degrees to that of the rest of the planets.

  • Pluto’s orbit crosses Neptune twice bringing it closer to the Sun than Neptune for 20 years of it huge orbit. The last time this occurred was from 1979-1999.

  • There is no danger of Pluto colliding with Neptune as Pluto either passes above or below Neptune and no closer than 1 billion miles.

  • Pluto actually comes about 100 million miles closer to Uranus than Neptune!

  • The Sun is nothing more than a star as seen from Pluto’s surface, but it shines brightly at magnitude -18 and is bright enough to read by.

  • Methane frost was discovered on Pluto in 1976 and gives it a pinkish-tan color.

  • Pluto is like Uranus in that it is tipped way over, actually flipped over, at 122 degrees, which is even more than Uranus.

  • An atmosphere was discovered around Pluto on June 9, 1988 when it occulted a star.

  • The occultation of the star was not smooth, which is evidence of thicker haze layers or possibly even patchy clouds.

  • Pluto’s atmosphere is composed primarily of methane and nitrogen with traces of carbon monoxide and argon.

  • Pluto’s atmosphere is almost a vacuum and is temporary. It will refreeze onto the surface as Pluto moves farther away from the Sun and grows colder.

  • Pluto is an intensely frigid world with a surface temperature possibly as cold as -420 degrees F when farthest from the Sun; barely 40 degrees above absolute zero!

  • Pluto has one large moon, Charon, which was discovered on June 22, 1978 by James Christy and two smaller moons, Nix and Hydra, discovered in May 2005 by the Hubble Space Telescope.

  • Charon is 744 miles in diameter and orbits barely 12,000 miles from Pluto. Both keep the same sides facing each other.

  • 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 is never visible on the opposite side. The same is true for Pluto in Charon’s sky.

  • Charon is not pronounced "Sharon", "char on", or "car on". It is pronounced "Karen".

  • Charon is dull gray and different than Pluto’s pinkish-tan hue. This may indicate more water ice and less methane ice.

  • Eclipses of Pluto and Charon from 1985-1990 proved to be a perfect tool in determining the size of both worlds.

  • The eclipses were also useful in giving the first rough sketch of the light and dark features on both Pluto and Charon.

  • The Hubble Space Telescope produced the first direct images of surface details on Pluto and Charon, although fuzzy.V

  • The two smaller moons, Nix and Hydra, are no more than 60-100 miles across. Both moons orbit Pluto farther than Charon, do not keep the same side facing Pluto, and are visible from anywhere on the surface of Pluto.

  • A spacecraft to fly past Pluto was actually conceived a few months before the Voyager 2 flyby of Neptune in 1989 and finally launched on January 19, 2006 taking nearly 17 years!

  • The New Horizons spacecraft from launch to its flyby encounter of Pluto and Charon during July 14, 2015 is hardly more than 9 years!

  • It will be interesting to see if New Horizons discovers active geology such as geysers and active weather such as clouds and wind.

The biggest pondering of all has been whether Pluto is truly a planet. In reality, Pluto has been recently reclassified as a dwarf planet belonging to a belt of mysterious, icy, mini-worlds known as the Kuiperoids. It is most likely one of possibly thousands of the original building blocks of our Solar System.