The Planets

Pttm, Going Postal

Part 9 – Pluto

To give an idea of the size, the graphic below represents a view of Pluto and Charon (it’s largest moon) as they would appear if placed slightly above Earth’s surface and viewed from a great distance.  Recent measurements obtained by New Horizons indicate that Pluto has a diameter of 2370 km, 18.5% that of Earth’s, while Charon has a diameter of 1208 km, 9.5% that of Earth’s.

Pttm, Going Postal
Earth comparison with Pluto and Charon

The Prologue

Throughout this series, I would like to give a huge H/T to NASA..  I have used other sources as well, such as  and EarthSky which is a great site for showing you where to look.

I make no apology for including Pluto in this series.  As you will probably be aware, it is now classified as a “Dwarf planet”, so not a planet, but it was a proper planet throughout my childhood and most of my adult life.  So sod em.

Pictures from the Hubble telescope of Pluto are quite fuzzy as Pluto is so far away.  The New Horizons mission quite recently completed a fly-by, here is a picture of Pluto, together with its largest moon, Charon at the back.

Pttm, Going Postal


Pluto is a dwarf planet.  One of the biggest though.  It is also called a plutoid.  A plutoid is a dwarf planet that is farther out in space than the planet Neptune.  The other known plutoids are , Eris, Haumea (HOW-may-ah) and Makemake (MAH-kay-MAH-kay).

Clyde Tombaugh discovered Pluto in 1930.  He was an astronomer from the United States.  Venetia Burney named Pluto that same year.  She was an 11-year-old girl from England.

Pluto is not very big. it’s smaller than Earth’s moon.  This dwarf planet takes 248 Earth years to go around the sun.  One day on Pluto is about 6 1/2 days on Earth.

Pluto is about 40 times farther from the sun than Earth is.  It is in an area of space called the Kuiper (KY-per) Belt.  Thousands of small, icy objects like Pluto but smaller are in the Kuiper Belt.

This dwarf planet has five moons.  Its largest moon is named Charon (KAIR-ən).  Charon is about half the size of Pluto.  It has four other, much smaller, moons.  They are named Nix, Hydra, Kerberos, and Styx. They were discovered in 2005, 2005, 2011, and 2012, respectively.   All four are small being less than 100 miles (160 kilometers) wide.

Pluto is very, very cold. The temperature being -375 to -400 degrees Fahrenheit (about -226 to -240 degrees c.   Pictures from NASA’s New Horizons spacecraft show that Pluto has mountains, valleys, plains, craters, and maybe glaciers.

Pluto has about one-fifteenth the gravity of Earth. A person who weighs 100 pounds on Earth would weigh only 7 pounds on Pluto.

The high-resolution images from the New Horizons cameras show diverse ice reservoirs across Pluto’s surface.  By studying the reflected spectra from the surface, scientists have identified several different types of ices: in particular, nitrogen, methane and carbon monoxide.  The locations and characteristics of these ice reservoirs mean that there have been long epochs of ice transport across the dwarf planet’s surface.  More New Horizon pictures of Pluto are here:

The picture below from NASA’s New Horizons mission have assembled this highest-resolution color view of one of two potential cryovolcanoes (ice volcano) spotted on the surface of Pluto by the New Horizons spacecraft in July 2015, called Wright Mons.

Pttm, Going Postal

A darker veneer on top of the ices is probably tholin material – organic compounds processed by solar radiation.  These are produced slowly in Pluto’s atmosphere and gently rain down, even now, onto the surface.  An enormous darker region, informally named Cthulhu Regio, has a metres-thick layer of this organic tholin material that has built up over billions of years.  Frozen water is one of the strongest solids at the low temperatures we see on Pluto.  It is believed that the ice mountains that extend several miles above the surface are made of water ice – the biggest ice cubes in the solar system.

Most planets orbit the sun in a near-circle.  The sun is in the center of the circle.  Pluto though does not orbit in a circle!  The orbit of Pluto is shaped like an oval.  Also the sun is not in the centre as Pluto’s orbit is also tilted (See picture below).

Pttm, Going Postal

The New Horizons mission is still out there in the Keiper Belt, you can follow prgress here:

Where to find it:

To catch a glimpse of the dwarf planet, you’ll need a telescope with at least an 8-inch diameter mirror, according to the Sky conditions and Telescope.  Even at its brightest, Pluto is not visible to the naked eye and is about 27 million times fainter than Venus.  Best I can offer is this link to find it, if you have a sizeable telescope:

Check the above link regularly to see where planets and stars can currently be seen.

I do hope you have enjoyed this series, of what I hope have been a concise, yet simple series of articles about the planets in our solar system.  I leave you with this though:  Caltech researchers have found evidence suggesting there may be a “Planet X” deep in the solar system.  This hypothetical Neptune-sized planet orbits our sun in a highly elongated orbit far beyond Pluto.  The object, which the researchers have nicknamed “Planet Nine,” could have a mass about 10 times that of Earth and orbit about 20 times farther from the sun on average than Neptune.  It may take between 10,000 and 20,000 Earth years to make one full orbit around the sun.  The existence of this distant world is only theoretical at this point and no direct observation of the object nicknamed have been made.  Exciting times!

© Phil the test manager 2018