Credit: By C m handler (Own work) [CC BY-SA 3.0 (httpcreativecommons.orglicensesby-sa3.0) or GFDL (httpwww.gnu.orgcopyleftfdl.html)], via Wikimedia Commons

"Pluto" by C.M. Handler - Artistic impression based

on Hubble Space Telescope generated images

On July 14th the mysterious dwarf planet Pluto will finally give up many of its secrets. On that date the New Horizons spacecraft, after a trip lasting nearly a decade, is scheduled to fly within 8,000 miles of it. It was first discovered by Clyde Tombaugh in 1930 at the Lowell Observatory in Flagstaff, Arizona. Up until now its location at 39 times Earth’s distance from the sun and its atmosphere have kept its secrets safe. Little is known about Pluto except for its tilted orbit at about 17 degrees to the plane of the ecliptic; its small size; and an atmosphere of nitrogen, methane and carbon monoxide. In fact, during 85 years of observation its estimated mass has continued to diminish until it shrank itself completely out of planethood. In 2006 it became a dwarf planet.

During the coldest part of Pluto’s year, which lasts 247.7 Earth years, its atmosphere exists as frozen ices on its surface. Temperatures approach minus 400 degrees Fahrenheit (minus 240 degrees Celsius). When its orbit approaches the sun the dwarf’s temperature reaches a balmy minus 369 degrees Fahrenheit (minus 222.78 degrees Celsius). The ices vaporize to form an atmosphere until it once again moves farther from the sun. (The coldest temperature recorded on Earth was about minus 130 degrees Fahrenheit.)

 Pluto’s moon, Charon, discovered in 1978, is almost half the size of Pluto. By studying the interaction of the two bodies scientists have determined that Pluto’s mass is only two-thousandths that of Earth. Because of their relative size Pluto and Charon form a binary system that revolves around a common point in space, complicated by the existence of at least four more smaller moons. The discovery of even more moons could make the interaction of all these tiny bodies weird indeed.

Pluto/Charon System
Credit: "ESO - Pluto-Charon system (by)" by ESO - Pluto-Charon system. Licensed under CC BY 4.0 via Wikimedia Commons -

Artist's impression of the Pluto/Charon system

The New Horizon spacecraft has entered the most hazardous part of its journey as it nears its goal. Pluto lies in the closest part of the Kuiper Belt, a place of hidden moons and deadly cosmic dust. The smallest particle of sand can destroy a computer processing unit or disable an electrical component. Scientists have planned alternate trajectories in case they discover such menaces but changing the spacecraft’s flight would mean a great loss to science.

Plutonic Trivia

1.  The Day

The sun rises in the west and sets in the east, approximately once every 6.4 Earth days.

2.  Why Pluto was demoted to Dwarf Status

The International Astronomical Union defines a planet as being round, orbiting the sun and having sufficient gravitational power to clear its orbit of most debris. Pluto fails the last requirement. It is only two-thirds the size of our moon. Placed side by side, almost three systems consisting of Pluto and its five known moons would fit between the Earth and its moon. 

Size Comparison: Earth, Moon, Pluto, Charon
Credit: "Pluto Charon Moon Earth Comparison". Licensed under Public Domain via Wikimedia Commons -

Size comparison of Earth, its moon, Pluto and Charon

3.  Cosmic Census

In addition to discovering Pluto in 1930, Clyde Tombaugh found other celestial objects while studying photographic plates of the sky: 29,500 galaxies, almost 4,000 asteroids (775 of them new) and a new comet.

4.  New Horizon’s “Passengers”

The New Horizon spacecraft’s payload includes a vial of Tombaugh’s ashes, two U.S. flags, a postage stamp bearing the unintentionally ironic phrase “Pluto: Not Yet Explored,” and a Florida state quarter, given to New Horizon principal investigator Alan Stern by then Governor Jeb Bush.

5.  It Doesn’t Take a Scientist to Name a Planet

Eleven-year-old English Venetia Burney casually suggested calling the new planet “Pluto” at breakfast. She wasn’t the first in her family to name an astronomical body. Her great-uncle Henry Madan named the Martian moons Phobos and Deimos (Fear and Terror, appropriate names for the attendants of Mars.). Venetia couldn’t tolerate people thinking she had named the planet after Disney’s hound. Though the dog did first appear in 1930 it didn’t acquire the name until May 1, 1931.

6.  Stopped up

The naming of Pluto was temporarily delayed because of an American laxative called Pluto Water which pledged, “When nature won’t, Pluto will.”

7.  Faster Than a Speeding Bullet

The New Horizon spacecraft got a gravitational boost in 2007 when it passed Jupiter. The giant planet slung it on to a speed of 51,000 miles per hour. That’s plenty of velocity to speed it past Pluto, through the Kuiper belt and far beyond.

If the Mission Succeeds…

Team members aren’t sure what they will discover if New Horizon reaches its goal. Blurry Hubble images have shown very dark and very bright patches on Pluto which may indicate the existence of organic chemicals smearing the icy surface. Scientists will not be surprised if they see signs of volcanic activity on both Pluto and Charon, similar to that on Triton, Neptune’s largest moon.

After 85 years scientists will finally get to investigate Tombaugh’s mysterious little world close hand. In a symbolic way, because of the vial of his ashes making the trip, Clyde will too. And who knows what worlds this stalwart little spacecraft, about the size of a piano, will find deeper in the Kuiper Belt and beyond.

New Horizons Pluto fly-by
Credit: By NASA/JHU APL/SwRI/Steve Gribben [Public domain], via Wikimedia Commons

Artist's conception of the New Horizons fly-by of Pluto by Steve Gribben for NASA