After almost 10 years, New Horizons has traveled three billion miles to the Kuiper Belt to take pictures of Pluto. In 85 years, we’ve gone from this:

To this:

And I’m sure that all of you already know this, but New Horizons spacecraft was also carrying a passenger. Some of Clyde Tombaugh’s ashes traveled three billion miles as well. It’s hard for me to put in words how I feel about this. I know that Clyde isn’t alive anymore and that those ashes lack the capacity to understand the journey they’ve taken. But to me it feels like the experience of finally getting to visit somewhere you’ve only seen pictures of before, only times a billion.

Clyde Tombaugh took on the search for Pluto after the passing of Percy Lowell, of the Boston Lowells. The Lowells were a rich family and Percy was able to fund his passion for astronomy. He founded the Lowell Observatory in Flagstaff, Arizona for the express purpose of discovering a planet beyond Neptune. Up to this point, planets discovered in the outer system were found via a flawed hypothesis known as Titius-Bode Law, or Bode’s Law. Johann Titius and Johann Bode (or as I like to refer to them, “The Johanns”) theorized that the semi-major axes of each planet outward from the Sun would be roughly twice as far from the Sun as the preceding planet. The equation looks like this:

a = 4 + n, where n = 0, 3, 6, 12, 24, 48....

This equation more or less accurately predicted the positions of the known planets in the solar system, and the subsequent discoveries seemed to lend credence to the theory. Percy Lowell devoted the last decade or so of his life toward the discovery of Planet X, another gas giant whose location would have been predicted by Bode’s Law. Percy built the Lowell Observatory in furtherance of this goal, but died in 1916.


The Lowell family started the search for someone to use the observatory to continue Percy’s work, which is how Clyde Tombaugh came to be there. He was a Kansas farm boy, not even sure that he would be able to attend college due to his family’s financial circumstances. But Clyde also had a passion for astronomy. He built telescopes out of tractor parts and ground his own lenses to be able to see the stars. He had no way to photograph what he saw, but he made drawings of Mars and Jupiter and sent them to Lowell Observatory. Clyde was hired soon after.

This is the astrograph that took photographic plates of the section of space that Clyde Tombaugh was searching for Planet X. This was a painstaking process, because in order to detect planetary movement, the same bit of sky needed to be photographed at different times. Clyde then used a blink comparator to place the plates side by side, and flip through the two images looking for “wanderers.” This was where Bode’s Law failed, because while Pluto was in the general neighborhood predicted by Percy Lowell using the equation, it still took a lot of searching to find, and it turned out not to be another gas giant. When Clyde first spotted the object that turned out to be Pluto, he had to verify that it was not an asteroid, and that it had an orbit beyond that of Neptune. The discovery was official on February 18, 1930. The planetary symbol for Pluto had already been decided, a combination of the letters P and L in honor of Percy Lowell.


Pluto’s name was suggested by an eleven-year-old English girl named Venetia Burney. The name stuck because Pluto, Roman god of the underworld, possessed the power of making himself invisible - a reference to the long process of discovery. It also fit in well with the planetary symbol, incorporating Percy’s initials into the name.

After discovering Pluto, Clyde was able to fulfill his desire to attend college and graduated with a master’s degree in astronomy. He passed away in 1997, at the ripe old age of 90, not living to see the IAU re-classify Pluto as a dwarf planet.


A little part of Clyde Tombaugh got to go on a very long road trip. The container with his ashes bears the following inscription:

Interned herein are remains of American Clyde W. Tombaugh, discoverer of Pluto and the solar system’s “third zone.” Adelle and Muron’s boy, Patricia’s husband, Annette and Alden’s father, astronomer, teacher, punster, and friend: Clyde W. Tombaugh (1906-1997).