Clyde Tombaugh: Discovering Pluto

The New Horizons Mission Sends Latest Pictures of Pluto

Pluto and its heart-shaped Tombaugh Regio for Valentine's Day. NASA/JHU-APL/SWRI/New Horizons mission

In 2015, the New Horizons mission passed by Pluto and returned images and data giving astronomers their first up-close look at a place that was only a dot in the telescope. The mission showed that Pluto is a frozen world, covered with nitrogen ice, water-ice mountains, and surrounded by a methane haze. It has five moons, the largest of which is Charon (and was discovered in 1978).

Pluto is now known as the "King of the Kuiper Belt Objects" due to its position in the Kuiper Belt. Each year people celebrate Tombaugh's birthday on February 4 and his discovery of Pluto on February 18, 1930. In honor of his discovery, the New Horizons team named a portion of the surface after Clyde Tombaugh. Future explorers may someday study (or even walk across) the Tombaugh Regio, working to figure out just how and why it formed.

Annette Tombaugh, Clyde's daughter, who lives in Las Cruces, New Mexico, noted that her dad would have been excited with the images from New Horizons. "My dad would be thrilled with New Horizons," she said.  "To actually see the planet that he had discovered and find out more about it, to get to see the moons of Pluto ... he would have been astounded. I'm sure it would have meant so much to him if he were still alive today."

Tombaugh's family members were on hand at Pluto Mission Central in Maryland in July 2015 when the spacecraft passed closest to Pluto. Along with people around the world, they watched as images came back from the distant world he glimpsed so long ago. 

Sending Clyde Tombaugh to Pluto

Clyde Tombaugh's ashes are aboard the New Horizons spacecraft, so he will get to Pluto first, along with greetings from the people of Earth. It's a long way from home, especially for the person who, as a young man, built his own telescopes from tractor parts, and taught himself all about astronomy. When he presented himself as a possible night assistant to the director of Lowell Observatory, he was snapped up and put to work on the search for Planet X — a world that astronomers suspected existed out beyond the orbit of Neptune. Tombaugh took images of the sky each night and then carefully examined them for any thing that seemed to have changed position. It was an exacting job.

The plates he used to discover Pluto are still on display at Lowell Observatory, a testament to the precise attention he paid to his work. The work he did further expanded our ideas about the solar system at the same time it made our solar system seem just a bit larger and a whole lot more complex than scientists had known before his discovery. Suddenly, there was a whole new part of the solar system to explore. Today, the outer solar system is really considered the "new frontier", where there are likely many more worlds to study. Some may be like Pluto. Others may be entirely different. 

Why Pluto?

Pluto has long caught the public imagination due to its planetary status. However, it has also been of intense interest to scientists because it's a dwarf planet and it "lives" in a very different and very distant part of the solar system than the planets. That region is called the Kuiper Belt, and beyond it lies the Oort Cloud (populated by icy chunks that are the nuclei of comets). Temperatures are quite cold there and it's occupied by an unknown number of small worlds. In addition, Pluto follows a highly eccentric orbit (that is, it doesn't orbit in the plane of the solar system). It is not the largest object "out there"—astronomers have found other, larger dwarf planets beyond Pluto. And, there may be Plutos around other stars, too.  But, our Pluto holds a special place in everyone's heart because of its discoverer.