When hunting down the origins of the solar system, it’s all in the Belt

In 1930, a 23-year-old self-taught astronomer named Clyde Tombaugh saw something move in the sky. Working for Lowell Observatory in Arizona, Tombaugh had spent the last ten months photographing tiny patches of the night sky, taking one picture of each individual location then another of the same location several days later. Using a device called a blink comparator, which could rapidly flip from one photo to the next, Tombaugh spotted an object that seemed to jump between the pictures. On March 13, 1930, Lowell Observatory announced the discovery of the dwarf plant that would later be called Pluto.

Eighty-five years later, Mr. Tombaugh will come as close to Pluto, and the mysterious band of objects around it, as any human ever has. New Horizons, a space probe launched in 2006, is set to become the first mission ever to visit the Kuiper Belt, where Pluto is the most famous resident. Equipped with an array of telescopic cameras and spectrometers as well as with one ounce of Mr. Tombaugh’s ashes, New Horizons will provide the first up close data on what NASA calls the “ancient icy mini-worlds” that exist beyond Neptune’s orbit.

The Kuiper Belt is a dark, frozen space tundra that’s home to an enormous collection of cosmic fossils. It’s a two billion mile-wide ring that wraps around our solar system, starting roughly at Neptune’s orbit and extending out to approximately fifty times the distance between the Earth and the sun. It’s a circle of space that’s theoretically packed with more than a trillion comets and hundreds of thousands of mysterious frozen bodies, many of which are estimated to date back about 4.5 billion years and may have vital information about the history of our solar system. But the number of Kuiper Belt Objects, their exact compositions, and the space weather that happens between them are all largely unknown. About 1,300 Kuiper Belt Objects have been identified in the last few decades, including the dwarf planets Haumea, Makemake, and the recently demoted Pluto, but our knowledge about what actually happens between in the Kuiper region is predominantly theoretical.

That’s mostly because of the Belt’s extreme distance from our planet and the small size of the entities within it. Even though the Kuiper Belt is absolutely huge by Earth standards—New Horizons principal investigator Alan Stern described astronomy before the discovery of the Belt as “akin to not having maps of the Earth that included the Pacific Ocean”—the moons, dwarf planets, and other bodies within the Belt are relatively tiny. Even the biggest is smaller than the United States, which makes these floating bodies difficult to spot telescopically. It also provides some context as to why the first object in the Belt wasn’t observed until 1992, even though astronomer Gerard Kuiper hypothesized the Belt’s existence about forty years prior.

It’s cold in the Kuiper Belt, as low as – 405 degrees Fahrenheit, and that frigid temperature is one of the main reasons why the Belt is so important to our understanding of the beginnings of our solar system. Most Kuiper Belt Objects are frozen through and through, with surface ices largely made of ammonia, methane, and water, the very same materials that make up comets. While many of these bodies have orbit patterns similar to those of larger planets, some have irregular orbits, probably due to Neptune’s gravitational pull. These “scattered” Kuiper Belt Objects are believed to be the early ancestors of short-period comets and may explain why approximately half of these types of comets originate within the Belt.

Aside from providing the basic ingredients for comets, the ices of Kuiper Belt Objects also serve a second important function. In the same way that cool temperatures preserve materials on Earth, the Kuiper Belt’s cold, sun-devoid conditions prevent its objects from evolving quite so fast. That means that the Belt could be comprised entirely of celestial bodies made from the building blocks of the universe, what planets like ours may have started out as before they evolved enough to support life.

Hopefully this summer will bring some answers. New Horizons is scheduled to begin a six month study of Pluto and its five moons on July 14. From there, it will head even deeper to study some of the Belt’s smaller bodies. If New Horizons completes its mission successfully, the resulting data could provide some evolutionary answers about how the solar system historically fits together and about our place within it. Plus, it will be a fitting last ride for Clyde Tombaugh.