Fast, small, cheap, and putting us in touch with the outer reaches of the solar system, the New Horizons spacecraft, which will reach its closest approach to Pluto this month on July 14th, is billed by NASA as the “smart phone” of interplanetary robotic explorers. The fastest spacecraft ever launched from Earth, New Horizons is an example compact, efficient engineering opening the door to new discoveries. This month the probe, launched nearly a decade ago in January of 2006, completes its three billion mile journey, the longest journey ever to a particular object in space.
Besides the technological achievements this plucky probe represents, New Horizons is a step into a new solar system frontier, a glimpse of a region of our own planetary system where we have not yet ventured. The close look at Pluto afforded by this mission is an opportunity for the first time to study the place where the solar system gets weird. Since tiny Pluto was serendipitously discovered in 1930 by Illinois native Clyde Tombaugh, we’ve known that it didn’t quite fit with the rest of the planets. We have small, rocky planets (Mercury, Venus, Earth, and Mars) in the interior of the solar system and large, gaseous planets (Jupiter, Saturn, Uranus, Neptune) on the periphery. Pluto—usually beyond Neptune and much smaller than any other planet—is the odd man out.
Yet it’s only recently that we’ve realized Pluto isn’t alone in its strangeness. Rather, it’s the first known object from a whole new region of the solar system. This region—which is turning out to be filled with small icy objects like Pluto—is known as the Kuiper Belt, and we still don’t know much about it. We do know that Pluto was only the first dwarf planet discovered in this region. Recently Pluto has been joined by the discovery of other dwarf planets beyond Neptune like Eris, Makemake, and Huamea. New Horizons affords the first close look at this strange region of space. Once it passes Pluto, the spacecraft may be redirected to pass another Kuiper Belt object.
Besides the Kuiper Belt, Pluto is itself still an oddity. It will be the first icy planet studied closely, for instance, and may help answer the question of whether certain types of comets are simply objects like Pluto that fall into the inner solar system. Pluto also offers an example of a gravitational oddity: along with its largest moon, Charon, Pluto is technically a double planet. Pluto and Charon orbit a common center of mass between the two objects, making them unique in the solar system by forming a double planet instead of simply a planet and moon.
And then there’s Pluto’s complicated system of newly discovered moons besides Charon. Tiny Nix, Hydra, Styx, and Kerberus have recently been shown to tumble about Pluto in a chaotic system. These miniscule objects have been studied using the Hubble Space Telescope, but New Horizons will provide the first opportunity to study them up close. Indeed, the presence of Pluto’s unexpectedly complex satellite system represents one of the large unknowns of the mission: is the space around Pluto empty or filled with debris that could pose a danger to the speeding spacecraft? The weeks leading up to New Horizon’s encounter with Pluto have been a time of suspense.
New Horizons is a fly-by mission, meaning that it’s not landing on Pluto’s surface (like the Mars rovers) nor is it entering orbit around the dwarf planet (like Cassini around Saturn or Messenger around Mercury). New Horizons will study Pluto from its closest distance of about six thousand miles on July 14th while barreling past the planet at nearly forty thousand mph. It has to be moving fast—it’s had over three billion miles to cover since leaving Earth almost ten years ago.
What sort of things do scientists hope to learn from this mission? For one thing, scientists want to better understand how Pluto “fits in” with the other planets of the solar system. What do its unique properties tell us about the origins and evolution of the solar system? For the first time this month, we’ll get a close look at the strange boundary region of the solar system that we’ve only ever been able to study from afar. As far as the solar system goes, it really is “the final frontier,” and we’ll get our first close views of it this month.
This article first appeared on Friday, July 10th, 2015 in the Kankakee Daily Journal.