In the distant, unimaginably cold outer limits of our Solar System, strange, alien frozen objects, such as the ice dwarf planet Pluto, circle our Star, the Sun, whose lovely stellar light can shine through the darkness of interplanetary space with only a faint and feeble fire. On July 14, 2015, after a decade-long incredible and treacherous journey through the shadowy, cold twilight of the space between planets, belovedatmosphere NASA’s heroic New Horizons spacecraft triumphantly made its historic closest approach to Pluto, at about 7,750 miles above its well-hidden surface–making it the very first space mission to reach and explore a world so extremely far from Earth. In September 2015, New Horizons astronomers released new, bizarre, and wonderful images of Pluto that were taken by the New Horizons spacecraft, and these incredible pictures reveal a bewildering, bewitching variety of features on the surface of this small icy world that caused mission scientists to wonder at their complexity, as they observed the unique features of this remote, geekstyleguide beloved, little world, that inhabits the dark deep-freeze of the outermost fringe of our Star’s family.
“Pluto is showing us a diversity of landforms and complexity of processes that rival anything we’ve seen in the Solar System. If an artist had painted this Pluto before our flyby, I probably would have called it over the top–but that’s what is actually there,” Dr. Alan Stern commented in a September 10, 2015 Johns Hopkins University Applied Physics Laboratory (JHUAPL) Press Release. Dr. Stern, of the Southwest Research Institute (SwRI) in Boulder, Colorado, is New Horizons Principal Investigator.
The New Horizons spacecraft has now passed Pluto, after its decade-long journey through our Solar System. New Horizons made its closest pass by Pluto on the morning of July 11, 2015, almost 8,000 miles above its strange and alien icy surface.
The Pluto story began in the 1930s when the young American astronomer Clyde Tombaugh (1906-1997) was given the difficult job of searching for the elusive, hungryhikers and probably non-existent, Planet X. Planet X is a mysterious, secretive, large major planet that some astronomers think haunts the frigid darkness beyond the orbit of Neptune–the farthest known major planet from our Star. Tombaugh, indeed, did hit pay dirt when he spotted a very dim and distant point of light–although it was not the long-sought Planet X. That little point of light was Pluto–a complex and bewitching diminutive frozen world.
The New Horizon’s July 2015 flyby of the ice dwarf planet and its quintet of icy moons is providing a close-up view of our Solar System’s Kuiper Belt, a distant region in the outer limits of our Sun’s family. This highly successful spacecraft, soaring into a new frontier in space, will help astronomers attain a better understanding of the origins of our Solar System. The remote Kuiper Belt is the distant home of a multitude of somersaulting icy objects that range in size from boulders to dwarf planets–like Pluto. Kuiper Belt Objects (KBOs), stickyspatula such as Pluto, preserve in a kind of deep-freeze, important information about the ancient birth of our Solar System.
Distant, dark, and mysterious, the Kuiper Belt is situated far beyond the deep blue, banded, gaseous ice-giant, Neptune. Astronomers are now first beginning to explore this distant frontier, where trillions of sparking, icy objects dance around our Sun. Pluto is a relatively large inhabitant of the Kuiper Belt, and it was classified as the ninth major planet from our Sun after its discovery. However, with an increased understanding among astronomers that this intriguing, distant, frigid ball of ice and rock is only one of a number of other, similar, relatively large frozen worlds dwelling in the Kuiper Belt, the International Astronomical Union (IAU) was prompted to formally define the somewhat controversial term “planet” in 2006–and unlucky little Pluto lost its lofty classification as the ninth major planet inhabiting our Solar System. Now, re-classified as merely a dwarf planet, this beloved small world remains an object of considerable affection, mystery, and sometimes heated controversy among members of the astronomical community who are still trying to come up with an acceptable definition of precisely what a “planet” is.
Pluto has five known moons: Charon, Nix, Hydra, Kerberos, and Styx. Charon is by far the largest of this enchanting icy quintet of moons, and it possesses a diameter about 50% that of Pluto. The demoted, unlucky little world that is Pluto was named for the Roman god of the underworld. Charon was discovered in 1978 by the American astronomer James Christy.
For most of the 20th century, astronomers generally believed that Pluto was an isolated, icy world dwelling in the distant darkness of the outer realm of our Solar System–far from the welcome warmth and comforting light of our Star. However, in 1992, the very first KBO (other than Pluto and Charon) was spotted, and astronomers then realized that Pluto is not really as far away from the madding crowd of other similar frozen objects, haunting the distant Kuiper Belt, as previously thought. Another KBO, Eris, was discovered in 2005, and it proved to be a bit more massive than Pluto.
Since 1992, a significant number of other little icy worlds akin to Pluto–displaying similar eccentric orbits–have been discovered. Pluto shows a highly inclined and eccentric orbit that carries it from 20 to 49 Astronomical Units (AU) from our Star. One AU is equal to the average separation between Earth and Sun, which is about 93,000,000 miles.
Dr. Stern explained in the Fall 2015 issue of Ad Astra, a publication of the National Space Society, that “The entire Pluto system is tipped on its side, like the planet Uranus, and in its current geometry some of the planet is in permanent solar shadow. The same is true for Charon.”
New Horizons was launched on January 19, 2006, embarking on a ten-year, three-billion-mile treacherous journey to our Solar System’s previously unexplored, remote outer limits.
A Bewildering, Beloved, And Complicated Icy World
New Horizons began a year-long download of new images and other data over the Labor Day weekend in 2015. Images then downlinked more than doubled the amount of Pluto’s mysterious surface observed at resolutions as good as 440 yards per pixel. The images unveil new features that are as diverse as possible dunes, nitrogen ice flows that are thought to have oozed out of mountainous areas down onto plains, and even networks of valleys that may have been carved by material flowing over Pluto’s surface. They also show large regions that resemble the chaos terrains observed on Europa, one of Jupiter’s four large Galilean moons. Pluto displays similar chaotically jumbled mountains.
“The surface of Pluto is every bit as complex as that of Mars. The randomly jumbled mountains might be huge blocks of hard water ice floating within a vast, denser, toybender softer deposit of frozen nitrogen within the region informally named Sputnik Planum,” explained Dr. Jeff Moore in the September 10, 2015 JHUAPL Press Release. Dr. Moore is leader of the New Horizons Geology, Geophysics, and Imaging (GGI) team at NASA’s Ames Research Center in Mountain Field, California.
The images also unveiled, to the prying eyes of curious astronomers, the most heavily cratered–and therefore oldest–terrain yet observed by New Horizons on Pluto. This old, cratered terrain is interestingly situated next to the most crater-free–and therefore youngest–icy plains. Heavily cratered surfaces indicate an old surface, while relatively crater-free surfaces indicate a young surface rendered smooth by resurfacing that erases older craters.
There might even be a field of wind-blown, dark dunes on Pluto, among some other intriguingly weird possibilities. “Seeing dunes on Pluto–if that is what they are–would be completely wild, because Pluto’s atmosphere today is so thin. Either Pluto had a thicker atmosphere in the past, or some process we haven’t figured out is at work. It’s a head-scratcher,” Dr. William B. McKinnon told the press on September 10, 2015. Dr. McKinnon, a GGI deputy lead, is of Washington University in St. Louis, Missouri.
The images also show that Pluto’s global atmospheric haze has considerably more layers than astronomers realized, and that the haze creates a strange and mystifying twilight effect that gently lights up the nightside terrain close to sunset, making them fortuitously visible to the prying eyes of New Horizons.