Shrouded in perpetual twilight, in a shadowy and frozen region of ice, the Kuiper Belt is a distant domain of icy worlds and frosty comet nuclei, circling our Sun in a weird and wonderful waltz. In this faraway Wonderland, our Sun can shine with only a faint and feeble fire, and it appears to be just another star–albeit an especially large one–swimming in a mysterious dark sea with a multitude of others of its sparkling stellar kind. Astronomers are only now first beginning to explore this cosmic wilderness, but already they have uncovered a previously hidden, secretive treasure chest filled with an abundance of strange surprises. In July 2016, an international team of astronomers announced their discovery of yet another wonder world–a new dwarf planet orbiting within the disk of icy, small worlds beyond the planet Neptune–the most distant major planet from our Sun. This newly discovered little frozen ice-world is approximately 700 kilometers in size and has one of the largest known orbits for a dwarf planet.
Designated 2015 RR245 by the International Astronomical Union’s (IAU’s) Minor Planet Center, the small world was discovered by astronomers using the Canada-France-Hawaii Telescope poised atop the dormant Mauna Kea volcano in Hawaii. The new discovery is part of the ongoing Outer Solar System Origins Survey (OSSOS).
“The icy worlds beyond Neptune trace how the giant planets formed and then moved out from the Sun. They let us piece together the history of our Solar System. But almost all of these icy worlds are painfully small and faint: it’s really exciting to find one that’s large and bright enough that we can study it in detail,” commented Dr. Michele Bannister in a July 2016 University of Hawaii Press Release. Dr. Bannister is of the University of Victoria in British Columbia, Canada, who is a postdoctoral fellow with the survey.
There are four giant planet denizens inhabiting our Sun’s family: Jupiter, Saturn, Uranus, and Neptune. Jupiter and Saturn are classified as gas-giants, while Uranus and Neptune are classified as ice-giants. The entire magnificent quartet of gigantic, gaseous worlds dwell in the outer regions of our Solar System–a domain that exists beyond the major planet Mars, and the Main Asteroid Belt that circles our Sun between the orbits of Mars and Jupiter.
The National Research Council of Canada’s Dr. J.J. Kavelaars was the first to spot 2015 RR245 in February 2016, when it revealed its distant and dim presence in OSSOS images obtained in September 2015. “There it was on the screen–this dot of light moving so slowly that it had to be at least twice as far as Neptune from the Sun,” Dr. Bannister added.
The team of astronomers became even more excited when they realized that the little ice world’s orbit carries it more than 120 times further from our Star than our Earth. The small size of 2015 RR245 is not precisely known–and its exotic surface properties need additional measurement. “It’s either small and shiny, or large and dull,” continued Dr. Bannister in the July 2016 University of Hawaii Press Release.
Distant Domain Of Icy Objects
A trans-Neptunian object (TNO) refers to any minor planet in our Solar System that circles our Sun at a greater average distance (semi-major axis) than Neptune, which is 30 astronomical units (AU) from our Sun. One AU is equal to the average distance between Earth and Sun, which is 93,000,000 miles. About a dozen minor planets with a semi-major axis greater than 150 AU and a perihelion greater than 30 AU are known. These objects are termed extreme trans-Neptunian objects (ETNOs). The term perihelion refers to the point that an object–such as a planet or an asteroid–is closest to our Sun in its orbit.
Pluto was the first TNO to be discovered back in 1930. However, it took until 1992 for the second TNO to be discovered orbiting our Sun directly, and this small frigid body was given the name 1992 QB1. As of January 2016 more than 1,750 TNOs are recorded on the Minor Planet Center’s List Of Trans-Neptunian Objects. Of these TNOs, 1,563 have a perihelion farther out than Neptune, and two hundred of these distant objects have had their orbits well enough determined to be given permanent minor planet status.
The largest known TNO is Pluto, followed by Eris, 2007 OR10, Makemake and Haumea. The Kuiper Belt, scattered disk, and Oort Cloud are three conventional divisions of this distant volume of space. However, there are variations of this particular system of classification, and a few objects such as Sedna do not easily fit into any of these three neat divisions.
Following the discovery of Pluto, many astronomers pondered the possibility that it might not be alone. The region of our Solar System called the Kuiper Belt was hypothesized to be in different forms for decades. The first to suggest the existence of TNOs was the American astronomer Frederick C. Leonard (1896-1960O. Soon after Pluto’s discovery by the American astronomer Clyde Tombaugh in 1930, Leonard considered whether it was “not likely that in Pluto there has come to light the first of a series of ultra-Neptunian bodies, the remaining members of which still await discovery but which are destined eventually to be detected”. That same year, the American astronomer Armin O. Leuschner (1868-1953) proposed that Pluto “may be one of many long-period planetary objects yet to be discovered.”
In 1943, the Irish astronomer Kenneth Edgeworth (1880-1972) proposed in the Journal of the British Astronomical Association that the material within the primeval solar nebula was too widely dispersed to coagulate into planets in the mysterious, distant, and unexplored region beyond the ice-giant Neptune. Therefore, Edgeworth suggested that this widely spaced material instead had coagulated into a mesmerizing myriad of smaller, frozen objects. Based on this, Edgeworth came to the conclusion that “the outer region of the Solar System, beyond the orbits of the planets, is occupied by a very large number of comparatively small bodies” and that, every so often, one member of this distant and frozen population of small objects “wanders from its own sphere and appears as an occasional visitor to the inner Solar System”, becoming a comet with its glowing tail flashing and thrashing across the Sun-warmed skies of the quartet of relatively small and rocky inner planets: Mercury, Venus, Earth, and Mars.
In 1951, the astronomer Gerard Kuiper speculated in an article published in the journal Astrophysics about the possibility of a similar disk having formed early in our Solar System’s evolution. Unfortunately, he did not think that such a belt could still be in existence today. This is because Kuiper was operating on the erroneous assumption common in his time that Pluto was as big as our Earth, and as a result had scattered these primordial icy bodies out toward the remote Oort Cloud that is thought to be composed of a multitude of icy comet nuclei–or, perhaps, even out of our Solar System altogether. If Kuiper had been correct, there would be no Kuiper Belt today to bear his name.
The hypothesis took many differing manifestations during the decades that followed. Additional evidence for the existence of the Kuiper Belt eventually was derived from the study of comets. Comets have finite lifespans–and this fact has been known for a very long time. As comets rampage their way inward from their frigid, frozen domain of darkness far, far away, to enter the inner kingdom where the melting warmth and glowing flames of our Star greet them mercilessly, their volatile surfaces sublimate into interplanetary space. Comets are fragile and ephermeral objects that gradually disintegrate and vanish. With each swooping approach a doomed comet makes, as it flies screaming towards our fiery Star, it loses more and more of its substance. Therefore, in order for a comet to continue to be a visible visitor from afar over the age of our 4.6 billion year old Solar System, it must be replenished frequently. One such abode of replenishment is the Oort Cloud, a still hypothetical spherical swarm of comet nuclei reaching beyond 50,000 AU from our Sun. The existence of the Oort Cloud was first proposed by the Dutch astronomer Jan Oort in 1950. The Oort Cloud is generally thought to be the birthplace of long-period comets, with orbits that last thousands of years.
However, there is a second comet population, termed short period comets, that sport orbital periods of a relatively brief 200 years. Icy, glittering short-period comets rampage through the well-lit and toasty inner Solar System from the scattered disk–a distant region linked to the Kuiper Belt. The scattered disk formed when Neptune migrated outward into the ancient, still-forming Kuiper Belt, which was then much closer to our Sun. Neptune’s migration left in its wake a population of dynamically stable objects that could not be affected by its orbit, as well as a population of objects whose perihelia remained close enough to Neptune to be jostled by that planet. Because the scattered disk is dynamically active, and the Kuiper Belt relatively stable, the scattered disk is currently thought to be the most probable place of origin for short period comets. In the distant, dark deep-freeze of the Kuiper Belt, the ice dwarf Pluto and its five moons reside along with a myriad of others of their frosty kind. This very distant domain of our Solar System is so far from Earth that astronomers have barely begun to explore it. At last, on July 14, 2015, NASA’s highly successful New Horizons spacecraft visited the Pluto system–sending back some very revealing images. New Horizons is currently flying through our Solar System’s outer limits in order to discover more secrets belonging to this faraway, faint region of icy little worlds.
Comets are really traveling, bright invaders from their kingdom of darkness and ice. These frozen objects, that are coming in from the cold, carry in their frozen and secretive hearts the most pristine of primordial ingredients that contribute to the formation of our Solar System. This very ancient mix of icy material has been preserved in the “deep-freeze” of our Solar System’s most distant and darkest domains. Comets make brilliant and beautiful spectacles of themselves when they fly into the inner Solar System, where our Earth is situated. Because comets carry these pristine elements in their frozen hearts, they serve as time capsules that can reveal some of the well-kept secrets of our Solar System’s birth and evolution. These fragile, delicate wanderers provide valuable information about the mysterious ingredients that went into the secret recipe that cooked up our Sun and its family of objects.
A New Icy World Beyond Neptune
Most of the dwarf planets, similar to 2015 RR245, were either destroyed or unceremoniously evicted from our Solar System in the violent chaos that resulted from the outward migration of the quartet of giant gaseous planets to where they now reside. The little dwarf planet 2015 RR245 is a relic–it is one of the few dwarf planets that has managed to survive to the present day. As such, it is kin to two other dwarf planets, Pluto and Eris, which are the largest known dwarf planets, as well as survivors of that ancient violent era when the giant planets made their march outward. 2015 RR245 now orbits our Star among the left-over population of tens of thousands of considerably smaller TNOs, most of which are too faint to be seen.
Exotic worlds that travel far from the heat and light of our Star possess a bizarre and rather alien geology, showing weird landscapes composed of many different frozen materials–as the recent flyby of Pluto by the New Horizons spacecraft revealed.
After spending hundreds of years further than 12 billion kilometers (80 AU) from our Sun, little 2015 RR245 is wandering towards its closest approach at 5 billion kilometers (34 AU). This small icy world will reach its closest point around 2096. 2015 RR245 has been on its highly elliptical orbit for at least the last 100 million years.
Because 2015 RR245 has only been observed for one out of the seven hundred years it requires to circle our Sun in its orbit, it is unknown where it originated and how its orbit will gradually evolve in the distant future. However, its exact orbit will be refined over the coming years, after which 2015 RR245 will be given a more colorful name. As discoverers, the OSSOS team can submit their preferred name for 2015 RR245 to the IAU for confirmation.
“OSSOS was designed to map the orbital structure of the outer Solar System to decipher its history. While not designed to efficiently detect dwarf planets, we’re delighted to have found one on such an interesting orbit,” commented Dr. Brett Gladman in the July 2016 University of Hawaii Press Release. Dr. Gladman is of the University of British Columbia in Vancouver, Canada.
2015 RR245 is the largest discovery and the only dwarf planet detected by OSSOS, which has discovered more than five hundred new TNOs. “OSSOS is only possible due to the exceptional observing capabilities of the Canada-France-Hawaii Telescope. CPHT is located at one of the best optical observing locations on Earth, is equipped with an enormous wide-field imager, and can quickly adapt its observing each night to new discoveries we made. This facility is truly world leading,” Dr. Gladman continued to note.
Earlier surveys have mapped almost all of the brighter dwarf planets. 2015 RR245 may be one of the last large worlds beyond Neptune to be detected until larger telescopes, such as the Large Synoptic Survey Telescope (LSST), come online in the mid 2020s.
OSSOS involves a collaboration of fifty scientists at institutes and universities from around the world.