In the distant perpetual twilight of the deep-freeze of our Solar System, a multitude of sparkling icy objects–both large and small–circle our Sun beyond the orbit of the giant, gaseous, and beautiful blue planet Neptune, which is the outermost of the eight major planets from our Sun. Here, in the mysterious and frigid Kuiper Belt, our Sun appears to be only a particularly large star shining brightly, like a celestial firefly, in the midst of a swarm of smaller stars. On July 14, 2015, after spending ten treacherous years soaring through interplanetary space to reach its primary destination in the Kuiper Belt–the ice-dwarf-planet Pluto and its quintet of little moons–NASA’s New Horizons spacecraft successfully made its historic closest approach to the Pluto system. Images sent back to Earth revealed new and exciting secrets long held by this beloved little world with a big heart. But, New Horizons’ voyage through our Solar System’s outer limits is far from over as it speeds toward yet another denizen of the Kuiper Belt, 2014 MU69. In October 2016, planetary scientists reported that this tiny ice-world, lurking secretively a billion miles beyond Pluto and its moons, is red–very, very red!
Indeed, this distant little worldlet far, far away may be even redder than Pluto! Data obtained from the Hubble Space Telescope (HST), provided the first enticing hints of the strange nature of the surface properties sported by tiny 2014 MU69 that New Horizons is scheduled to survey on January 1, 2019.
Mission scientists talked about this as well as other Pluto and Kuiper Belt discoveries in October 2016 at the American Astronomical Society’s (AAS) Division for Planetary Sciences (DPS) meeting, held jointly with the European Planetary Science Congress (EPSC) in Pasadena, California.
“We’re excited about the exploration ahead for New Horizons, and also about what we are still discovering from Pluto flyby data. Now, with our spacecraft transmitting the last of its data from last summer’s flight through the Pluto system, we know that the next great exploration of Pluto will require another mission to be sent there,” Dr. Alan Stern told the press at the meeting. Dr. Stern, who is of the Southwest Research Institute in Boulder, Colorado, is the New Horizons mission’s principal investigator.
Dr. Stern continued to note that Pluto’s complex and layered atmosphere is hazy and seems to be almost entirely free of clouds in images taken with New Horizons’ cameras. “If there are clouds, it would mean the weather on Pluto is even more complex than we imagined,” he added.
Denizens Of The Outer Limits
Pluto was discovered almost a century ago when a young farmer’s son from Kansas, the astronomer Clyde Tombaugh (1906-1997), was given the difficult assignment of hunting for the elusive–and possibly non-existent—Planet X. According to theory, Planet X is a giant planet hiding out somewhere in the distant darkness beyond Neptune. While using a telescope in Flagstaff, Arizona, to aid him in his quest, Tombaugh did manage to discover a very small dim dab of light that eventually proved to be the interesting icy “oddball” that is now known as Pluto–instead of the targeted Planet X.
For most of the 20th century, astronomers thought that Pluto was a solitary little world where it is situated in the outer regions of our Solar System. However, in 1992, the discovery of another Kuiper Belt Object (KBO) inhabiting this region–other than Pluto and its largest moon Charon–forced planetary scientists to come to the realization that Pluto is not solitary at all, but circles our Star in the company of a multitude of others of its distant, frozen kind. Since 1992, a myriad of other icy and rocky small worlds, very much like Pluto, have been discovered by astronomers on the hunt for these remote objects. Indeed, some recently discovered distant denizens of our Solar System’s deep freeze also circle our Sun in eccentric orbits–just like Pluto. The dwarf planet Eris is the most important of these more recently detected scattered disc objects. Discovered in 2005, Eris is slightly more massive than Pluto, and its discovery eventually resulted in the scientific realization that Pluto is just one of many. As a result, poor little Pluto was unceremoniously booted out of the pantheon of major planets. It had formerly been designated the ninth major planet from our Star ever since Tombaugh discovered it in 1930. The scattered disc is a distant circumstellar disc in our Solar System that hosts a sparse population of icy dwarf planets. The innermost region of the scattered disc overlaps with the Kuiper Belt.
In 2006, the International Astronomical Union (IAU), was forced to define the term “planet”, and this resulted in the demotion of Pluto to mere dwarf planet status. Nevertheless, this very remote frozen world, with a big icy heart, remains an object of great affection–as well as debate among members of the planetary science community still trying to come to terms with the need for a more precise definition of what a “planet” actually is.
Pluto, like other KBOs, is generally thought to be composed mainly of a combination of ice and rock. It also sports a highly eccentric and inclined orbit that takes it from 20 to 49 astronomical units from our Star. One AU is equivalent to the average distance between Earth and Sun, which is about 93,000,000 miles. Pluto periodically wanders towards our Star at a closer distance than Neptune. However, this is not a sign of impending catastrophe. This is because an orbital resonance with Neptune successfully prevents the two worlds from meeting their doom in a smash-up of cosmic proportions.
The Kuiper Belt reaches out from the orbit of Neptune to approximately 50 AU. Neptune’s average distance from our Sun is approximately 30.1 AU–its perihelion (when it travels closest to our Star) is 29.8 AU, while its aphelion (when it travels the furthest from our Star) is 30.4 AU.
2014 MU69 was discovered on June 26, 2014 during a preliminary survey by astronomers using the HST to determine a suitable KBO for the next flyby (after the Pluto system) by the traveling New Horizons spacecraft. This discovery demanded the use of the HST, because with an apparent magnitude of only 26, 2014 MU69 is much too dim to be seen–except by the most powerful of telescopes. The HST is also able to conduct very precise astrometry and, as a result, can provide a reliable orbit determination.
At first, 2014 MU69 was dubbed 1110113Y, and it was given the nickname “11”, for short. The object’s official name, 2014 MU69, was chosen by the Minor Planet Center (MPC) in March 2015 after sufficient orbital information had been obtained. 2014 MU69’s potential as the second KBO target for the New Horizons probe was announced by NASA in October 2014.
Based on its distance and brightness, 2014 MU69 is estimated to sport a diameter of 20 to 30 miles. The KBO’s orbital period is approximately 293 years and it has a low inclination and low eccentricity. This unperturbed orbit indicates that it is a frigid classical KBO which has probably not experienced much in the way of significant jostling. Also, observations conducted in May and July 2015 significantly reduced the uncertainties in the KBO’s orbit.
Having finished its primary mission of a flyby of Pluto and its moons, the New Horizons spacecraft was maneuvered for a flyby of 2014 MU69 which is to occur on December 31 2018 or January 1 2019. At this point, New Horizons will be about 434.4 AU from our Sun in the constellation Sagittarius. 2014 MU69 is the first object to be targeted for a flyby that was discovered after the spacecraft had been launched.
Destination: A Small Red World Beyond Pluto
Astronomers were already aware from previous telescope observations that Pluto’s alien icy surface beneath its atmosphere experienced substantial variations in brightness. Data derived from New Horizons’ Pluto flyby confirmed those earlier observations, and also revealed that the brightest regions (such as those within Pluto’s icy heart-shaped feature) are among the most reflective, bright areas in our entire Solar System.
“That brightness indicates surface activity. Because we see a pattern of high surface reflectivity equating to activity, we can infer that the dwarf planet Eris, which is known to be highly reflective, is also likely to be active,” explained Dr. Bonnie Buratti in an October 18, 2016 NASA Jet Propulsion Laboratory (JPL) Press Release. Dr. Buratti is a science team co-investigator from the JPL, which is in Pasadena, California.
While Pluto displays many varying types of activity, landslides apparently do not occur on its icy surface. In contrast, landslides have been detected on Pluto’s large moon, Charon. Charon itself is about 750 miles across, which makes it almost half the size of Pluto.
“We’ve seen similar landslides on other rocky and icy planets, such as Mars and Saturn’s moon Iapetus, but these are the first landslides we’ve seen this far from the Sun, in the Kuiper Belt. The big question is will they be detected elsewhere in the Kuiper Belt,” noted Dr. Ross Beyer in the October 18, 2016 JPL Press Release. Dr. Beyer is a science team researcher from the Sagan Center at the SETI Institute and NASA’s Ames Research Center, both in Mountain View, California.
Both HST and cameras aboard the New Horizons spacecraft have been targeting KBOs since 2014, with New Horizons making good use of its unique vantage point as it soars through the Kuiper Belt to observe nearly a dozen small worlds in this barely explored portion of our Solar System’s outer limits. 2014 MU69 is the smallest KBO so far to have its color determined. Planetary scientists have used this new information to confirm the object as a denizen of what is termed the cold classical region of the Kuiper Belt, which is believed to play host to some of the most ancient and primordial material in our entire Solar System. Here, in our Solar System’s distant deep freeze, the original material that went into the formation of our Solar System has been preserved. Therefore, this material can serve the function of a frozen time capsule, revealing wonderful long-lost secrets from the distant past about how our Sun and its family of objects–including our Earth–were born.
New Horizons post-doctoral researcher, Dr. Amanda Zangari, from the Southwest Research Institute, told the press on October 18, 2016 that “The reddish color tells us the type of Kuiper Belt object 2014 MU69 is. The data confirms that on New Year’s Day 2019, New Horizons will be looking at one of the ancient building blocks of the planets.”
New Horizons is now soaring away from our Sun at about nine miles per second, on its way to the mysterious distant realm of frigid and perpetual twilight in our Solar System’s outer limits–and the Wonderland of brave new worlds that do their sparkling dance within it.