Pluto (134340 Pluto) was the first Kuiper Belt object to be discovered in 1930, and is the biggest, and second-most massive dwarf planet known to exist in the solar system. It is also the ninth biggest, and tenth most massive object known to orbit the Sun directly. Like other known trans-Neptunian objects, Pluto consists primarily of rock and various ices, with water ice accounting for roughly one-third of the objects’ mass.
Until comparatively recently, Pluto was thought to have only one moon, but it turns out that it has five known satellites, including Charon, which is the biggest with a diameter just over 50% that of Pluto, followed by Styx, Nix, Kerberos, and Hydra. It is worth noting that since Pluto and Charon both orbit a point (barycenter) that lies outside of either body, the pair is sometimes referred to as a binary system.
Almost all of the current knowledge about Pluto and its moons only became available when the New Horizons space probe performed a brief flyby of the object in 2015. Below are ten interesting facts about New Horizons, the one and only space exploration mission of Pluto.
New Horizons had the highest launch speed to date
Dubbed the fastest spacecraft ever, New Horizons (pictured above) was launched directly into space at a speed of 16.26 km/sec (58,536 km/h; 36,373 mph), a speed that enabled it to travel directly towards Pluto without the need for one or more Earth orbits, aka gravity assists. However, solar escape velocity comes to 16.5 km/s (59,000 km/h; 37,000 mph), and this additional speed, (delta-v) was included in the final velocity of the launch vehicle.
The launch vehicles’ second stage is now in heliocentric orbit, but the third stage followed a hyperbolic escape trajectory out of the solar system and passed within 200 million km (120 million miles) of Pluto late in 2015. Nonetheless, New Horizons is not the fastest craft to leave the solar system; that honor goes to the Voyager 1 craft that left the solar system at a speed of 16.989 km/s (61,160 km/h; 38,003 mph) relative to the Sun.
First close-up view of Pluto
For various reasons, New Horizons was not meant to spend time orbiting Pluto, but to only perform a close-flyby on its way to the Kuiper Belt. The image above shows the first high-resolution, near true color image of Pluto taken by New Horizons as it was approaching the erstwhile planet.
However, New Horizons took this picture on July 13, 2015, and only reached its point of closest approach the next day, when it came to within 28,800 km (17,900 miles) of Pluto’s moon, Charon, after a journey that took 3,462 Earth days. On a scientific level, New Horizons started collecting data about five months before its closest approach, and continued collecting data for at least a month after July 14, 2015. In total, New Horizons collected more than 50 billion bytes (6.25 GB) of data, of which the last byte was received on October 25, 2016.
New Horizons’ mission objectives were many and varied
Since very little was known about Pluto and its moons, the New Horizons mission was designed to gather as much information about the system as possible in the brief time the craft was in Pluto’s vicinity. Below are the main mission objectives:
• To map the surface composition of Pluto and Charon
• To characterize the geology and morphology of Pluto and Charon
• To characterize the neutral atmosphere of Pluto and its escape rate
• To search for an atmosphere around Charon
• To map surface temperatures on Pluto and Charon
• To search for rings and additional satellites around Pluto
• To conduct similar investigations of one or more Kuiper belt objects
In fact, the amount of data gathered during the Pluto fly-by came to about 5,000 times as much data as was gathered during the Mariner missions to Mars, and it is therefore safe to say that the New Horizons mission was a resounding success.
Charon is covered with the precursors to life
Part of the detailed data collected during the fly-by revealed that Charon’s North Polar Region is covered with tholins, which are organic macromolecules that are considered to be essential for the emergence of life. In this case, the tholins are created from nitrogen, methane, and a cocktail of various other gases in Pluto’s atmosphere, and then transported/transferred to Charon, located 19,000 km (12,000 miles) away.
Pluto has a nitrogen atmosphere
Pluto has long been suspected of having an atmosphere, and New Horizon’s confirmed this when it detected a tenuous atmosphere around Pluto that consists primarily of nitrogen, and which extends several Pluto-diameters into space.
The surface coloring of Pluto (shown above) also suggests that the surface is covered with alternating patches of frozen nitrogen and methane that likely sublime when Pluto is close to the Sun, to fall back onto the surface as “snow” when Pluto recedes from the Sun.
Pluto is bigger than was thought
New Horizons settled the issue about which was the biggest dwarf planet in the solar system, Pluto or Eris. The first images of Pluto showed that Pluto is 2,370 km (1,473 miles) in diameter, as opposed to the previously accepted diameter of 2,300 km (1,437 miles). However, the increase in diameter translates into a reduced density and mass, which makes Eris the more massive of the two objects, despite Eris being marginally smaller than Pluto. In practice, the New Horizons data means that Pluto likely contains more ice than was previously thought.
Pluto has major mountain systems
While New Horizons has revealed dozens of major geological features on Pluto, very few of these features have been officially named. Thus, while there may be mountains higher than the named icy mountain range Tenzing Montes (formerly Norgay Montes), this mountain range (shown above) stands 3.4 km (2.1 mi; 11,000 ft) above the surface. This is about twice as high as the second-highest named mountain, Hillary Montes, that reaches a base-to-peak height of only 1.6 km (0.99 mile; 5,200 ft).
New Horizons is loaded with cultural artifacts
In addition to its suite of scientific instruments, New Horizons is packed with several cultural artifacts, the most notable of these being about one ounce of Clyde Tombaugh ashes, Pluto’s discoverer. Other items include a flag of the United States, a fragment of the composite material used to build the experimental suborbital spacecraft SpaceShipOne, and a USPS postage stamp featuring Pluto with the logo, “Not Yet Explored”. Other items include a collection of 434,738 names on a CD, and a quarter coin that features the state of Florida on its reverse side, and which does official duty as a weight to help trim the craft.
Although Tombaugh discovered Pluto, he did not name it. The name “Pluto” was suggested by an 11-year-old girl named Venetia Burney, in whose honor New Horizons’ dust-counting instrument was named after.
New Horizons passed up the chance to investigate Neptunian Trojans
The probe’s trajectory took it to within 180 million km (288 million miles) of Neptune’s’ trailing Lagrange Point, which was close enough for the craft to search for the suspected hundreds of Trojan moons there. While one such object, the L5 Neptune Trojan 2011 HM102, was identified as a possible target, mission controllers passed up the opportunity to observe the object because the Pluto approach was considered to be more important on the one hand, and to conserve instrument life, on the other. New Horizon’s trajectory never took it close enough to Uranus to investigate the planet and its family of satellites.
New Horizons is now heading toward Sagittarius
In November of 2016, New Horizons was 36.88 astronomical units (5.52 billion km; 3.43 billion miles) away from the Sun, and 3.83 astronomical units (573 million km; 356 million mi) away from Pluto, heading in the general direction of the constellation Sagittarius at a velocity of 14.35 km/s (8.92 mi/s; 3.03 astronomical units per year). From this distance, the probe sees the Sun at a magnitude of -18.9, while it is en route to the Kuiper Belt to investigate its next target, the minor planet designated (486958) 2014 MU69, to be followed by long-range observations of about two dozen other, yet-to be-selected Kuiper Belt objects.