Probing the Underworld: Pluto and its Moons Quiz

Answer: New Horizons

New Horizons was launched from Cape Canaveral Air Force Station on January 19, 2006. It approached Jupiter in 2007 and the flyby gave it a gravity assist that increased its speed. On the way past, it returned data about Jupiter's atmosphere and so on. On July 14, 2015, it flew 12,500 km (7,800 mi) above the surface of Pluto, completing its flyby on October 25, 2016 and then proceeding on its secondary mission to study a number of objects in the Kuiper belt (a region of the solar system beyond the orbit of Neptune) over the next decade.

It actually experienced a software glitch caused by an overload of its primary computer on its approach to Pluto that temporarily prevented it from recording any data. Fortunately, NASA was able to resolve the problem by July 7 and it functioned as intended from then on. Furthermore, it was estimated that there was a one in 10,000 chance that debris could have destroyed the probe during the flyby before it could send any data, but fortunately this did not happen. NASA described the New Horizons flyby as fully successful in meeting its mission objectives, which were to return information about the global geology and morphology of Pluto and Charon, their atmosphere, the chemical composition of their surfaces, and so on. Additionally, the probe was able to return images of Pluto's smaller moons, providing a wealth of information about this hitherto unexplored corner of the solar system.

Answer: False

Although the discovery of several dwarf planets including Eris was a factor in its demotion, Pluto was still the largest known object in the Kuiper belt to be discovered at the time and remains so in 2021. In 2017, Pluto was estimated to be 2372 km in diameter, whereas Eris has been estimated to be slightly smaller at 2326 km. On the other hand, Eris is 27% more massive than Pluto and is believed to be the most massive object in the Kuiper belt. Both Pluto and Eris are thought to have an ocean beneath an icy crust. Although it now appears to be a cold, cold world, there is currently a theory that the interior of Pluto may have been hot when it was first formed because of radioactive decay, which some have even speculated means that its subsurface ocean may once have been habitable!

Please note that the accompanying image is an artist's impression of Eris rather than a photo. Existing photos of Eris are much more blurry!

Answer: Tombaugh Regio

The Tombaugh Regio was so-named after Clyde Tombaugh, who discovered Pluto in 1930. It is the largest bright region on Pluto and consists of two geologically distinct lobes, with the western region, known as the Sputnik Planitia, being smoother than the eastern region.

In 2020, it was found that the heart-shaped region controls the wind circulation of Pluto through processes involving the melting and evaporation of nitrogen during the day and its condensation during the night, which causes gases to move throughout the atmosphere.

Some people claim that the shape of the Tombaugh Regio resembles the Disney character Pluto, who was so-named shortly after the dwarf planet's discovery in 1930. Well, some people are certainly imaginative. The Cthulhu Macula is a dark region southwest of the Tombaugh Regio, named after the fictional monster from the works of H. P. Lovecraft. Pandemonium Dorsa is a ridge south of the Tombaugh Regio named for Pandæmonium, the capital of Hell in the poems of John Milton, while Tartarus Dorsa, on the eastern border of the Tombaugh Regio, is named for the pit of hell in Greek mythology.

Answer: Nitrogen

Although its atmosphere is tenuous, it is continuously replenished by vaporization of ices on Pluto's surface. Nitrogen is the main component, while methane makes up about 0.25% and carbon monoxide between 0.025-0.15%. Although Pluto is obviously a very cold world, it is continually bombarded by high-energy cosmic radiation, which causes these gases to react and form more complex hydrocarbons, which slowly precipitate on the surface. Additionally, these heavier compounds form layers of haze in the atmosphere, as shown in the accompanying photograph in which Pluto is backlit against the sun.

The presence of methane causes a greenhouse effect so that temperatures rise from about 60 K at the surface to a balmy 110 K (−163 °C) at an altitude of 30 km before slowly decreasing. Pluto is the only known trans-Neptunian object to have an atmosphere.

Answer: True

This is unlike the relationship between the earth and its moon, in which the moon always shows the same face to the earth, but not vice versa. This means that to an observer standing on the surface of Pluto, Charon would never seem to change position, always occupying the same part of the sky! Additionally, Pluto and Charon orbit a common centre that is located outside of Pluto itself, taking about 6.39 days each. For this reason, Pluto and Charon are sometimes considered a binary system.

When Charon was discovered in 1978 by James W. Christy, he suggested calling it Charon after his wife Charlene, whose nickname was "Char." Coincidentally, this happened to also be the name of the boatman who ferried the souls of the dead into Hades, the underworld in Greek mythology.

The name was officially accepted by the International Astronomical Union in 1985. There is some debate about its pronunciation, as the Greek name is pronounced with a "k" sound, while Christy himself pronounced the initial "ch" as a "sh" sound after his wife's name.

The former pronunciation is common among non-English speaking astronomers, while the latter is the prescribed pronunciation at NASA and of the New Horizons team.

Answer: Mordor Macula

Mordor Macula is an informal name for this area that is about 475 km in diameter. As you may have guessed, it is named after the Black Land ruled by the Dark Lord Sauron in J.R.R. Tolkien's The Lord of the Rings. A macula is a dark spot. The origin of the Mordor Macula is uncertain, although it may be a deposit of frozen gases captured from Pluto's escaping atmosphere, a large impact basin, or both. One prominent theory is that nitrogen and methane from Pluto are drawn to the cold polar regions of Charon and transformed into organic molecules by ultraviolet light.

In addition to the Mordor Macula, there is a Gallifrey Macula, named after the home world of Doctor Who. The Vulcan Planum is Charon's only plateau, located in the southern hemisphere; the Oz Terra is an extensive landmass located in the northern hemisphere.

The Kubrick Mons is the largest mountain on Charon, located in the Vulcan Planum, which, strangely enough, is surrounded by a "moat" 1-2 kilometres deep. It is named after film director Stanley Kubrick.

Answer: The outermost moon of Pluto.

Hydra was discovered by the Pluto Companion Search Team in June 2005. Its orbit is the most distant of Pluto's moons. Astronomers think that Hydra was formed closer to the surface of Pluto than it is now but moved into a more distant orbit because of tidal forces. Additionally, it was thought to have once had a more eccentric orbit, although today, its orbit is stable and nearly circular.

It has an irregular shape, being about 50.9 km long and 30.9 km wide. Hydra has water ice covering its surface that makes it highly reflective.

It was named after the nine-headed Lernaean Hydra of Greek mythology which battled Heracles and whose lair was a lake that was reputed to be an entrance to the Underworld. The nine heads of Hydra are a subtle nod to Pluto's former status as the ninth planet. Based on its name, there is now a rule that names of any features on Hydra must be related to legendary serpents and dragons from literature, mythology, and history.

Answer: Occasionally, its entire rotational axis flips.

Like the other smaller moons of Pluto, its orbit is not tidally locked and is very chaotic. In fact, it is so chaotic, that it sometimes changes the direction in which it rotates! This is caused by the changing gravitational influences of Pluto and Charon as it orbits around them. Nix has an elongated shape with dimensions of 49.8 km × 33.2 km × 31.1 km and orbits Pluto approximately every 24.86 days. Nix has an unusual reddish area about 18 km across, which may be a large impact crater where subsurface reddish material was ejected from underneath Nix's water ice layer and deposited on its surface. Like Hydra, it was discovered in June 2005 by a Hubble Space Telescope team who suspected that Pluto might have additional moons besides Charon. The names Nix and Hydra were chosen to have the same initials as New Horizons.

It was named after Nyx, the Greek goddess of darkness and night and mother of Charon. Consequently, the names of features on Nix must henceforth be related to deities of the night from literature, mythology, and history.

Answer: It is rotating sideways relative to its orbit.

Kerberos was discovered on 28 June 2011 by the Pluto Companion Search Team using the Hubble Space Telescope, who were attempting to find if Pluto had any rings. Kerberos has an odd double-lobed shape that is thought to have been formed by two smaller objects merging.

It orbits Pluto roughly every 32.17 days. Observations made by the New Horizons probe show that it is tilted about 96 degrees to its orbit, meaning that it has a sideways rotation. In Greek mythology, Cerberus is the name of a three-headed dog who guarded the entrance to the underworld.

This name was already being used for the asteroid, 1865 Cerberus, but the International Astronomical Union decided that the Greek spelling Kerberos would be acceptable as its name. There is now a rule that any names for features on Kerberos must be related to dogs from literature, mythology, and history.

Answer: Styx

Styx, the smallest known moon of Pluto, was discovered by a team led by astronomer Mark R. Showalter and announced on 11 July 2012. Observations made by the New Horizons probe show that its shape is very irregular, and it is approximately 16 km (9.9 mi) across its longest dimension.

It is thought to consist mainly of water ice and to have been formed in a collision. It orbits Pluto every 20.16 days. Its rotation is very chaotic and changes frequently. In 2013, a non-binding internet poll was held in which the public were invited to vote on its name. William Shatner, of Star Trek fame, suggested the names Vulcan and Romulus. Vulcan was actually the most popular name in the poll, but the International Astronomical Union vetoed it as the Roman god Vulcan was not associated with the underworld. Styx was the third most popular name in the poll, being the name of the most famous river in the Greek underworld and was officially announced on July 2, 2013. Acheron, Lethe, and Cocytus are names of three other rivers in Hades.