Pluto and its largest moon, Charon. NASA’s New Horizons spacecraft, Public domain

Pluto Quiz

How Well Do You Know the Dwarf Planet?

Are you fascinated by the mysteries of our solar system? Put your knowledge to the test with this quiz focused on Pluto and its intriguing moons.

Discover if you're a true space enthusiast ready to navigate through the facts and myths surrounding this distant world.

Start the Pluto Quiz

Questions and answers about Pluto

• Why was Pluto reclassified as a dwarf planet?

  Pluto was reclassified as a dwarf planet in 2006 by the International Astronomical Union (IAU). This reclassification was due to the establishment of three criteria that a celestial body must meet to be considered a planet: it must orbit the Sun, be spherical due to its own gravity, and have cleared its orbital neighborhood of other debris. While Pluto meets the first two criteria, it does not meet the third because it shares its orbital zone with objects in the Kuiper Belt, an area of the solar system filled with icy bodies and remnants from the solar system's formation. Therefore, Pluto was reclassified as a dwarf planet, recognizing its unique characteristics that differentiate it from the larger planets in our solar system.

  • Because it does not clear its orbital neighborhood of other debris, sharing its orbit with objects in the Kuiper Belt.
  • Due to its small size, making it smaller than some of the moons in the solar system.
  • Because it was discovered to be a moon of Neptune, rather than a standalone planet.
  • Due to its distance from the Sun, being far removed from the main planetary zone of the solar system.

• What is the largest moon of Pluto?

  The largest moon of Pluto is Charon. Discovered in 1978, Charon is the largest and closest of Pluto's five known moons. Notably, Charon is about half the size of Pluto itself, making the Pluto-Charon system more of a double dwarf planet system than a typical planet-moon system. This size similarity leads to a unique gravitational interaction between the two, causing them to orbit a point in space outside of Pluto's surface, known as the barycenter. The other four smaller moons of Pluto are Nix, Hydra, Kerberos, and Styx.

  • Charon, with almost half the size of Pluto.
  • Nix, a small moon discovered much later than Charon and known for its irregular shape.
  • Hydra, the outermost moon of Pluto, known for its highly reflective surface.
  • Pluto does not have any moons; it was once mistakenly believed to have one large moon.

• How long does it take Pluto to orbit the Sun?

  Pluto takes about 248 Earth years to complete one orbit around the Sun. This long orbital period is due to its great distance from the Sun, averaging about 5.9 billion kilometers (3.7 billion miles) away. Pluto's orbit is also highly elliptical, meaning its distance from the Sun varies greatly throughout its year. At its closest approach (perihelion), Pluto comes nearer to the Sun than Neptune, but at its farthest (aphelion), it ventures much farther out into the Kuiper Belt. This unique orbit contributes to the significant variations in its surface temperature and solar energy received.

  • About 248 Earth years, due its great distance from the Sun and highly elliptical orbit.
  • Exactly 365 days, the same as Earth, despite its further distance from the Sun.
  • Approximately 100 Earth years, with its orbit being faster due to its smaller size.
  • Over 503 Earth years, as it is the farthest known dwarf planet in the solar system.

• What is the composition of Pluto's surface?

  Pluto's surface is composed of a diverse mix of ices and rock. The ices include nitrogen, methane, and carbon monoxide, which can exist as gas, liquid, or solid on Pluto due to its extreme temperature variations. These ices form a thin atmosphere when Pluto is closest to the Sun, and then freeze onto the surface as it moves away. The surface also shows large regions of water ice. Notably, Pluto displays a range of surface features, including plains, mountains, valleys, and craters. The dwarf planet's iconic heart-shaped region, known as Tombaugh Regio, is a large basin filled with nitrogen and carbon monoxide ices.

  • Mostly a mix of nitrogen, methane, and carbon monoxide ices.
  • Primarily silicate rocks and metals, with little to no ice due to its distance from the Sun.
  • Mostly liquid oceans covered with a thick layer of gaseous hydrogen and helium.
  • Covered in thick dust and sand, similar to the surface of Mars, but colder.

• What mission famously flew by Pluto to take detailed photographs?

  The mission that famously flew by Pluto to take detailed photographs is NASA's New Horizons. Launched in January 2006, New Horizons conducted a close flyby of Pluto in July 2015, providing the first-ever close-up images and detailed observations of the dwarf planet and its moons. This historic flyby revealed a wealth of information about Pluto's geology, atmosphere, and moons, vastly increasing our understanding of this distant world. New Horizons continued its journey into the Kuiper Belt, exploring other distant objects in the region, including the Kuiper Belt object 486958 Arrokoth in 2019.

  • NASA's New Horizons, which provided the first detailed images of Pluto and its moons.
  • The Hubble Space Telescope, using its powerful cameras to take high-resolution images from Earth's orbit.
  • Pluto Pathfinder, a mission similar to the Mars Pathfinder, which landed on Pluto and sent back photographs.
  • The Voyager 2 spacecraft, which visited Pluto after its tour of the outer planets in the 1980s.

• What is the name of the region in the solar system where Pluto is located?

  Pluto is located in a region of the solar system known as the Kuiper Belt. The Kuiper Belt is an area beyond the orbit of Neptune, filled with a vast number of small, icy bodies that are remnants from the solar system's formation. This region is similar to the asteroid belt but is far larger, extending from about 30 astronomical units (AU) from the Sun out to about 50 AU. Pluto is one of the most well-known objects in this region and was considered the ninth planet in our solar system until 2006 when it was reclassified as a "dwarf planet."

  • The Asteroid Belt
  • The Oort Cloud
  • The Kuiper Belt
  • The Heliopause

• How many moons does Pluto have?

  Pluto has five known moons. The largest and most famous of these is Charon, discovered in 1978. Charon is nearly half the size of Pluto and shares a unique gravitational relationship with it, making the two bodies more of a binary system than a typical planet-moon pair. The other four moons are smaller and were discovered more recently: Nix and Hydra were both discovered in 2005, Kerberos was discovered in 2011, and Styx was discovered in 2012. These moons are much smaller than Charon and orbit Pluto at greater distances.

  • Two
  • Three
  • Five
  • Eight

• What is the size of Pluto compared to Earth?

  Pluto is significantly smaller than Earth. Its diameter is approximately 2,377 kilometers (1,477 miles), which is about 18.5% of Earth's diameter. To put it in perspective, Earth's diameter is about 12,742 kilometers (7,918 miles). This small size is one of the reasons Pluto was reclassified from a planet to a dwarf planet. In terms of volume, you could fit nearly 150 Plutos inside Earth. This size difference also means that Pluto's gravity is much weaker than Earth's, with surface gravity only about 1/15th that of Earth's.

  • About half the size of Earth
  • Comparable to Earth's moon in size
  • Comparable to Earth in size
  • About 1/6 of Earth's diameter

• What is the temperature range on Pluto?

  The temperature on Pluto is extremely cold, ranging from about -375 to -400 degrees Fahrenheit (-225 to -240 degrees Celsius). These frigid temperatures are due to Pluto's great distance from the Sun, averaging about 3.7 billion miles (5.9 billion kilometers). As a result, the Sun provides little warmth, leaving Pluto's surface covered in ice, including frozen nitrogen, methane, and carbon monoxide. The variation in temperature is relatively small because Pluto's thin atmosphere does little to retain heat.

  • -50 to -100 degrees Fahrenheit (-45 to -73 degrees Celsius)
  • -375 to -400 degrees Fahrenheit (-225 to -240 degrees Celsius)
  • 0 to -50 degrees Fahrenheit (-18 to -45 degrees Celsius)
  • 100 to 150 degrees Fahrenheit (38 to 66 degrees Celsius)

• What are the unique features of Pluto's atmosphere?

  Pluto's atmosphere is unique and complex, despite being thin. It is primarily composed of nitrogen, with traces of methane and carbon monoxide. One of the most remarkable features is that it extends much higher in altitude relative to the planet's size compared to Earth's atmosphere. The atmosphere is also subject to dramatic changes, expanding as Pluto moves closer to the Sun and its surface ices sublimate, and then collapsing as it moves away and the temperatures drop, causing the gases to freeze back onto the surface. Additionally, the atmosphere creates a blue haze, as seen in images sent back by the New Horizons spacecraft, caused by the scattering of sunlight by tiny particles.

  • Rich in oxygen and water vapor, similar to Earth
  • Composed mainly of hydrogen and helium, like a gas giant
  • Extremely dense and hot, with high levels of volcanic activity
  • Thin, primarily nitrogen, with seasonal changes and a blue haze

• What makes Pluto's orbit unique?

  Pluto's orbit is characterized by its interaction with Neptune, known as a vZLK (von Zeipel-Lidov-Kozai) oscillation, leading to both stability and instability. This resonant relationship prevents their orbits from colliding, despite Pluto's highly eccentric orbit with an eccentricity of 0.25, making it elongated. Additionally, the gravitational influences of other gas giants contribute to stabilizing Pluto's orbit. This complex dance highlights the dynamic interplay of forces governing the outer solar system.

  • Involves a special resonance with Neptune and contributions from other gas giants, creating a stable yet eccentric path.
  • Results in regular collisions with Neptune, affecting its classification as a planet.
  • Ensures a consistent temperature across its orbit, distinguishing it from other dwarf planets.
  • Restricts its visibility from Earth to specific times based on orbital position.

• How does Pluto's size compare to Earth's Moon?

  Pluto is smaller than Earth's Moon. The diameter of Pluto is about 2,377 kilometers (1,477 miles), whereas the diameter of Earth's Moon is about 3,474 kilometers (2,159 miles). This makes Pluto about two-thirds the size of the Moon. This comparison is often surprising, as many people assume that planets are larger than moons by default. However, Pluto's classification as a dwarf planet and its smaller size compared to the Moon are part of what makes it and other objects in the Kuiper Belt so interesting to astronomers and planetary scientists.

  • Smaller than Earth's Moon, about two-thirds the size of the Moon.
  • Roughly the same size as Earth's Moon, with only a slight difference in diameter.
  • Larger than Earth's Moon, but not by a significant amount.
  • Pluto is only about a quarter of the size of Earth's Moon, much smaller than most natural satellites in the solar system.

• How does Pluto's rotation period compare to its orbit period?

  Pluto's rotation period, the time it takes to complete one spin on its axis, is approximately 6.4 Earth days. This rotation period is synchronous with the orbit of its largest moon, Charon, meaning Pluto and Charon always show the same face to each other. This phenomenon is known as tidal locking. In comparison, Pluto's orbit period around the Sun, its year, is about 248 Earth years. This vast difference between the rotation period and the orbit period is typical for objects in the outer solar system, where orbital periods are significantly longer due to the vast distances from the Sun.

  • About 6.4 Earth days for rotation and 248 Earth years for its orbit around the Sun.
  • Pluto's rotation period is exactly 248 Earth years, the same as its orbit period, meaning it only rotates once every Pluto year.
  • Pluto's rotation period is about 24 hours, similar to Earth, and its orbit period is 248 Earth years.
  • Pluto has a rapid rotation period of only a few hours, contrasting with its long orbit period of 248 Earth years.

• What is the Charon-Pluto system, and why is it unique?

  The Charon-Pluto system is a unique pairing in our solar system where the moon, Charon, and the dwarf planet, Pluto, orbit each other in a synchronous manner. This system is unique because Charon is relatively large compared to Pluto, being about half its size. In most other planet-moon systems, the moon is significantly smaller than the planet it orbits. In the Charon-Pluto system, both bodies orbit a point in space between them, known as the barycenter, which is above Pluto's surface. This mutual orbit leads to both bodies showing the same face to each other at all times. The Charon-Pluto system is often referred to as a double dwarf planet or binary system due to these characteristics.

  • A system where Charon orbits Pluto very closely, causing extreme tidal effects
  • A binary asteroid system in the Kuiper Belt unrelated to Pluto
  • A binary system where Pluto and its moon Charon orbit each other
  • A region on Pluto named after the discoverer of Charon

• How were Pluto's additional moons discovered?

  Pluto's moons beyond Charon were identified through collaborative efforts involving various telescopes, with the Hubble Space Telescope playing a key role. Nix and Hydra were discovered in 2005, Kerberos in 2011, and Styx in 2012. These findings were pivotal for the New Horizons mission's exploration of Pluto and its moons.

  • During manned missions to Pluto in the early 2000s
  • Using multiple telescopes from the 2000s
  • Through observations from ground-based telescopes in the 1990s
  • Accidentally, during a Mars flyby mission

• What geological features have been identified on Pluto?

  Pluto's geological features, revealed by the New Horizons mission, are diverse and complex. Notable features include vast plains, such as Sputnik Planitia, a large ice plain made of nitrogen, carbon monoxide, and methane ices. Mountain ranges with peaks as high as 11,000 feet (3,500 meters), likely composed of water ice, have been identified. Pluto also has large regions of rugged terrain with ridges and troughs, suggesting geological activity. Additionally, there are signs of cryovolcanism, where icy material rather than molten rock is ejected, and possible dunes made from tiny particles. The presence of these features suggests that Pluto may be geologically active, a surprising discovery given its size and distance from the Sun.

  • Large liquid oceans and extensive forested regions
  • Vast plains of nitrogen ice, mountain ranges, and signs of cryovolcanism
  • Extensive sand dunes and large deserts similar to those on Mars
  • Massive impact craters covering the majority of the surface

• What are the theories about the formation of Pluto?

  The formation of Pluto is thought to be similar to that of other Kuiper Belt objects. According to prevailing theories, Pluto formed about 4.5 billion years ago from the accretion of ice and rock in the Kuiper Belt region. This process involved the gradual coalescence of dust and particles in the protoplanetary disk that orbited the early Sun. Over time, these materials accumulated to form the small, icy body we know as Pluto. Some theories suggest that Pluto's composition and its orbit may have been influenced by gravitational interactions with Neptune and other Kuiper Belt objects, which could explain some of its unique characteristics and its current position in the solar system.

  • As a result of a collision between Neptune and another large body in the early solar system
  • From the accretion of ice and rock in the Kuiper Belt region
  • Ejected from the asteroid belt due to Jupiter's gravitational forces
  • Formed from the remnants of a destroyed fifth gas giant planet

• How does the Kuiper Belt, where Pluto is located, differ from the Asteroid Belt?

  The Kuiper Belt and the Asteroid Belt are two distinct regions in our solar system with different compositions and locations. The Kuiper Belt is located beyond the orbit of Neptune, extending from about 30 to 55 astronomical units (AU) from the Sun. It contains a large number of icy bodies, including dwarf planets like Pluto. In contrast, the Asteroid Belt is located between Mars and Jupiter, ranging from about 2 to 3.2 AU from the Sun, and is primarily composed of rocky and metallic asteroids. The objects in the Kuiper Belt are generally larger and icier, reflecting their formation farther from the Sun in a colder environment. The Asteroid Belt's objects are more varied in composition, but tend to be smaller and less icy.

  • The Kuiper Belt is closer to the Sun and contains primarily metallic asteroids
  • The Kuiper Belt is farther from the Sun and has more icy bodies compared to the rocky Asteroid Belt
  • The Asteroid Belt contains more dwarf planets and comets than the Kuiper Belt
  • There is no significant difference; they are part of the same continuous belt of objects

• What role does Pluto play in studying the outer solar system?

  Pluto plays a crucial role in studying the outer solar system, particularly in understanding the Kuiper Belt, where it resides. As one of the largest and first-discovered objects in this region, Pluto serves as a key example of a Kuiper Belt Object (KBO). Studying Pluto helps astronomers understand the composition, formation, and evolution of other KBOs. Its unique orbit, geological features, and atmosphere provide insights into how objects in this distant region interact with solar radiation and the rest of the solar system. Pluto's exploration, especially through the New Horizons mission, has shed light on the diversity and complexity of objects in the outer solar system, challenging previous notions and expanding our knowledge of these distant worlds.

  • A key example of a Kuiper Belt Object, helping understand the composition, formation, and evolution of objects in this distant region.
  • Mainly serves as a comparison for comets entering the inner solar system from the Oort Cloud.
  • Acts as a gravitational balance for Neptune, preventing other objects from disturbing its orbit.
  • Its role is limited due to its small size and the fact that it's no longer classified as a planet.

• How do the surface features of Pluto provide clues about its geological history?

  Pluto's surface features offer significant clues about its geological history. The diverse landscape, including mountains, plains, valleys, and craters, indicates a complex and active geological past. The presence of mountains made of water ice suggests past tectonic activity. Plains like those in Sputnik Planitia, made of nitrogen and carbon monoxide ices, hint at glacial and possibly sub-surface geologic processes. The variation in crater distribution across the surface provides information about the age of different regions – fewer craters indicate younger surfaces, suggesting ongoing resurfacing processes. These features collectively suggest that Pluto has been geologically active, possibly driven by internal heating mechanisms, despite its small size and distance from the Sun.

  • Indicate a complex and active geological past, with tectonic activity, glacial processes, and ongoing resurfacing.
  • Show that Pluto has been geologically inactive, with surface features remaining unchanged for billions of years.
  • Suggest that Pluto's surface is entirely shaped by impacts from other Kuiper Belt objects, with no internal geology.
  • Indicate a history of extensive volcanic activity, with lava flows shaping most of Pluto's surface.

• What is the importance of the heart-shaped region on Pluto named Tombaugh Regio?

  The heart-shaped region on Pluto, named Tombaugh Regio, is significant for several reasons. Its distinct color and composition set it apart from the rest of Pluto's surface. The western lobe of Tombaugh Regio, known as Sputnik Planitia, is a large ice plain made primarily of nitrogen ice, with some methane and carbon monoxide, and is geologically young, indicating recent geological activity. This area also appears to be a significant reservoir of nitrogen, which is crucial for Pluto's thin atmosphere. The region's unique features, such as its alignment with Pluto's tidal axis, suggest interactions with internal processes. Studying Tombaugh Regio provides valuable insights into Pluto's geological and atmospheric evolution and raises intriguing questions about planetary processes in cold environments.

  • Shows recent geological activity, a significant reservoir of nitrogen, and provides valuable insights.
  • Believed to be the site of a massive impact, explaining Pluto's tilted orbit and other anomalies.
  • Contains evidence of past microbial life, making it a primary target for future astrobiological missions.
  • Acts as a giant solar reflector, impacting Pluto's temperature and possibly affecting its orbit.

NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute, Public domain

About Pluto

Pluto, once considered the ninth planet from the Sun in our Solar System, has a fascinating history and remains an object of great interest among astronomers and the public alike. Here's an overview of this distant world:

Discovery and Classification
- Discovery: Pluto was discovered by Clyde Tombaugh in 1930 at the Lowell Observatory in Arizona, filling what was believed to be a gap in the Solar System's architecture.
- Reclassification: In 2006, the International Astronomical Union (IAU) reclassified Pluto as a "dwarf planet" due to its size and the discovery of other similar-sized objects in the Kuiper Belt, a region of the Solar System beyond Neptune filled with icy bodies.

Physical Characteristics
- Size: Pluto is relatively small, with a diameter of about 2,377 kilometers, making it about one-sixth the width of Earth.
- Composition: It has a rocky core surrounded by a mantle of water ice, with a surface covered in nitrogen ice, methane, and carbon monoxide.
- Atmosphere: Pluto has a thin atmosphere composed mostly of nitrogen, with traces of methane and carbon monoxide. This atmosphere expands when Pluto is closer to the Sun and freezes when it moves away.

Moons
- Pluto has five known moons: Charon, Nix, Hydra, Kerberos, and Styx. Charon, the largest of these moons, is so big relative to Pluto that they are sometimes considered a binary system. The pair orbits a point in space between them due to their gravitational interaction.

Orbit and Rotation
- Pluto's orbit is highly eccentric, taking it on a long journey around the Sun that lasts 248 Earth years. Its orbital path is inclined relative to the ecliptic plane of the Solar System, and it occasionally crosses Neptune's orbit.
- A day on Pluto (a full rotation on its axis) lasts about 153 hours, or just over six Earth days.

Exploration
- New Horizons Mission: In July 2015, NASA's New Horizons spacecraft made a historic flyby of Pluto, providing the first close-up images and a wealth of scientific data about Pluto and its moons. The mission revealed towering mountains of ice, vast plains, and a surprisingly complex and active landscape.

Pluto's reclassification sparked debate and interest in what constitutes a planet and has led to increased study of the Kuiper Belt and its myriad of mysterious objects. Despite its dwarf planet status, Pluto remains an icon of exploration and curiosity, representing the ever-expanding frontier of our Solar System.