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Chapter 12: Problem 26

Describe ways in which Pluto differs significantly from the classical Solar System planets.

Short Answer

Expert verified
Pluto has an elliptical and tilted orbit, is much smaller and less massive, composed of ice and rock, reclassified as a 'dwarf planet,' and has a binary system with its moon Charon.

Step by step solution

01

- Orbit Characteristics

Pluto's orbit is highly elliptical and inclined compared to the nearly circular and coplanar orbits of the classical planets. Specifically, Pluto's orbit is tilted by 17 degrees to the plane of the Solar System.
02

- Size and Mass

Pluto is much smaller and less massive than any of the classical planets. It has a diameter of about 2,377 kilometers and a mass that is only about 0.2% that of Earth.
03

- Composition

Pluto is composed primarily of ice and rock, unlike the terrestrial planets (which are rocky) and the gas giants (which are composed mostly of hydrogen and helium).
04

- Classification

In 2006, the International Astronomical Union (IAU) reclassified Pluto as a 'dwarf planet.' This distinguishes it from the eight classical planets.
05

- Satellites

Pluto has five known moons, the largest of which is Charon. This satellite is so large relative to Pluto that they form a binary system, which is unique among the classical planets.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Orbit Characteristics
Pluto's orbit is quite different from those of the classical planets. Most planets in our Solar System have orbits that are almost circular and align within the same flat plane, called the ecliptic plane. However, Pluto bucks this trend:
  • Elliptical Shape: Pluto's orbit is highly elliptical, meaning it is stretched out more than it is circular.
  • Inclination: Its orbit is also tilted about 17 degrees to the plane of the Solar System, making it much more angled compared to the orbits of other planets.
  • Distance from the Sun: Because of these characteristics, Pluto takes a very lengthy 248 Earth years to complete one orbit around the Sun.
These aspects make Pluto’s path through our Solar System unlike any of the classical planets.
Size and Mass
When comparing Pluto to the classical planets, its size and mass stand out as being remarkably tiny.
  • Diameter: Pluto has a diameter of about 2,377 kilometers, which makes it smaller than the Earth's Moon.
  • Mass: Its mass is only about 0.2% of Earth's mass. This is tiny compared to any of the classical planets, including Mercury, which is still much larger and heavier.
Because of its small size, Pluto has less gravity compared to planets like Earth and Jupiter, influencing its ability to retain an atmosphere.
Composition
Pluto's composition sets it apart from both terrestrial and gas giant planets.
  • Ice and Rock: Pluto is made up predominantly of ice and rock.
  • Surface Composition: Its surface is covered with a mixture of frozen nitrogen, methane, and carbon monoxide ices, unlike the rocky surfaces of terrestrial planets like Earth or Mars, and the gaseous surfaces of planets like Jupiter and Saturn.
This unique combination of materials and its cold environment distinguish Pluto from the more homogeneous compositions of classical planets in our Solar System.
Planet Classification
In 2006, the International Astronomical Union (IAU) reclassified Pluto as a 'dwarf planet.' This new classification differentiates it from the eight classical planets.
  • Criteria: A dwarf planet, according to the IAU, is an object that orbits the Sun, has enough mass for its gravity to shape it into a round form, but has not cleared its orbit of other debris.
  • Pluto's Status: Pluto fits this definition because it shares its orbit with other objects in the Kuiper Belt, a region beyond Neptune filled with small icy bodies.
This reclassification helps to underscore the differences in Pluto’s characteristics when compared to classical planets.
Moons and Satellites
One fascinating aspect of Pluto is its moons. Pluto has five known moons: Charon, Styx, Nix, Kerberos, and Hydra.
  • Charon: The largest moon, Charon, is so big compared to Pluto itself that they are often considered a binary system. Charon's diameter is about half that of Pluto's, making it unusually large for a moon relative to its parent planet.
  • Orbital Relationship: Pluto and Charon are tidally locked, which means they always show the same face to each other as they orbit a common center of mass that resides above Pluto's surface.
This unique relationship is unlike anything seen among the classical planets and their moons, adding another layer of intrigue to Pluto's profile.

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Most popular questions from this chapter

Some near-Earth objects are in binary systems, so it is possible to estimate their mass. How much energy would be released if a near-Earth asteroid with mass \(m=4.6 \times 10^{11} \mathrm{kg}\) hit Earth at a speed ( \(v\) ) of \(5 \mathrm{km} / \mathrm{s}\).

Earth's Moon has a diameter of \(3,474 \mathrm{km}\) and orbits at an average distance of \(384,400 \mathrm{km}\). At this distance it subtends an angle just slightly larger than half a degree in Earth's sky. Pluto's moon Charon has a diameter of \(1,186 \mathrm{km}\) and orbits at a distance of \(19,600 \mathrm{km}\) from the dwarf planet. a. Compare the appearance of Charon in Pluto's skies with the Moon in Earth's skies. b. Describe where in the sky Charon would appear as seen from various locations on Pluto.

Comet Halley has a mass of approximately \(2.2 \times 10^{14}\) kg. It loses about \(3 \times 10^{11} \mathrm{kg}\) each time it passes the Sun. a. The first confirmed observation of the comet was made in 230 BCE. Assuming a constant period of 76.4 years, how many times has it reappeared since that early sighting? b. How much mass has the comet lost since 230 BCE? c. What percentage of the comet's total mass does this amount represent?

How could you and a friend, armed only with your cell phones and a knowledge of the night sky, prove conclusively that meteors are an atmospheric phenomenon?

Kuiper Belt objects (KBOs) are actually comet nuclei. Why do they not display comae and tails? a. Most of the material has already been stripped from the objects. b. They are too far from the Sun. c. They are too close to the Sun. d. The comae and tails are pointing away from Earth, behind the object.
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