Question

Assume that three irregularly shaped planetlike objects, each smaller than our Moon, have just been discovered orbiting the Sun at a distance of $35\mathrm{AU}$. One of your friends argues that the objects should be classified as planets because they are large and orbit the Sum. Another friend argues that the objects should be classified as dwarf planets, such as Pluto. State whether you agree or disagree with either or both of your friends. Explain your reasoning.

Short answer

Disagree with both; they are not planets or dwarf planets since they are not spherical.

Step-by-step solution

Define the Criteria for Planets

The International Astronomical Union (IAU) criteria for an object to be considered a planet are: (1) it must orbit the Sun, (2) it must be spherical due to its own gravity, and (3) it must have cleared its orbit of other debris. These criteria are crucial to distinguish planets from other Solar System bodies.

Define the Criteria for Dwarf Planets

According to the IAU, a dwarf planet must meet the following criteria: (1) it orbits the Sun, (2) it is spherical due to its own gravity, and (3) it has not cleared its orbital path of other debris. Additionally, it should not be a satellite of another body.

Analyze the Objects' Description

The problem describes the objects as 'irregularly shaped,' which suggests they do not meet the criteria for being spherical. This indicates that they cannot be classified as planets or dwarf planets as per IAU definitions.

Determine Agreement with Friends

Based on the analysis, the first friend's argument that these objects should be classified as planets is incorrect because they do not have a spherical shape and possibly have not cleared their orbits. The second friend's statement that they could be dwarf planets is also incorrect for the same reason: they lack a spherical shape, which is a requirement for being classified as a dwarf planet.

Key concepts

International Astronomical Union (IAU)

The International Astronomical Union, often abbreviated as IAU, is the global authority responsible for naming celestial bodies and defining astronomical standards and criteria. This organization plays a critical role in astronomy by establishing formal definitions for celestial objects, among other tasks.
The IAU is particularly significant when it comes to the classification of planets, dwarf planets, and other solar system bodies. In 2006, the IAU created the criteria we use today to differentiate between planets and dwarf planets, which was a significant step for the field of astronomy.

• These criteria help ensure uniformity and precision in how we understand and categorize the vast entities in our universe.
• The IAU's decisions often shape astronomers' and educators' understanding worldwide, affecting how textbooks are written and how scientific discussions are conducted.

Edit descriptions if needed, and be sure to maintain precision in scientific communication.

dwarf planets

Dwarf planets are an intriguing classification of celestial bodies within our Solar System. To be considered a dwarf planet, an object must meet several specific criteria set by the IAU:
• The object must orbit the Sun
• It should be approximately spherical in shape due to its own gravity
• Unlike planets, it does not need to have cleared its orbit of other debris
• It is not a satellite of another body
These criteria distinguish dwarf planets from planets by acknowledging that they can be part of a crowded orbital zone.

• Pluto is the most famous example of a dwarf planet, having been reclassified from planet status following the establishment of these criteria.
• Other examples include Eris, Haumea, Makemake, and Ceres.

Dwarf planets play an essential role in helping astronomers understand the diversity and complexity of our Solar System's formation.

orbital dynamics

Orbital dynamics is the study of the movements of celestial bodies as they interact with each other's gravitational forces. This field is crucial for understanding how things like planets, moons, and even artificial satellites travel through space.
The dynamics are governed by the laws of physics, primarily Newton's laws of motion and the law of universal gravitation. These principles determine the paths objects take, known as orbits.

• An object's orbit is influenced by its mass, the mass of nearby objects, and the initial conditions of its movement.
• A truly fascinating part of orbital dynamics is how objects can influence each other's orbits, often leading to complex and beautiful patterns.

Understanding these dynamics is essential for classifying planets and dwarf planets, as they relate to the criteria of orbit-clearing and the shapes objects assume.

celestial bodies

Celestial bodies refer to all types of natural objects visible in the sky, outside Earth's atmosphere. These include stars, planets, moons, asteroids, and comets, among others.
Each of these bodies has distinct characteristics that intrigue astronomers, helping them learn about the history and nature of the universe.

• Planets are celestial bodies that orbit a star and have cleared their orbital path.
• Stars, unlike planets, are huge spheres of gas that produce light and heat through nuclear fusion.
• Moons are natural satellites that orbit planets.

The discovery and classification of celestial bodies include the work of various scientific disciplines, involving observation and the implementation of criteria such as those created by the IAU. This assists in the structured categorization of these bodies, enabling a clearer understanding of space.