7. Pluto has been reclassified as a “dwarf planet” rather than a “planet” because
a. its orbit around the sun is not circular
b. it is smaller than the Earth
c. it is incapable of supporting life
d. none of the above

Pluto was reclassified as a dwarf planet in 2006 by the International Astronomical Union (IAU) because it fails to meet the third criterion for planet status: clearing its orbital neighborhood of other objects.​

Option Analysis

a. Its orbit around the sun is not circular
Pluto’s orbit is highly elliptical, but this trait is shared by other planets like Mercury and comets; orbital shape alone does not determine planetary status under IAU definitions.​

b. It is smaller than the Earth
Size varies among planets—Mercury and Mars are smaller than Earth—yet all qualify as planets; Pluto’s diameter of about 2,377 km is irrelevant to the classification criteria.​

c. It is incapable of supporting life
No planets in our solar system definitively support life, and the IAU definition excludes habitability as a factor; this remains speculative for all worlds.​

d. None of the above
Correct—Pluto orbits the Sun, is spherical due to hydrostatic equilibrium, but resides in the Kuiper Belt without dominating its path, unlike the eight planets.​

Pluto’s reclassification from planet to dwarf planet sparked global debate, but the IAU’s 2006 decision clarified solar system boundaries. This change stemmed from discoveries in the Kuiper Belt revealing Pluto as one of many similar icy bodies.​

IAU Planet Definition Breakdown

The IAU set three rules: orbit the Sun, achieve hydrostatic equilibrium (spherical shape), and clear the orbital neighborhood.​
Pluto meets the first two but fails the third—its mass is only 0.07 times that of nearby objects, unlike Earth’s dominance.​
Other dwarf planets like Eris share this trait, forming a distinct category.​

Common Misconceptions Debunked

• Elliptical orbits? Normal for many bodies, not disqualifying.​

• Small size? Mercury proves otherwise.​

• No life? Irrelevant to criteria.​

This reclassification maintains scientific consistency amid thousands of trans-Neptunian objects.​