Odd One Out — Mars, Saturn, and Mercury are planets; the Sun is a star. Identify the odd celestial body and explain.

Introduction / Context:
Astronomical classification distinguishes between planets (non-luminous bodies orbiting a star) and stars (self-luminous plasma spheres). Three options are planets; one is a star.

Given Data / Assumptions:

• Mars, Saturn, Mercury: planets of our Solar System.
• Sun: G-type main-sequence star, the central star of our Solar System.

Concept / Approach:
Identify whether each body is self-luminous via fusion (star) or reflects light (planet).

Step-by-Step Solution:
Mars → planet.Saturn → planet.Mercury → planet.Sun → star → outlier.

Verification / Alternative check:
Orbital role: planets orbit the Sun; the Sun does not orbit a Solar System star—it is the star being orbited.

Why Other Options Are Wrong:

• Mars, Saturn, Mercury: all non-luminous planets.

Common Pitfalls:
Confusing brightness with “planet vs star”; visible brightness depends on distance and size, but luminous mechanism is decisive.

Final Answer:
Sun