Understanding Crescent Phases

Crescent phases occur when a planet is between the Sun and the observer. The illuminated portion of the planet we see is a thin sliver.

Mars's Perspective

From Mars, we need to consider the relative positions of the Sun, Mars, and the other planets in our solar system. Here's the breakdown:

* Inner Planets (Mercury and Venus): These planets orbit closer to the Sun than Mars. From Mars, they will *always* appear as crescent phases or fully illuminated. This is because they will either be between Mars and the Sun (crescent) or on the opposite side of the Sun from Mars (fully illuminated).

* Outer Planets (Jupiter, Saturn, Uranus, Neptune): These planets orbit further out than Mars. They will *never* appear as crescent phases from Mars. This is because they will always be farther from the Sun than Mars, and we'll never see them between the Sun and Mars.

The Answer

The planets that would *never* be visible as crescent phases from Mars are:

* Jupiter

* Saturn

* Uranus

* Neptune