Earth is the only planet in the Habitable Zone.

• A. True
• B. False
• C. Not specified
• D. Only Mars is in Habitable Zone

Answer: (A)

The habitable zone is the region around a star where a planet with an atmosphere like Earth’s could maintain liquid water on its surface. For the Sun, the inner edge is set by conditions that would cause oceans to boil if a planet were too close, and the outer edge by conditions where even a greenhouse effect wouldn’t keep water from freezing. In our solar system, Venus sits inside the inner edge (too hot for liquid water today) and Mars sits beyond the outer edge (too cold). That leaves Earth as the only planet currently within the Sun’s habitable zone. It’s worth noting that around other stars the boundaries shift with their brightness, so other exoplanets can be in their star’s habitable zone, but in our solar system Earth is the sole candidate with liquid water on the surface under present conditions.