Final answer:
Mars has a diameter most similar in size to that of planet Kepler 62c when compared to the diameters of Earth, Jupiter, and Saturn.
Step-by-step explanation:
The planet in our solar system that has an equator or diameter most similar in size to the equator or diameter of planet Kepler 62c is Mars. Considering the provided information, the smallest planet in the Kepler-62 system is about the size of Mars. Earth's diameter is about 13,000 kilometers as mentioned, and we know that Mars' diameter is roughly half that of Earth, positioning it nearly 6,500 kilometers in diameter.
Meanwhile, Jupiter's diameter is significantly larger, about 10 times that of Earth's, hence it would not match the size of Kepler 62c. Therefore, when comparing the diameters of Earth, Jupiter, Saturn, and Mars to Kepler 62c, Mars is the planet with a diameter closest to that of Earth, making it the best fit for the question at hand.