Why has the number of known satellites for the inner planets remained almost constant while the number of known satellites for outer planets has increased during the past 400 years?

Answer 1

Two reasons basically. One, the inner planets are a lot closer and therefore accessible by even modest telescopes. We know that Mercury and Venus have no moons and Mars has two small ones. Beyond that optical telescopes on earth have a little trouble seeing something as small as a moon from that distance. Which brings us to reason two - spaceships.

The spacecraft we've sent to the systems of Jupiter and Saturn have discovered literally dozens of previously unknown moons. They were simply too small and too close to their primaries to show up on earth-bound telescopes. We've also gotten our first good looks at Saturn's rings and probably posed more questions than we answered.

Answer 2

The inner planets are closer to the Sun and are subject to stronger gravitational forces, making it harder for natural satellites to form and remain in stable orbits. The outer planets have more moons because they are farther from the Sun, allowing for more stable satellite formation due to weaker gravitational interactions and more abundant material in the outer solar system. Additionally, advancements in technology have made it easier to detect and observe smaller objects in the outer solar system, leading to the discovery of more moons around outer planets in recent centuries.