They orbit between our planet and our star. Mercury and Venus make up half of our terrestrial planets, but we still know very little about them. As we take a closer look at our companions, we find more questions than answers.

From the beginnings of our solar system 4.5 billions years ago, there remain many clues to reveal its evolution. Remnant debris, asteroids, and comets are what's left of the building blocks to our celestial neighborhood.