The extraordinary breadth of the Department reflects the interdisciplinary approaches required to understand complex systems like the Earth and the planets. Our faculty tackle a wide range of problems, from the Sun to the most distant planets, and from the center of the Earth to the tenuous ionized gases of the solar wind. We probe the interior of the Earth using seismic data, laboratory measurements, and computer modeling. We study both the ancient tectonics of the Earth and its ongoing activity. We explore Earth's upper atmosphere using spacecraft to measure magnetic fields and plasmas. Moving outward from Earth, we study other planets, their interiors, surfaces, atmospheres, and particle and field environments. No object in the solar system-not asteroids nor ions in the solar wind-are small enough to escape our attention. A central theme of the Department's researchers is to understand the origin and evolution of the solar system, the planets, Earth itself, and life on Earth."