Ecosystem refers to a d

istinct system of interdependent plants and animals, along with their physical environment. An ecosystem may be as large as the entire Earth, or as small as a pond. Earth Observing System (EOS) refers to a series of small- to intermediate-sized spacecraft that :is the centerpiece of NASA's M:ission to Planet Earth. Planned for launch beginning in 1998, each of the EOS spacecraft will carry a suite of instruments designed to study global change.