Exospheric

Part of speech: adjective

Definitions

1. Pertaining to the outermost zone of a planetary atmosphere, this term indicates the region characterized by a sparse distribution of particles and minimal density
2. This descriptor refers to the highest layer in an atmosphere, denoting an area where the density of gas particles is exceedingly low and extends into outer space
3. Relating to the outermost layer of an atmospheric structure, this term signifies a region where particle density is extremely low and merges with the vacuum of outer space

Etymology: "Exospheric" is simply "exosphere" with the adjective-forming ending "-ic" added. The "exo-" part comes from Greek "exō," meaning "outside," and "sphere" comes from Greek "sphaira," a ball or globe. An exosphere is thus the outer shell of a planet's atmosphere, the layer where gas particles are so thin they can drift off into space. The ending "-ic" has a long road into English. It descends from the Latin suffix "-icus," which Latin itself inherited from earlier Italic forms, reaching back to a very old ending that marked a connection to a noun. It passed into English through Old French "-ique," and Middle English adopted it as "-ik," which later settled into the modern "-ic" spelling. That is why hundreds of English adjectives, from "atomic" to "tropic," end the same way.