This inert gas is atomic number 18; you should "naut" search any further
[DOC] [TLE] When Biospheres Collide - NASA History Homepage [PAR] to locate a source whose URL no longer works, you may contact the .... to be 
hoped that NASA's future activities in planetary protection will ..... searches for, 
and attempts to protect, extraterrestrial biospheres or ...... 18, http://www.hq.nasa.