Xenon was discovered in 1898 by William Ramsay and Morris Travers, the last of the stable noble gases they extracted from liquefied air, present only in the barest trace. Its name comes from the Greek xenos, stranger or foreigner. Xenon is a heavy, colourless, odourless gas, used in bright arc lamps and as a surprisingly effective general anaesthetic. Rare and costly, xenon lights bright arc and camera-flash lamps, drives the ion thrusters that propel some spacecraft, and serves in medical imaging, while its short-lived radioactive isotopes are watched for as telltale signs of nuclear reactions and explosions.
Xenon's anaesthetic property, discovered in the 1940s and confirmed clinically only decades later, makes it one of the safest general anaesthetics known, since it produces almost none of the cardiovascular side effects of conventional agents, though its high cost and scarcity have kept it a niche option used mainly in specialist and research settings rather than routine surgery. In fundamental physics, tanks of ultra-pure liquid xenon are now the leading medium for experiments such as XENON1T and LUX-ZEPLIN, which sit deep underground hoping to catch the faint recoil of a hypothetical dark-matter particle striking a xenon nucleus, placing this once merely rare gas at the frontier of the search for the universe's missing mass.