Visitors from outer space (abbr.)

• Non-earthlings, for short
• They might come in saucers, for short
• Saucer's contents, for short
• UFO flyers
• Riders in 10-Across
• "MIB" characters
• UFO pilots, ostensibly
• "Independence Day" foes: Abbr
• UFO passengers, perhaps

Wikipedia Word definitions in Wikipedia
ETS is an abbreviation of: