After 20 years and many moons, the Cassini spacecraft was sent crashing into Saturn.
"Enceladus has almost all of the ingredients you would need to support life as we know it on Earth," a NASA scientist said.
The year 2015 saw more than its fair share of extreme hydrologic events, both ruinous floods and severe drought. In the United States, attention remained focused on California, which is suffering the worst four-year drought on record.
The Cassini spacecraft has snapped another unforgettable portrait.
The concept of a Dyson Sphere is not a new one. It was first described by futurist writer Olaf Stapledon in his 1937 science fiction novel, Star Maker.
(Story continues below images.) Dramatic plumes on Saturn’s moon Enceladus, as seen by the Cassini probe during its flyby