I think 2016 will be (and should be) remembered for two things: the putative discovery of the 9th planet in the solar system, and the announcement of the first observation of gravitational waves.
YouTube This video gives a brief introduction to the discovery of gravitational waves, although it omits one important point, which is that EM astronomy cannot directly observe anything older than the CMBR (the first 380 000 years after the Big Bang) whereas GW astronomy has the potential of making observations back to the first seconds.
(Also the peak power output of the black hole merger was 50 times the power output of the visible universe, not 10 times as stated in the video. The main uncertainty of this figure is due to the uncertainty of the power of the universe, not of the black hole merger.)
A sample of notable scientific events in 2016 include the discovery of the 49th known Mersenne prime , the first vertical powered landing of a suborbital rocket on a floating platform, the discovery of flowing water on present-day Mars, the first landing on a comet, and the first high quality scientific observations of Pluto.
In other astronomy news, the closest known star to the Sun had its name standardized to Proxima Centauri in August (previously Alpha Centauri C), and a planet in its habitable zone was discovered just 3 days later. It weighs 1.3 Earth masses. The star itself was discovered (and its current name proposed) in 1915.
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