The Chicxulub impactor (// CHEEK-shə-loob), also known as the K/Pg impactor and (more speculatively) as the Chicxulub asteroid, was an asteroid or comet at least 15 kilometres in diameter  which struck the Earth at the end of the Cretaceous, approximately 66 million years ago, creating the Chicxulub crater. It impacted a few miles from the present-day town of Chicxulub in Mexico, after which the impactor and its crater are named. Because the estimated date of the object's impact and the Cretaceous–Paleogene boundary (K–Pg boundary) coincide, there is a scientific consensus that its impact was the Cretaceous–Paleogene extinction event which caused the death of most of the planet's non-avian dinosaurs and many other species.
Astronomical origin theories
Before the 2016 studies into the origin of the impactor, there were several theories, which all conflicted with each other and with the 2016 findings. In September 2007, William F. Bottke, David Vokrouhlický, and David Nesvorný proposed an origin for the impactor in an article published in Nature. This argued that a collision in the asteroid belt 160 million years ago resulted in the Baptistina family of asteroids, the largest surviving member of which is 298 Baptistina. They proposed that the Chicxulub impactor was an asteroid member of this group, referring to the large amount of carbonaceous material present in microscopic fragments of the object, suggesting that it was a member of a rare class of asteroids called carbonaceous chondrites, like Baptistina. According to Bottke, the Chicxulub impactor was a fragment of a much larger parent body about 170 km (110 mi) across, with the other impacting body being around 60 km (40 mi) in diameter. However, in 2011 new data from the Wide-field Infrared Survey Explorer revised the date of the collision which created the Baptistina family to about 80 million years ago, casting doubt on the theory, as typically the process of resonance and collision of an asteroid takes many tens of millions of years.
2016 Impact crater study and findings
In the Spring of 2016, a coalition of scientists undertook core sampling from the peak ring of the Chicxulub crater, releasing their findings in the Spring of 2017. They concluded that a 15km-wide impactor initially dug a hole in Earth's crust 100km across and 30km deep, which then collapsed, leaving a crater just over 177km across and about 20km deep, establishing that the energy that went into making the crater when the asteroid struck was equivalent to 10 billion Hiroshima A-bombs. 
It was learned that the stratospheric aerosol injection caused by the impact at that particular location created a particularly toxic 'global winter' due to the heavy presence of sulfur at the impact site, resulting in atmospheric contamination of sulfuric acid on a global scale that caused a breakdown in the food chain, leading to the demise of nearly 75% of life on earth, including most non-avian dinosaurs. 
Notes and references
- Nicholas M. Short, Sr., Crater Morphology Some Characteristic Impact Structures at nasa.gov, accessed January 2013
- The article by Nicholas M. Short, Sr. appears to have moved, but the image above does not appear to have moved with it. See Crater Morphology Some Characteristic Impact Structures at fas.org, Accessed December 9, 2015.
- "Dinosaur extinction: Scientists estimate 'most accurate' date". BBC News. Retrieved 2015-10-28.
- "International Consensus — Link Between Asteroid Impact and Mass Extinction Is Rock Solid". www.lpi.usra.edu. Retrieved 2015-10-28.
- Schulte, Peter (March 5, 2010). "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary" (PDF). Science. 327: 1214–8. Bibcode:2010Sci...327.1214S. PMID 20203042. doi:10.1126/science.1177265. Archived from the original (PDF) on June 25, 2015. Retrieved 2015-06-25.
- Tammy Plotner, Did Asteroid Baptistina Kill the Dinosaurs? Think other WISE... in Universe Today (2011) at universetoday.com
- "Smashed asteroids may be related to dinosaur killer" Reuters, February 2, 2010