The video introduces Bernardinelli-Bernstein, a large Oort cloud comet also known as C/2014 UN271. Discovered in 2014 by astronomers Pedro Bernardinelli and Gary Bernstein using the Dark Energy Survey, this comet is the largest ever observed, measuring between 63 and 93 miles across. The video explains the Oort cloud, a spherical layer of icy objects surrounding the sun, and details the comet's orbit, including its perihelion and aphelion. Bernardinelli-Bernstein will approach the solar system in 2031 but will not be visible to the naked eye. The comet's composition is described as a cosmic snowball of rock dust and frozen gases.

When will the closest approach of the Bernardinelli-Bernstein comet to Earth occur?

What is the composition of a comet as described in the text?