« Starlink—Elon Musk Discusses its Status, Plans, and Ambitions | Main | See Spot Dance »
Wednesday, June 30, 2021
CONTINUITY: Comet Bernardinelli-Bernstein
Comet Bernardinelli-Bernstein (C/2014 UN271) was first imaged in October 2014 by the Dark Energy Survey with a four metre telescope in Chile, but not identified as a comet until 2021-06-22 when a coma was first observed around the object at a distance of 20.18 astronomical units (the mean distance of the Earth from the Sun). Based upon its brightness and estimates of its albedo (reflectivity), this appears to be a huge object—between 100 and 200 kilometres in diameter. By comparison, the nucleus of Comet Hale-Bopp (C/1995 O1) was estimated to be 40 to 80 km in diameter. Comet Bernardinelli-Bernstein is comparable in size or larger than estimates of the Chicxulub impactor which caused a mass extinction on Earth around 66 million years ago.
This object will never get closer to the Sun than 10.95 astronomical units: around the distance of Saturn, and consequently will never develop a large tail or be visible from Earth with the unaided eye. But this discovery, which probably wouldn't have been made without the recently-developed and specialised (for an entirely different purpose) instruments of the Dark Energy Survey, highlights that the risk to Earth from comets, which can drop into the inner solar system from afar at any time, may be greater than that posed by the far more more numerous asteroids, whose orbits can be tracked and, if a threat is discovered, diverted long in advance. Suppose this comet were on course to impact the Earth. What could be done to prevent an extinction-level event? With our present technology, nothing.
Posted at June 30, 2021 12:23