Arecibo radar images of comet 46P/Wirtanen, taken during its close approach to Earth on December 16t

Arecibo radar images of comet 46P/Wirtanen, taken during its close approach to Earth on December 16th 2018. The comet nucleus seen here is about 1.4km in diameter. It’s rare for a comet to pass close enough to the earth that radar imaging is possible, and this is just the 8th time it’s been done.