Comet 2I/Borisov is the most pristine visitor from outer space ever observed

Pristine, in astronomical terms, describes a comet that has never passed close enough to a star to be transformed by its searing heat.

from http://www.firstpost.com/tech/science/comet-2iborisov-is-the-most-pristine-visitor-from-outer-space-ever-observed-9482251.html