Comet C/2017 K2 (PANSTARRS)

This Hubble Space Telescope image shows a fuzzy cloud of dust, called a coma, surrounding the comet C/2017 K2 PANSTARRS (K2), the farthest active comet ever observed entering the solar system. Hubble snapped images of K2 when the frozen visitor was over 2.4 billion kilometres from the Sun, just beyond Saturn's orbit. Even at that remote distance, sunlight is warming the frigid comet, producing a 128,000-kilometre-wide coma that envelops a tiny, solid nucleus. K2 has been traveling for millions of years from its home in the Oort Cloud, a spherical region at the edge of our solar system. This frigid area contains hundreds of billions of comets, the icy leftovers from the formation of the solar system 4.6 billion years ago. The image was taken in June 2017 by Hubble's Wide Field Camera 3.

Image Credit: NASA, ESA, and D. Jewitt (UCLA)
Explanation from: https://www.spacetelescope.org/images/opo1740a/