NASA's Hubble Space Telescope has recently identified a comet called "C/2014 UN271" as the largest comets ever discovered from the Oort cloud. The diameter of this gigantic nucleus is about 137 km (85 miles), which can cover the entire Hong Kong and some nearby cities. Its mass is estimated to be a hundred thousand times heavier than that of a typical comet found nearer to the Sun.

This comet has an extremely long orbital period and is believed to be originated from the Oort Cloud, a huge region thought to be located at the periphery of the Solar System. Through observation we know that this comet is travelling at 35,400 km per hour and it will reach its closest position to the Sun in 2031. However, it is still at about 1.6 billion km away from the Sun at its closest, which is around the orbit of Saturn. No worry as the Earth will not be hit by this comet.

The image shows the process of how the nucleus of comet was isolated from the image, and the comparison of comet nucleus sizes.

Credit: NASA photo/Man-To Hui, David Jewitt