It is an interstellar object, travelling through our solar system, never to return, and was first observed from Hawaii in October 2017. It's called 'Oumuamua, meaning "guest" or "scout" in Polynesian, and is approximately 400 meters long, weighing 10 grams per m3. You can read more about it in Titan: "UiO-forskere kan ha påvist en hybelkanin i verdensrommet".
The full scientific article on the phenomenon can be read in The Astrophysical Journal Letters.