Hale-Bopp has a huge and extremely active nucleus. The nucleus is constantly erupting uupon itself, dust are spew out of the nucleus. The structure of the nucleus is more complex than astronomers had thought. There are traces of gases contained inside the ice. But the components remained in their own ice component while water ice remained seperate and uniform. Another thing is that the nucleus is tremendously huge. It was estimated to have a diameter of 19 to 25 miles long. Normally comets are to have a nucleus at about 3 miles long.