If you want to visit (and not live in) the United States you must first obtain a visitor visa. Travelers from certain countries may be exempt. If you want to travel to the United States for reasons other than business or pleasure, such as study or work, you must apply for a visa in the appropriate category. DHS provides a full range of online resources to help you plan your trip, manage your arrival and if needed extend your stay.
Some astronomers called Eris our Solar System's tenth planet when it was first discovered. After a lot of discussion, astronomers decided to make up a new category for objects like Eris. That is where the idea of dwarf planets came from.
If you mean the dwarf planet 136199 Eris then I can answer to the question. Eris has a rocky core and icy mantle like other large trans-Neptunian objects like 20000 Varuna, 28978 Ixion, 38628 Huya, 50000 Quaoar, 90377 Sedna, 90482 Orcus, 134340 Pluto, 136108 Haumea, 136472 Makemake and 225088 (2007 OR10) for example.