CAMBRIDGE, Mass., Sept. 14 (UPI) -- Scientists say a search for the "building blocks" of the solar system has proved fruitful as they've added new objects to their cosmic inventories.
Icy rocks beyond the orbit of Neptune are known as trans-Neptunian objects. Pluto, now classified as a dwarf planet, is one of the largest. Halley's Comet is another. All are small and receive little sunlight, making them faint and difficult to spot, astronomers at the Harvard-Smithsonian Center for Astrophysics say.