Pluto's rival is tiny but shiny

摘要

POOR Pluto. It got kicked out of the planet club in 2006 after an even larger world, Eris, was found in the outer solar system. Now it seems Eris is no larger than Pluto -it simply looks bigger because its surface is blindingly bright. Observations by the Hubble Space Telescope in 2005 suggested Eris is at least 2400 kilometres wide, a few per cent wider than Pluto, which spans 2338 km. But the data left room for doubt. Last November, astronomers got their best chance yet to pin down Eris's size when it passed directly in front of a distant star and cast a small shadow on Earth.