Which is Larger? Pluto or Eris?

Six years ago this month, Michael E. Brown, a professor of planetary astronomy at the California Institute of Technology, spotted an object in the night sky that was so bright and so far away that he was sure it was bigger than Pluto.

"Guaranteed," Dr. Brown said when he announced the discovery, half a year later, in July 2005.

Well...maybe not, after all.

In November, that object, now known as the dwarf planet Eris, passed in front of a dim, distant star. Astronomers led by Bruno Sicardy of the Paris Observatory measured how long the star disappeared behind Eris and, from that, calculated the width of Eris.

"It's clearly smaller," said Alain Maury, who observed the brief disappearance, or occultation, of the star at the San Pedro de Atacama Celestial Explorations Observatory in Chile.

For now, Drs. Maury and Sicardy decline to say exactly how small Eris is, because they first want to publish the results in the journal Nature. But they say that even accounting for the uncertainties in the observations, the largest possible Eris is smaller than the smallest possible Pluto.…

See NYT > Space & Cosmos for links to further info.