View Full Version : Pluto or Eris: Which is Bigger?

2011-Oct-14, 10:00 PM
The controversy between Pluto and Eris regarding their status as “largest dwarf planet” continues. During a joint meeting of the American Astronomical Society Division for Planetary Sciences and the European Planetary Science Congress last week in Nantes, France, new data was presented that may help settle the debate. The new findings regarding this size of [...]

More... (http://www.universetoday.com/89901/pluto-or-eris-which-is-bigger/)

2011-Oct-28, 06:57 PM
Article in yesterday's LA Times about it (http://www.latimes.com/news/science/la-sci-eris-20111027,0,6101561.story)

Scientists' picture of Eris had remained fuzzy because its distance from Earth is so vast: It is about three times farther out from the sun than Pluto. Some estimates pegged Eris as about 25% larger than Pluto, but it was too far away to tell for sure.

"It's very difficult, because it's so small in the sky," said lead author Bruno Sicardy, a planetary scientist at Pierre and Marie Curie University and Observatory in Paris.

With such small, far-off objects, astronomers wait for what's known as a stellar occultation, in which the object will cross over a star, essentially casting a shadow over the Earth. The amount of starlight blocked by the object allows scientists to calculate the object's size.

Witnessing this stellar occultation last year required being in the right place at exactly the right moment during the brief time window that Eris was scheduled to block the star.

To spot the star-crossing, Sicardy's team asked telescope operators at 26 different sites around the world to make observations. Just three telescopes at two of those sites, both in Chile, managed to catch the event.

From the data, the researchers were able to calculate that the dwarf planet's diameter is about 1,445 miles — on a par with Pluto, which is somewhere between 1,429 and 1,491 miles across.

The fact that Eris is smaller than previously estimated means that the amount of light scientists had detected coming from it originated from a smaller-than-anticipated surface area — and therefore its surface is brighter than anyone had thought.

In fact, the new calculations make Eris one of the brightest objects in the solar system, even though its surface should have been darkened from bombardment by cosmic rays and micrometeorites.