The 50-cm Caisey Harlingten telescope at San Pedro de Atacama, Chile, where one of the successful observations took place. (credit: Photograph by A. Maury)
Eris, the largest dwarf planet in our solar system, made headlines in 2006 when scientists reported that it was larger and heavier than Pluto. New measurements are suggesting that Eris may actually be more like Pluto’s twin. The newly measured radius of Eris puts it within the error range of the accepted size of Pluto.
The dwarf planet Eris was discovered in 2005. Based on imaging, it was thought to have a radius of anywhere from 1,100 to 1,700 km, making it likely to be larger than Pluto (thought to have a radius between 1,150 and 1,200 km). Based on the orbit of its moon, Dysnoima, Eris's mass has been estimated to be about 27 percent larger than Pluto's.
Scientists were able to get a better handle on the size of Eris by observing it as it passed in front of a background star, a technique called stellar occultation. By observing how long Eris obscures the star (given how fast it is moving), you can determine the width of Eris at that point. By simultaneously measuring the occultation from different locations on Earth, astronomers were able to measure the width of Eris from different angles, and thus able to determine its shape.