Dwarf Planet Larger than Pluto
Eris Discovered to be Most Massive Kuiper Belt Object Known
Eris is confirmed to be the largest known solar system object beyond Neptune, forcing Pluto to retain its Dwarf Planet status.
Astronomer Mike Brown from CalTech has put the nail in the coffin for Pluto's planetary dreams. New data results from Hubble Space Telescope and Keck Observatory shows that dwarf planet Eris is larger than Pluto. "This was Pluto's last chance to be the biggest thing found so far in the Kuiper belt," Brown says.
Brown and graduate student Emily Schaller discovered that Eris is 27 percent more massive than Pluto. Measuring the amount of time it took Eris's moon Dysnomia to complete an orbit allowed them to estimate Eris's weight at 16.6 billion trillion kilograms. The density of Eris is about two grams per cubic centimeter, indicating that the dwarf planet is made of ice and rock, as is Pluto.
Eris is not only more massive than Pluto, its diameter is larger too. Eris is estimated to be 2400 km in diameter, and Pluto's diamter is 2320 km.
Eris has a highly ellipitical orbit like Pluto, only even more extreme. Pluto's orbit ranges from 30 AU to 50 AU, briefly coming inside Neptune's orbit, while Eris's orbit ranges from 38 AU to 97 AU. Eris's year is equal to 560 Earth years, and Pluto's year is equal to 250 Earth years. While Pluto was recently at its closest point to the sun in its orbit and is now heading back out, Eris is currently at about its farthest point in its orbit.
Eris and Pluto are both cold, but Eris, being farther out, is colder at well below 400 degrees Fahrenheit. Pluto's temperature is about -370 degrees Fahrenheit.
Pluto is believed to be a reddish-yellow color. As the New Horizons spacecraft reaches Pluto we will have better views and confirmation of its hue. Both dwarf planets are believed to have a frozen methane surface. Chemical changes due to solar radiation is what is responsible for their color changes, with Eris believed to be yellower due to its farther distance from the Sun.
Eris and its moon Dysnomia, which is about 150 kilometers in diameter, were discovered in 2005 with Palomar Observatory's 48-inch Samuel Oschin Telescope. Eris was briefly called Xena before its official name was bestowed on it. The dwarf planet-moon system were probably formed along with our solar system 4.5 billion years ago after a massive collision.
In order of size from largest to smallest, these are the solar system objects now known beyond Neptune: Eris (formerly Xena), Pluto, 2005 FY9, 2003 EL61, Sedna, and Quaoar. Does a dwarf planet larger than Eris lie yet undiscovered in the icy Kuiper belt? Only time will tell.
