Through a process of elimination, they were able to compare their lab results with the spectra of light reflected from Eris' surface using spectroscopic observations from the Multiple Mirror Telescope Observatory, Arizona. The team also gathered observations of Pluto's spectra from Kitt Peak National Observatory. Eris' surface ice composition could then be deduced and compared with that of Pluto.
"By combining the astronomical data and laboratory data, we found about 90 percent of Eris' icy surface is made up of nitrogen ice and about 10 percent is made up of methane ice, which is not all that different from Pluto," said co-author David Cornelison of Missouri State University.
Caltech's Mike Brown, who's Palomar Observatory team discovered Eris in 2005, attended Tegler's presentation on Tuesday and is confident about these new findings.
"My suspicion - not having read the paper yet - is that the answer is right, but only because it is the answer that we have always expected!" Brown told Discovery News.