The Surface Of Pluto-twin And Charon-like Objects

N. PINILLA-ALONSO, J. LICANDRO, Y R. GIL-HUTTON

Pasadena, Estados Unidos

Congreso; 38th Meeting of the AAS Division for Planetary Sciences; 2006

Division of Planetary Sciences, American Astronomical Society

In this presentation we report visible and near infrared spectra covering the 0.35-2.5 μm range of two big TNOs recently discovered, 2005 FY9 and 2003 EL61, and visible spectrum of 2003UB313 obtained with the 4.2 m William Herschel Telescope and the 3.58 m Telescopio Nazionale Galileo sited at El Roque de Los Muchachos Observatory (La Palma, Spain). In the case of 2005 FY9 and 2003UB313 the spectra of these large TNOs are similar to that of Pluto, with an infrared region dominated by very prominent absorption bands formed in solid CH4. The icy-CH4 bands in these new giants are significantly stronger than those of Pluto, implying that methane could be even more abundant on its surface. At wavelengths sorter than 0.6 microns, the spectra are almost featureless and red which most likely indicates the presence of complex organics on the surface as being hypothesized for Pluto and many other TNOs. The composition of the surface layers, in particular, the presence of N2 ice is discussed based in the central wavelength of methane-ice bands. In the case of 2003 El 61 we compare our spectrum with Charon's one and find that they have very similar characteristics, with a neutral featureless visible spectrum and strong water ice features at 1.5 and 2.2 μm. The presence of such deep water ice bands is not new among TNOs, it has been already refereed in the spectrum 1996 TO66, 2002 TX300 , and the brightest satellite of 2003 EL61. We complete our analysis of the surface of 2003 EL61 with a comparative study of these spectra.