Thursday 30 April 2015

Assessing the composition of ices on the surface of Makemake.

The Dwarf Planet Makemake is one of the three largest Trans-Neptunian Objects, with a diameter of about 1400 km, along with Pluto and Eris (2370 km 2330 km respectively). Makemake is thought to have a roughly circular orbit, remaining at about 45.7 AU from the Sun, while those of Pluto and Eris are more eccentric, taking them substantially closer to and further away from the Sun during the course of a single orbit (Pluto even spends part of its orbit inside the orbit of Neptune). All of these bodies are thought to have icy surfaces, and while those of Eris and Pluto are thought to undergo substantial heating and cooling as their distance from the Sun varies, leading to significant reworking of surface ices, that of Makemake if thought to remain close to 37K throughout its orbital cycle. This in theory means that the surface of Makemake should have undergone little reworking, and could therefore preserve a composition from early in the history of the Solar System.

The orbit of Makemake.  JPL Small Body Database Browser.

In a paper published in the journal Astronomy & Astrophysics on 10 April 2015 and on the arXiv database at Cornell University Library on 9 April 2015, Vania Lorenzi of the Fundación Galileo Galilei, Noemi Pinilla-Alonso of the Department of Earth and Planetary Sciences at the University of Tennessee and Javier Licandro of the Instituto Astrofísico de Canarias and the Departamento deAstrofísica at the Universidad de La Laguna, describe the results of a spectrographic analysis of the surface of Makemake carried out with the medium-resolution spectrograph ISIS on the 4.2 m William Herschel Telescope at the Roque de LosMuchachos Observatory on La Palma Island in the Canaries.

While all ices reflect light, specific ices will only do so at specific wavelengths, enabling astronomers to determine the surface composition of remote icy objects by analysing the spectra of sunlight reflected from them.

Lorenzi et al. were able to observe Makemake for 6.3 hours, 82% of one of its rotational periods (a ‘day’ on the surface of the Dwarf Planet), obtaining good data that enabled them to assess the composition of 70% of its surface. They found that the studied surface was homogenous (unvarying), which supports the idea that it is relatively unperturbed. The surface of Makemake appears to be covered by granular ice, containing a mixture of methane (CH4) and nitrogen (N2).

See also…

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