Trans-Neptunian objects and Centaurs at thermal wavelengths. (arXiv:1905.07158v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Muller_T/0/1/0/all/0/1">Thomas M&#xfc;ller</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Lellouch_E/0/1/0/all/0/1">Emmanuel Lellouch</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Fornasier_S/0/1/0/all/0/1">Sonia Fornasier</a> (2) ((1) Max-Planck-Institut f&#xfc;r extraterrestrische Physik, Germany, (2) LESIA, Observatoire de Paris, Universit&#xe9; PSL, CNRS, Univ. Paris Diderot, Sorbonne Paris Cit&#xe9;, Sorbonne Universit&#xe9;, France)

The thermal emission of transneptunian objects (TNO) and Centaurs has been
observed at mid- and far-infrared wavelengths – with the biggest contributions
coming from the Spitzer and Herschel space observatories-, and the brightest
ones also at sub-millimeter and millimeter wavelengths. These measurements
allowed to determine the sizes and albedos for almost 180 objects, and
densities for about 25 multiple systems. The derived very low thermal inertias
show evidence for a decrease at large heliocentric distances and for
high-albedo objects, which indicates porous and low-conductivity surfaces. The
radio emissivity was found to be low ($epsilon_r$=0.70$pm$0.13) with possible
spectral variations in a few cases. The general increase of density with object
size points to different formation locations or times. The mean albedos
increase from about 5-6% (Centaurs, Scattered-Disk Objects) to 15% for the
Detached objects, with distinct cumulative albedo distributions for hot and
cold classicals. The color-albedo separation in our sample is evidence for a
compositional discontinuity in the young Solar System. The median albedo of the
sample (excluding dwarf planets and the Haumea family) is 0.08, the albedo of
Haumea family members is close to 0.5, best explained by the presence of water
ice. The existing thermal measurements remain a treasure trove at times where
the far-infrared regime is observationally not accessible.

The thermal emission of transneptunian objects (TNO) and Centaurs has been
observed at mid- and far-infrared wavelengths – with the biggest contributions
coming from the Spitzer and Herschel space observatories-, and the brightest
ones also at sub-millimeter and millimeter wavelengths. These measurements
allowed to determine the sizes and albedos for almost 180 objects, and
densities for about 25 multiple systems. The derived very low thermal inertias
show evidence for a decrease at large heliocentric distances and for
high-albedo objects, which indicates porous and low-conductivity surfaces. The
radio emissivity was found to be low ($epsilon_r$=0.70$pm$0.13) with possible
spectral variations in a few cases. The general increase of density with object
size points to different formation locations or times. The mean albedos
increase from about 5-6% (Centaurs, Scattered-Disk Objects) to 15% for the
Detached objects, with distinct cumulative albedo distributions for hot and
cold classicals. The color-albedo separation in our sample is evidence for a
compositional discontinuity in the young Solar System. The median albedo of the
sample (excluding dwarf planets and the Haumea family) is 0.08, the albedo of
Haumea family members is close to 0.5, best explained by the presence of water
ice. The existing thermal measurements remain a treasure trove at times where
the far-infrared regime is observationally not accessible.

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