TY - JOUR
T1 - Red material on the large moons of Uranus
T2 - Dust from the irregular satellites?
AU - Cartwright, Richard J.
AU - Emery, Joshua P.
AU - Pinilla-Alonso, Noemi
AU - Lucas, Michael P.
AU - Rivkin, Andy S.
AU - Trilling, David E.
N1 - Funding Information:
This study was funded by a NASA Earth and Space Science Fellowship (grant number NNX14AP16H ), as well as NASA Solar System Observing grant 16-SSO016_2-0070 and Planetary Astronomy grant NNX10AB23G . Additional funding was provided by Tom Cronin and Helen Sestak whom we thank for their generous support. We also thank William Grundy for access to Uranian satellite SpeX spectra collected by his team between 2001 and 2006. Additionally, we thank the people of Hawaii for allowing us to use Mauna Kea for our observations, as well as the IRTF telescope operators and staff for providing observing support. We thank Daniel Tamayo for his input on dust dynamics in the Uranian system and for providing a helpful review of this manuscript. We also thank an anonymous reviewer for providing insightful comments as well.
Publisher Copyright:
© 2018
PY - 2018/11/1
Y1 - 2018/11/1
N2 - The large and tidally-locked “classical” moons of Uranus display longitudinal and planetocentric trends in their surface compositions. Spectrally red material has been detected primarily on the leading hemispheres of the outer moons, Titania and Oberon. Furthermore, detected H2O ice bands are stronger on the leading hemispheres of the classical satellites, and the leading/trailing asymmetry in H2O ice band strengths decreases with distance from Uranus. We hypothesize that the observed distribution of red material and trends in H2O ice band strengths results from infalling dust from Uranus’ irregular satellites. These dust particles migrate inward on slowly decaying orbits, eventually reaching the classical satellite zone, where they collide primarily with the outer moons. The latitudinal distribution of dust swept up by these moons should be fairly even across their southern and northern hemispheres. However, red material has only been detected over the southern hemispheres of these moons, during the Voyager 2 flyby of the Uranian system (subsolar latitude ∼81°S). Consequently, to test whether irregular satellite dust impacts drive the observed enhancement in reddening, we have gathered new ground-based data of the now observable northern hemispheres of these satellites (sub-observer latitudes ∼17–35°N). Our results and analyses indicate that longitudinal and planetocentric trends in reddening and H2O ice band strengths are broadly consistent across both southern and northern latitudes of these moons, thereby supporting our hypothesis. Utilizing a suite of numerical best fit models, we investigate the composition of the reddening agent, finding that both complex organics and amorphous pyroxene match the spectral slopes of our data. We also present spectra that span L/L’ bands (∼2.9–4.1 µm), a previously unexplored wavelength range in terms of spectroscopy for the Uranian satellites, and we compare the shape and albedo of the spectral continua in these L/L’ band data to other icy moons in the Jovian and Saturnian systems. Additionally, we discuss possible localized enhancement of reddening on Titania, subtle differences in H2O ice band strengths between the southern and northern hemispheres of the classical satellites, the distribution of constituents on Miranda, and the possible presence of NH3-hydrates on these moons. In closing, we explore potential directions for future observational and numerical modeling work in the Uranian system.
AB - The large and tidally-locked “classical” moons of Uranus display longitudinal and planetocentric trends in their surface compositions. Spectrally red material has been detected primarily on the leading hemispheres of the outer moons, Titania and Oberon. Furthermore, detected H2O ice bands are stronger on the leading hemispheres of the classical satellites, and the leading/trailing asymmetry in H2O ice band strengths decreases with distance from Uranus. We hypothesize that the observed distribution of red material and trends in H2O ice band strengths results from infalling dust from Uranus’ irregular satellites. These dust particles migrate inward on slowly decaying orbits, eventually reaching the classical satellite zone, where they collide primarily with the outer moons. The latitudinal distribution of dust swept up by these moons should be fairly even across their southern and northern hemispheres. However, red material has only been detected over the southern hemispheres of these moons, during the Voyager 2 flyby of the Uranian system (subsolar latitude ∼81°S). Consequently, to test whether irregular satellite dust impacts drive the observed enhancement in reddening, we have gathered new ground-based data of the now observable northern hemispheres of these satellites (sub-observer latitudes ∼17–35°N). Our results and analyses indicate that longitudinal and planetocentric trends in reddening and H2O ice band strengths are broadly consistent across both southern and northern latitudes of these moons, thereby supporting our hypothesis. Utilizing a suite of numerical best fit models, we investigate the composition of the reddening agent, finding that both complex organics and amorphous pyroxene match the spectral slopes of our data. We also present spectra that span L/L’ bands (∼2.9–4.1 µm), a previously unexplored wavelength range in terms of spectroscopy for the Uranian satellites, and we compare the shape and albedo of the spectral continua in these L/L’ band data to other icy moons in the Jovian and Saturnian systems. Additionally, we discuss possible localized enhancement of reddening on Titania, subtle differences in H2O ice band strengths between the southern and northern hemispheres of the classical satellites, the distribution of constituents on Miranda, and the possible presence of NH3-hydrates on these moons. In closing, we explore potential directions for future observational and numerical modeling work in the Uranian system.
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U2 - 10.1016/j.icarus.2018.06.004
DO - 10.1016/j.icarus.2018.06.004
M3 - Article
AN - SCOPUS:85048769945
SN - 0019-1035
VL - 314
SP - 210
EP - 231
JO - Icarus
JF - Icarus
ER -