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Register a new userOn the surface composition of Tritons southern latitudes
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We present the results of an investigation to determine the longitudinal (zonal) distributions and temporal evolution of ices on the surface of Triton. Between 2002 and 2014, we obtained 63 nights of near-infrared (0.67-2.55 $mu$m) spectra using the SpeX instrument at NASAs Infrared Telescope Facility (IRTF). Triton has spectral features in this wavelength region from N$_2$, CO, CH$_4$, CO$_2$, and H$_2$O. Absorption features of ethane (C$_2$H$_6$) and $^{13}$CO are coincident at 2.405 $mu$m, a feature that we detect in our spectra. We calculated the integrated band area (or fractional band depth in the case of H$_2$O) in each nightly average spectrum, constructed longitudinal distributions, and quantified temporal evolution for each of the chosen absorption bands. The volatile ices (N$_2$, CO, CH$_4$) show significant variability over one Triton rotation and have well-constrained longitudes of peak absorption. The non-volatile ices (CO$_2$, H$_2$O) show poorly-constrained peak longitudes and little variability. The longitudinal distribution of the 2.405 $mu$m band shows little variability over one Triton rotation and is 97$pm$44$^{circ}$ and 92$pm$44$^{circ}$ out of phase with the 1.58 $mu$m and 2.35 $mu$m CO bands, respectively. This evidence indicates that the 2.405 $mu$m band is due to absorption from non-volatile ethane. CH$_4$ absorption increased over the period of the observations while absorption from all other ices showed no statistically signifcant change. We conclude from these results that the southern latitudes of Triton are currently dominated by non-volatile ices and as the sub-solar latitude migrates northwards, a larger quantity of volatile ice is coming into view.
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Triton possesses a thin atmosphere, primarily composed of nitrogen, sustained by the sublimation of surface ices. The goal is to determine the composition of Tritons atmosphere and to constrain the nature of surface-atmosphere interactions. We perform high-resolution spectroscopic observations in the 2.32-2.37 $mu$m range, using CRIRES at the VLT. From this first spectroscopic detection of Tritons atmosphere in the infrared, we report (i) the first observation of gaseous methane since its discovery in the ultraviolet by Voyager in 1989 and (ii) the first ever detection of gaseous CO in the satellite. The CO atmospheric abundance is remarkably similar to its surface abundance, and appears to be controlled by a thin, CO-enriched, surface veneer resulting from seasonal transport and/or atmospheric escape. The CH$_4$ partial pressure is several times larger than inferred from Voyager. This confirms that Tritons atmosphere is seasonally variable and is best interpreted by the warming of CH$_4$-rich icy grains as Triton passed southern summer solstice in 2000. The presence of CO in Tritons atmosphere also affects its temperature, photochemistry and ionospheric composition. An improved upper limit on CO in Plutos atmosphere is also reported.
Photometric variation of a directly imaged planet contains information on both the geography and spectra of the planetary surface. We propose a novel technique that disentangles the spatial and spectral information from the multi-band reflected light curve. This will enable us to compose a two-dimensional map of the surface composition of a planet with no prior assumption on the individual spectra, except for the number of independent surface components. We solve the unified inverse problem of the spin-orbit tomography and spectral unmixing by generalizing the non-negative matrix factorization (NMF) using a simplex volume minimization method. We evaluated our method on a toy cloudless Earth and observed that the new method could accurately retrieve the geography and unmix spectral components. Furthermore, our method is also applied to the real-color variability of the Earth as observed by Deep Space Climate Observatory (DSCOVR). The retrieved map explicitly depicts the actual geography of the Earth and unmixed spectra capture features of the ocean, continents, and clouds. It should be noted that, the two unmixed spectra consisting of the reproduced continents resemble those of soil and vegetation.
The Rosetta space probe accompanied comet 67P/Churyumov-Gerasimenko for more than two years, obtaining an unprecedented amount of unique data of the comet nucleus and inner coma. This work focuses identifying the source regions of faint jets and outbursts and on studying the spectrophotometric properties of some outbursts. We use observations acquired with the OSIRIS/NAC camera during July-October 2015, that is, close to perihelion. More than 200 jets of different intensities were identified directly on the nucleus. Some of the more intense outbursts appear spectrally bluer than the comet dark terrain in the vivible-to-near-infrared region. We attribute this spectral behavior to icy grains mixed with the ejected dust. Some of the jets have an extremely short lifetime. They appear on the cometary surface during the color sequence observations, and vanish in less than some few minutes after reaching their peak. We also report a resolved dust plume observed in May 2016 at a resolution of 55 cm/pixel, which allowed us to estimate an optical depth of $sim$0.65 and an ejected mass of $sim$ 2200 kg. We present the results on the location, duration, and colors of active sources on the nucleus of 67P from the medium-resolution (i.e., 6-10 m/pixel) images acquired close to perihelion passage. The observed jets are mainly located close to boundaries between different morphological regions. Jets depart not only from cliffs, but also from smooth and dust-covered areas, from fractures, pits, or cavities that cast shadows and favor the recondensation of volatiles. This study shows that faint jets or outbursts continuously contribute to the cometary activity close to perihelion passage, and that these events are triggered by illumination conditions. Faint jets or outbursts are not associated with a particular terrain type or morphology.
We present photometry and spectra of the large Kuiper belt object 2007 OR10. The data show significant near-infrared absorption features due to water ice. While most objects in the Kuiper belt with water ice absorption this prominent have the optically neutral colors of water ice, 2007 OR10 is among the reddest Kuiper belt objects known. One other large Kuiper belt object -- Quaoar -- has similar red coloring and water ice absorption, and it is hypothesized that the red coloration of this object is due to irradiation of the small amounts of methane able to be retained on Quaoar. 2007 OR10, though warmer than Quaoar, is in a similar volatile retention because it is sufficiently larger that its stronger gravity can still retain methane. We propose, therefore, that the red coloration on 2007 OR10 is also caused by the retention of small amounts of methane. Positive detection will require spectra of methane on 2007 OR10 will require spectra with higher signal-to-noise. Models for volatile retention on Kuiper belt objects appear to continue to do an excellent job reproducing all of the available observations.
The Neptunian satellite system is unusual. The major satellites of Jupiter, Saturn, and Uranus are all in prograde, low-inclination orbits. Neptune on the other hand, has the fewest satellites, and most of the systems mass is within one irregular satellite, Triton. Triton was most likely captured by Neptune and destroyed the primordial regular satellite system. We investigate the interactions between a newly captured Triton and a prior Neptunian satellite system. We find that a prior satellite system with a mass ratio similar to the Uranian system or smaller has a substantial likelihood of reproducing the current Neptunian system, while a more massive system has a low probability of leading to the current configuration. Moreover, Tritons interaction with a prior satellite system may offer a mechanism to decrease its high initial semimajor axis fast enough to preserve small irregular satellites (Nereid-like) that might otherwise be lost during a prolonged Triton circularization via tides alone.
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