101 research outputs found
Are NH and CO ice present on Miranda?
Published near-infrared spectra of the four largest classical Uranian
satellites display the presence of discrete deposits of CO ice, along with
subtle absorption features around 2.2 m. The two innermost satellites,
Miranda and Ariel, also possess surfaces heavily modified by past endogenic
activity. Previous observations of the smallest satellite, Miranda, have not
detected the presence of CO ice, and a report of an absorption feature at
2.2 m has not been confirmed. An absorption feature at 2.2 m could
result from exposed or emplaced NH- or NH-bearing species, which have a
limited lifetime on Miranda's surface, and therefore may imply that Miranda's
internal activity was relatively recent. In this work, we analyzed
near-infrared spectra of Miranda to determine whether CO ice and the
2.2-m feature are present. We measured the band area and depth of the
CO ice triplet (1.966, 2.012, and 2.070 m), a weak 2.13-m band
attributed to CO ice mixed with HO ice, and the 2.2-m band. We
confirmed a prior detection of a 2.2-m band on Miranda, but we found no
evidence for CO ice, either as discrete deposits or mixed with HO ice.
We compared a high signal-to-noise spectrum of Miranda to synthetic and
laboratory spectra of various candidate compounds to shed light on what species
may be responsible for the 2.2-m band. We conclude that the 2.2-m
absorption is best matched by a combination of NH ice with NH-hydrates
or NH-HO mixtures. NH-bearing salts like NHCl are also
promising candidates that warrant further investigation.Comment: 29 pages, 10 figures. Accepted for publication in Planetary Science
Journa
Abundance Measurements of Titan's Stratospheric HCN, HCN, CH, and CHCN from ALMA Observations
Previous investigations have employed more than 100 close observations of
Titan by the Cassini orbiter to elucidate connections between the production
and distribution of Titan's vast, organic-rich chemical inventory and its
atmospheric dynamics. However, as Titan transitions into northern summer, the
lack of incoming data from the Cassini orbiter presents a potential barrier to
the continued study of seasonal changes in Titan's atmosphere. In our previous
work (Thelen et al., 2018), we demonstrated that the Atacama Large
Millimeter/submillimeter Array (ALMA) is well suited for measurements of
Titan's atmosphere in the stratosphere and lower mesosphere (~100-500 km)
through the use of spatially resolved (beam sizes <1'') flux calibration
observations of Titan. Here, we derive vertical abundance profiles of four of
Titan's trace atmospheric species from the same 3 independent spatial regions
across Titan's disk during the same epoch (2012 to 2015): HCN, HCN,
CH, and CHCN. We find that Titan's minor constituents exhibit large
latitudinal variations, with enhanced abundances at high latitudes compared to
equatorial measurements; this includes CHCN, which eluded previous
detection by Cassini in the stratosphere, and thus spatially resolved abundance
measurements were unattainable. Even over the short 3-year period, vertical
profiles and integrated emission maps of these molecules allow us to observe
temporal changes in Titan's atmospheric circulation during northern spring. Our
derived abundance profiles are comparable to contemporary measurements from
Cassini infrared observations, and we find additional evidence for subsidence
of enriched air onto Titan's south pole during this time period. Continued
observations of Titan with ALMA beyond the summer solstice will enable further
study of how Titan's atmospheric composition and dynamics respond to seasonal
changes.Comment: 15 pages, 16 figures, 2 tables. Accepted for publication in Icarus,
September 201
Jovian Chromophore Characteristics from Multispectral HST Images
The chromophores responsible for coloring the jovian atmosphere are embedded within Jupiter's vertical aerosol structure. Sunlight propagates through this vertical distribution of aerosol particles, whose colors are defined by omega-bar (sub 0)(lambda), and we remotely observe the culmination of the radiative transfer as I/F(lambda). In this study, we employed a radiative transfer code to retrieve omega-bar (sub 0)(lambda) for particles in Jupiter's tropospheric haze at seven wavelengths in the near-UV and visible regimes. The data consisted of images of the 2008 passage of Oval BA to the south of the Great Red Spot obtained by the Wide Field Planetary Camera 2 on-board the Hubble Space Telescope. We present derived particle colors for locations that were selected from 14 weather regions, which spanned a large range of observed colors. All omega-bar (sub 0)(lambda) curves were absorbing in the blue, and omega-bar (sub 0)(lambda) increased monotonically to approximately unity as wavelength increased. We found accurate fits to all omega-bar (sub 0)(lambda) curves using an empirically derived functional form: omega-bar (sub 0)(lambda) = 1 A exp(-B lambda). The best-fit parameters for the mean omega-bar (sub 0)(lambda) curve were A = 25.4 and B = 0.0149 for lambda in units of nm. We performed a principal component analysis (PCA) on our omega-bar (sub 0)(lambda) results and found that one or two independent chromophores were sufficient to produce the variations in omega-bar (sub 0)(lambda). A PCA of I/F(lambda) for the same jovian locations resulted in principal components (PCs) with roughly the same variances as the omega-bar (sub 0)(lambda) PCA, but they did not result in a one-to-one mapping of PC amplitudes between the omega-bar (sub 0)(lambda) PCA and I/F(lambda) PCA. We suggest that statistical analyses performed on I/ F(lambda) image cubes have limited applicability to the characterization of chromophores in the jovian atmosphere due to the sensitivity of 1/ F(lambda) to horizontal variations in the vertical aerosol distribution
A Europa CubeSat Concept Study for Measuring Europa\u27s Atmosphere
This presentation is the product of a nine-month mission concept study for a CubeSat that would be carried aboard the JPL Europa Multiple-Flyby Mission, released in the Jovian system and make measurements at Europa. We examined the scientific return as well as the technical feasibility of a CubeSat designed to study the linkage between Europa\u27s radiation environment which generates Europa\u27s atmosphere through sputtering and radiolytic processes, and its atmospheric structure. This would be accomplished by measuring a) energetic particles at Europa and b) its atmospheric density through drag forces on the CubeSat. The findings of our concept study for the Deployable Atmospheric Reconnaissance CubeSat with Sputtering Ion Detector at Europa (DARCSIDE) indicate that the technology exists to enable a 3U, 4.4 kg CubeSat to detect Europa\u27s tenuous atmosphere beginning ~200 km above the surface for ~400 s of flight time during a single flyby, by measuring drag on the vehicle. By including a charged particle detector, we can also measure the sputtering-induced charged particle flux incident on Europa\u27s surface - either for a single arc across the surface or for a number of predeployment Jovian orbits while onboard the Europa Multiple-Flyby Mission - depending on the length of time the instrument is powered on. In addition to providing highly complementary science to the Europa Multiple-Flyby Mission, the combination of the accelerometer and charged particle detector will yield important insights for the study of Europa\u27s atmosphere and surface composition, its interaction with the Jovian magnetosphere, and possibly links to its subsurface ocean.
This presentation will be focused on the technical challenges of the DARCSIDE mission. The major challenges to be discussed will include how to survive with only one twenty-fifth the energy available at the Earth, this has significant implications for spacecraft temperature and electrical power generation. Additionally, survival in the extreme Jovian radiation environment will be discussed, along how to meet planetary protection requirements for Europa, which requires DARCSIDE to never impact Europa. Finally, the design for the DARCSIDE drag system, and accelerometers will be discussed
L-Band Photometry of L and T Dwarfs
We present K- and L-band photometry obtained with the Keck I telescope for a
representative sample of L and T dwarfs. These observations were motivated in
part by the dominant role water and methane play in shaping the flux near 2 and
3 microns and by the potential use of these bands as indicators of spectral
class in the infrared. In addition, these observations aid the determination of
the bolometric luminosity of L and T dwarfs. Here we report the K, L' and Ls
magnitudes of our objects and the trends observed in the (K-L') and (K-Ls)
colors as a function of L- and T-dwarf spectral class. We compare these colors
with theoretical models, derive a relationship between effective temperature
and L-spectral class, and compare our temperature estimates with others.Comment: Paper to be published in ApJL, 15 pages, 3 figure
Solar System Observations with the James Webb Space Telescope
The James Webb Space Telescope will enable a wealth of new scientific
investigations in the near- and mid-infrared, with sensitivity and
spatial/spectral resolution greatly surpassing its predecessors. In this paper,
we focus upon Solar System science facilitated by JWST, discussing the most
current information available concerning JWST instrument properties and
observing techniques relevant to planetary science. We also present numerous
example observing scenarios for a wide variety of Solar System targets to
illustrate the potential of JWST science to the Solar System community. This
paper updates and supersedes the Solar System white paper published by the JWST
Project in 2010 (Lunine et al., 2010). It is based both on that paper and on a
workshop held at the annual meeting of the Division for Planetary Sciences in
Reno, NV in 2012.Comment: 52 pages (with figures), 32 figures; More information about JWST
Solar System observations is available at
http://www.stsci.edu/jwst/science/solar-syste
Rotational Variation of Daughter Species Production Rates in Comet 103P/Hartley: Implications for the Progeny of Daughter Species and the Degree of Chemical Heterogeneity
We present analysis of high spectral resolution optical spectra of Comet 103P/Hartley taken during its Fall 2010 apparition. These spectra include transitions belonging to CN, C2, CH, NH2, and OI. We measure production rates and mixing ratios from these spectra. We find evidence for large changes in production rates (factors of a few) over the course of a nucleus rotation, in agreement with other measurements. We also measure variability with rotational phase in the CN/H2O and C2/CN ratios, which has not been previously reported for any comet. There may also be variability in the NH2/H2O ratio with rotational phase, but this trend is not as clear as for CN/H2O. We interpret the changing mixing ratios as due to H2O and C2 being released primarily from the icy grain halo, while the CN parent molecule comes directly from the nucleus. There is evidence that the CH/CN ratio is higher pre-perihelion than post-perihelion. We conclude that the observed CN and NH2 abundances are consistent with HCN and NH3 being the dominant parent molecules for these species. The C2 and CH abundances are higher than those of candidate parent molecules (C2H2 and CH4 respectively), so there must be another source for these molecules in 103P's coma. Carbonaceous dust grains could serve as this source
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