46 research outputs found
Titan's Prolific Propane: The Cassini CIRS Perspective
In this paper we select large spectral averages of data from the Cassini
Composite Infrared Spectrometer (CIRS) obtained in limb-viewing mode at low
latitudes (30S--30N), greatly increasing the path length and hence
signal-to-noise ratio for optically thin trace species such as propane. By
modeling and subtracting the emissions of other gas species, we demonstrate
that at least six infrared bands of propane are detected by CIRS, including two
not previously identified in Titan spectra. Using a new line list for the range
1300-1400cm -1, along with an existing GEISA list, we retrieve propane
abundances from two bands at 748 and 1376 cm-1. At 748 cm-1 we retrieve 4.2 +/-
0.5 x 10(-7) (1-sigma error) at 2 mbar, in good agreement with previous
studies, although lack of hotbands in the present spectral atlas remains a
problem. We also determine 5.7 +/- 0.8 x 10(-7) at 2 mbar from the 1376 cm-1
band - a value that is probably affected by systematic errors including
continuum gradients due to haze and also an imperfect model of the n6 band of
ethane. This study clearly shows for the first time the ubiquity of propane's
emission bands across the thermal infrared spectrum of Titan, and points to an
urgent need for further laboratory spectroscopy work, both to provide the line
positions and intensities needed to model these bands, and also to further
characterize haze spectral opacity. The present lack of accurate modeling
capability for propane is an impediment not only for the measurement of propane
itself, but also for the search for the emissions of new molecules in many
spectral regions.Comment: 7 Figures, 3 Tables. Typeset in Latex with elsart.cls. In press for
Planetary and Space Scienc
The Seismic Moment and Seismic Efficiency of Small Impacts on Mars
Since landing in late 2018, the InSight lander has been recording seismic signals on the surface of Mars. Despite nominal prelanding estimates of one to three meteorite impacts detected per Earth year, none have yet been identified seismically. To inform revised detectability estimates, we simulated numerically a suite of small impacts onto Martian regolith and characterized their seismic source properties. For the impactor size and velocity range most relevant for InSight, crater diameters are 1â30 m. We found that in this range scalar seismic moment is 106â1010 Nm and increases almost linearly with impact momentum. The ratio of horizontal to vertical seismic moment tensor components is âŒ1, implying an almost isotropic P wave source, for vertical impacts. Seismic efficiencies are âŒ10â6, dependent on the target crushing strength and impact velocity. Our predictions of relatively low seismic efficiency and seismic moment suggest that meteorite impact detectability on Mars is lower than previously assumed. Detection chances are best for impacts forming craters of diameter >10 m
Titan's stratospheric C2N2, C3H4, and C4H2 abundances from Cassini/CIRS far-infrared spectra
Seismic Coupling of Short-Period Wind Noise Through Marsâ Regolith for NASAâs InSight Lander
Time variability of Neptuneâs horizontal and vertical cloud structure revealed by VLT/SINFONI and Gemini/NIFS from 2009 to 2013
An Autonomous Lunar Geophysical Experiment Package (ALGEP) for future space missions
Geophysical observations will provide key information about the inner structure of the planets and satellites and understanding the internal structure is a strong constraint on the bulk composition and thermal evolution of these bodies. Thus, geophysical observations are a key to uncovering the origin and evolution of the Moon. In this article, we propose the development of an autonomous lunar geophysical experiment package, composed of a suite of instruments and a central station with standardized interface, which can be installed on various future lunar missions. By fixing the interface between instruments and the central station, it would be possible to easily configure an appropriate experiment package for different missions. We describe here a series of geophysical instruments that may be included as part of the geophysical package: a seismometer, a magnetometer, a heat flow probe, and a laser reflector. These instruments will provide mechanical, thermal, and geodetic parameters of the Moon that are strongly related to the internal structure. We discuss the functionality required for future geophysical observations of the Moon, including the development of the central station that will be used commonly by different payloads
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Water Vapor Vertical Profiles on Mars in Dust Storms Observed by TGO/NOMAD
It has been suggested that dust storms efficiently transport water vapor from the nearâsurface to the middle atmosphere on Mars. Knowledge of the water vapor vertical profile during dust storms is important to understand water escape. During Martian Year 34, two dust storms occurred on Mars: a global dust storm (June to midâSeptember 2018) and a regional storm (January 2019). Here we present water vapor vertical profiles in the periods of the two dust storms (Ls = 162â260° and Ls = 298â345°) from the solar occultation measurements by Nadir and Occultation for Mars Discovery (NOMAD) onboard ExoMars Trace Gas Orbiter (TGO). We show a significant increase of water vapor abundance in the middle atmosphere (40â100 km) during the global dust storm. The water enhancement rapidly occurs following the onset of the storm (Ls~190°) and has a peak at the most active period (Ls~200°). Water vapor reaches very high altitudes (up to 100 km) with a volume mixing ratio of ~50 ppm. The water vapor abundance in the middle atmosphere shows high values consistently at 60°Sâ60°N at the growth phase of the dust storm (Ls = 195°â220°), and peaks at latitudes greater than 60°S at the decay phase (Ls = 220°â260°). This is explained by the seasonal change of meridional circulation: from equinoctial Hadley circulation (two cells) to the solstitial one (a single poleâtoâpole cell). We also find a conspicuous increase of water vapor density in the middle atmosphere at the period of the regional dust storm (Ls = 322â327°), in particular at latitudes greater than 60°S
Topographic, spectral and thermal inertia analysis of interior layered deposits in Iani Chaos, Mars
We present an analysis of Interior Layered Deposits (ILDs) in Iani Chaos using visible, infrared, hyperspectral and topographic datasets acquired by instruments aboard NASAâs Mars Global Surveyor, Mars Odyssey, Mars Reconnaissance Orbiter and ESAâs Mars Express spacecraft. We focus on four main regions where ILDs outcrop in Iani Chaos. Deposits span a âŒ2 km range of elevations and exhibit moderate to high albedos, layering at sub-decameter scales, thermal inertias of 300â800 J mâ2 Kâ1 sâ1/2 and a range of surface textures. Thermal inertia calculations use slope and azimuth corrections from High Resolution Stereo Camera (HRSC) topography. Spectral features in hyperspectral data acquired by NASAâs Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) suggest that gypsum (CaSO4·2H2O) and kieserite (MgSO4·H2O) are present in most deposits. We report absorptions typically exhibited by alunite (KAl3(SO4)2(OH)6) and jarosite View the MathML sourceKFe33+(OH)6(SO4)2 as well as a number of features that may be attributable to a wide range of mono- and polyhydrated sulphates and hydroxyl-sulphates bearing a number of cations, including Mg2+, Fe2+, Fe3+ and Ca2+. Spectral features similar to those of ammonium sulphates may also be present.
Analysis of a HiRISE stereo DEM shows planar layering in some ILDs, favouring a sedimentary deposition origin. Stratigraphic mapping of hydration and sulphate spectral features in flat ILDs in central Iani Chaos suggest that specific elevation intervals in the stratigraphic column were subject to different levels of hydration, perhaps during episodes of water table elevation. This is consistent with formation models for ILDs and hydrological modelling. Geomorphic characteristics of deposits in northern and southern Iani Chaos suggest their relatively recent exhumation and significant erosion by aeolian processes. We conclude that any formation theory for ILDs in Iani Chaos should support mechanisms for different hydration states at different stratigraphic elevations and subsequent significant aeolian erosion, burial and re-exposure