1,073 research outputs found
The fate of ethane in Titan's hydrocarbon lakes and seas
Ethane is expected to be the dominant photochemical product on Titan's
surface and, in the absence of a process that sequesters it from exposed
surface reservoirs, a major constituent of its lakes and seas. Absorption of
Cassini's 2.2 cm radar by Ligeia Mare however suggests that this north polar
sea is dominated by methane. In order to explain this apparent ethane
deficiency, we explore the possibility that Ligeia Mare is the visible part of
an alkanofer that interacted with an underlying clathrate layer and investigate
the influence of this interaction on an assumed initial ethane-methane mixture
in the liquid phase. We find that progressive liquid entrapment in clathrate
allows the surface liquid reservoir to become methane-dominated for any initial
ethane mole fraction below 0.75. If interactions between alkanofers and
clathrates are common on Titan, this should lead to the emergence of many
methane-dominated seas or lakes.Comment: Accepted for publication in Icaru
Discovery of seven volcanic outbursts on Io from an IRTF observation campaign 2016 to 2022
This study analyzes near-infrared measurements of Io, Jupiter's moon,
observed over 170 nights from 2016 to early 2022 using the NASA Infrared
Telescope Facility (IRTF). During this period, seven new volcanic outbursts,
the most energetic volcanic events on Io, were discovered and characterized,
increasing the total number of observed outburst events from 18 to 25. We also
present simplified criteria for the thermal detection of an outburst, requiring
it to be both confined to a specific location of Io and above a threshold
intensity in the Lp-band (3.8 micron).
Our measurements use 2 to 5 micron photometry in eclipse, Jupiter
occultation, and reflected sunlight. In addition to extending the observational
dataset of Io's dynamic activity, these data provide insights into the temporal
and spatial distribution of outbursts on Io. Notably, all seven outbursts were
detected in Io's trailing hemisphere. These include Pillan Patera and a newly
discovered repeating outburst location at Acala Fluctus. We add these events to
the rare category of recurring outbursts, before which Tvashtar was the only
known example. We observed that another outburst at UP 254W decreased in
Lp-band intensity by a factor of two in 4.5 hours. In August 2021, Io exhibited
high volcanic activity when two powerful outbursts rapidly appeared,
propagating East. Our findings underscore IRTF's ongoing contributions to the
study of Io
Insights into Titan’s geology and hydrology based on enhanced image processing of Cassini RADAR data
The Cassini Synthetic Aperture Radar has been acquiring images of Titan's surface since October 2004. To date, 59% of Titan's surface has been imaged by radar, with significant regions imaged more than once. Radar data suffer from speckle noise hindering interpretation of small-scale features and comparison of reimaged regions for change detection. We present here a new image analysis technique that combines a denoising algorithm with mapping and quantitative measurements that greatly enhance the utility of the data and offers previously unattainable insights. After validating the technique, we demonstrate the potential improvement in understanding of surface processes on Titan and defining global mapping units, focusing on specific landforms including lakes, dunes, mountains, and fluvial features. Lake shorelines are delineated with greater accuracy. Previously unrecognized dissection by fluvial channels emerges beneath shallow methane cover. Dune wavelengths and interdune extents are more precisely measured. A significant refinement in producing digital elevation models is shown. Interactions of fluvial and aeolian processes with topographic relief is more precisely observed and understood than previously. Benches in bathymetry are observed in northern sea Ligeia Mare. Submerged valleys show similar depth suggesting that they are equilibrated with marine benches. These new observations suggest a liquid level increase in the northern sea, which may be due to changes on seasonal or longer timescales
Titan Science with the James Webb Space Telescope (JWST)
The James Webb Space Telescope (JWST), scheduled for launch in 2018, is the
successor to the Hubble Space Telescope (HST) but with a significantly larger
aperture (6.5 m) and advanced instrumentation focusing on infrared science
(0.6-28.0 m ). In this paper we examine the potential for scientific
investigation of Titan using JWST, primarily with three of the four
instruments: NIRSpec, NIRCam and MIRI, noting that science with NIRISS will be
complementary. Five core scientific themes are identified: (i) surface (ii)
tropospheric clouds (iii) tropospheric gases (iv) stratospheric composition and
(v) stratospheric hazes. We discuss each theme in depth, including the
scientific purpose, capabilities and limitations of the instrument suite, and
suggested observing schemes. We pay particular attention to saturation, which
is a problem for all three instruments, but may be alleviated for NIRCam
through use of selecting small sub-arrays of the detectors - sufficient to
encompass Titan, but with significantly faster read-out times. We find that
JWST has very significant potential for advancing Titan science, with a
spectral resolution exceeding the Cassini instrument suite at near-infrared
wavelengths, and a spatial resolution exceeding HST at the same wavelengths. In
particular, JWST will be valuable for time-domain monitoring of Titan, given a
five to ten year expected lifetime for the observatory, for example monitoring
the seasonal appearance of clouds. JWST observations in the post-Cassini period
will complement those of other large facilities such as HST, ALMA, SOFIA and
next-generation ground-based telescopes (TMT, GMT, EELT).Comment: 50 pages, including 22 figures and 2 table
On line power spectra identification and whitening for the noise in interferometric gravitational wave detectors
In this paper we address both to the problem of identifying the noise Power
Spectral Density of interferometric detectors by parametric techniques and to
the problem of the whitening procedure of the sequence of data. We will
concentrate the study on a Power Spectral Density like the one of the
Italian-French detector VIRGO and we show that with a reasonable finite number
of parameters we succeed in modeling a spectrum like the theoretical one of
VIRGO, reproducing all its features. We propose also the use of adaptive
techniques to identify and to whiten on line the data of interferometric
detectors. We analyze the behavior of the adaptive techniques in the field of
stochastic gradient and in the
Least Squares ones.Comment: 28 pages, 21 figures, uses iopart.cls accepted for pubblication on
Classical and Quantum Gravit
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