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A. Coustenis,
S. K. Atreya,
T. Balint,
R. H. Brown,
M. K. Dougherty,
F. Ferri,
M. Fulchignoni,
D. Gautier,
R. A. Gowen,
C. A. Griffith, [......],
C. Szopa,
R. Thissen,
M. G. Tomasko,
D. Toublanc,
H. Vali,
I. Vardavas,
V. Vuitton,
R. A. West,
R. Yelle, E. F. Young
[show abstract]
[hide abstract]
ABSTRACT: TandEM was proposed as an L-class (large) mission in response to ESA’s Cosmic Vision 2015–2025 Call, and accepted for further
studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds
tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini–Huygens
mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM
is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is
designed to build on but exceed the scientific and technological accomplishments of the Cassini–Huygens mission, exploring
Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time).
In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft
would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators
to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in
situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through
the atmosphere.
Experimental Astronomy 04/2012; 23(3):893-946. · 1.82 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: 1] The variability of temperature and salinity in the Irish Sea over the 40 year period 1960–1999 is investigated using a free-running fine-resolution local area model. The skill of the model to represent observed temperature and salinity variability is assessed using conductivity-temperature-depth survey data (3397 profiles) and a long time series of measurements from Cypris station (southwest of Isle of Man). This clearly demonstrates that the model can reproduce the observed seasonal and longer-term cycles in temperature, with mean and RMS errors of À0.01°C and 0.78°C. Particularly apparent is the long-term warming trend at Cypris station and throughout the model domain. Model estimates of salinity are less accurate and are generally too saline (mean and RMS errors are 0.79 and 0.98 practical salinity units). Inaccuracies are likely to arise from boundary conditions and forcing (riverine and surface). However, while absolute values are not particularly well represented, the model reproduces many of the trends in the salinity variability observed at Cypris station, suggesting that the dominant physical processes in the Irish Sea, with timescales up to $3 years, are well represented. The model is also used to investigate the variability in temperature stratification. While stratification is confined to approximately the same geographical area in each year of the simulation, there is significant variability in the timing of the onset and breakdown of stratification and in the peak surface to bed temperature difference. Together, these results suggest that a local area model with limited boundary conditions may be sufficiently accurate for climatic investigation of some (locally forced) parameters.
J. Geophys. Res. 01/2007; 112.
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[hide abstract]
ABSTRACT: We have made near-IR spectral observations of the very young (5.75 Myr) S-type asteroid 832 Karin, well sampled in rotational phase over its 18.35-h period. We find no significant variations in its reflectance spectrum. Karin, the brightest member of the Karin cluster (a sub-family of the larger, older Koronis dynamical family), was shown to be exceptionally young by Nesvorný et al.722], using backward numerical integration of orbital elements of cluster members. Their precise dating of the collisional breakup gives us an opportunity, for the first time and without age-dating of physical samples, to monitor time-evolution of processes, like space weathering, that operate on timescales of ∼1–10 Myr. Sasaki et al. Abstract #1590] had made similar measurements of Karin, although more sparsely sampled than ours, and claimed dramatically different colors as a function of rotational phase. Sasaki et al. interpreted their data to be showing the reddish, space-weathered exterior surface of the precursor asteroid, as well as an interior face, which had not had time to become space-weathered. On five nights over 2006 January 7–14 UT, we observed Karin with the SpeX (0.8–2.5 µm) spectrometer of the IRTF. We analyze data in 30 • intervals of rotational longitude, some of which we sampled on two different nights. The spectra are consistent with little or no spectral variation as the asteroid rotates; certainly there are no changes as large as previously reported. The previous observations were probably spurious. Our average spectrum resembles the "blue" spectrum of Sasaki et al., which they interpreted to be the "fresh" surface. Karin is not quite as red as typical S-types, yet has rather shallow absorption bands. We surmise that the space-weathering process affecting Karin has had time to reduce spectral contrast, but has not operated long enough to redden its spectrum—an intermediate case of space weathering, which has gone to completion for most main-belt asteroids. This work sets an important constraint on the timescale for the ubiquitous space-weathering process affecting S-types, namely that its effects are evident, but not yet complete, at ∼6 Myr.
Nature Astrophys. J. Lunar Planet. Sci. XXXVI. 01/2002; 417(615):720-161.
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[show abstract]
[hide abstract]
ABSTRACT: We observed Titan with the Hubble Space Telescope in November 2000 using the Wide-Field Plane-tary Camera (WFPC2) and the Space Telescope Imaging Spectrograph (STIS). Considerable change is apparent be-tween these and observations in 1994-1997 : in particular the North-South asymmetry at visible wavelengths has re-versed, with the southern hemisphere brighter, as during the Voyager epoch. The asymmetry shows considerable varia-tion with wavelength in the near-infrared : in the 889nm methane band the asymmetry (which formerly resembled a 'smile') has reversed in the last 3 years, while at 953nm the southern limb is still bright. A south polar collar, dark at ultraviolet wavelengths, is apparent some five years after equinox.
01/2001; 28(1):4453-4456.
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08/1999; 31:1137.
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[hide abstract]
ABSTRACT: Until relatively recent advances in technology, astronomical observations from the ground were limited in image resolution by the blurring effects of earth's atmosphere. The blur extent, ranging typically from 0.5 to 2 seconds of arc at the best astronomical sights, precluded ground-based observations of the details of the solar system's moons, asteroids, and outermost planets. With the maturing of a high resolution image processing technique called speckle imaging the resolution limitation of the atmosphere can now be largely overcome. Over the past three years they have used speckle imaging to observe Titan, a moon of Saturn with an atmospheric density comparable to Earth's, Io, the volcanically active innermost moon of Jupiter, and Neptune, a gas giant outer planet which has continually changing planet-encircling storms. These observations were made at the world's largest telescope, the Keck telescope in Hawaii and represent the highest resolution infrared images of these objects ever taken.
02/1999;
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[hide abstract]
ABSTRACT: Titan's haze particles are the principle opacity at solar wavelengths.
Most past work in modeling these particles has assumed spherical
particles. However, observational evidence strongly favors fractal
shapes for the haze particles. We consider the implications of fractal
particles for the thermal structure and near infrared opacity of Titan's
atmosphere. We find that assuming fractal particles with the optical
properties based on laboratory tholin material and with a production
rate that allows for a match to the geometric albedo results in warmer
troposphere and surface temperatures compared to spherical particles. In
the near infrared (1-3 microns) the predicted opacity of the fractal
particles is up to a factor of two less than for spherical particles.
This has implications for the ability of Cassini to image Titan's
surface at 1 micron.
08/1998; 30:1091.
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31:1136.
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[hide abstract]
ABSTRACT: We present results from 14 nights of observations of Titan in 1996–1998 using near-infrared (centered at 2.1 microns) speckle imaging at the 10-meter W.M. Keck Telescope. The observations have a spatial resolution of 0.06 arcseconds. We detect bright clouds on three days in October 1998, with a brightness about 0.5% of the brightness of Titan. Using a 16-stream radiative transfer model (DISORT) to model the central equatorial longitude of each image, we construct a suite of surface albedo models parameterized by the optical depth of Titan's hydrocarbon haze layer. From this we conclude that Titan's equatorial surface albedo has plausible values in the range of 0–0.20. Titan's minimum haze optical depth cannot be constrained from this modeling, but an upper limit of 0.3 at this wavelength range is found. More accurate determination of Titan's surface albedo and haze optical depth, especially at higher latitudes, will require a model that fully considers the 3-dimensional nature of Titan's atmosphere.
Icarus.
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[show abstract]
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ABSTRACT: Saturn's large moon Titan is unique among planetary satellites in that it possesses a thick atmosphere and a haze layer that is opaque to visible light. This haze is believed to be composed of organic compounds produced by the photolysis of methane. It has been suggested that the photochemical products of methane photolysis, primarily ethane, would “rain out” over time and may produce reservoirs of liquid hydrocarbons on Titan's surface. Such material would appear very dark, with an albedo ≤0.02 (Khare et al. 1990, Bull. Am. Astron. Soc.22, 1033). Such low-albedo regions have not been previously detected on Titan's surface. Here we report observations of Titan at a resolution of 0.04 arcsec (0.02 arcsec/pixel) using the technique of speckle imaging from the 10-m Keck I Telescope. By observing Titan at specific infrared wavelengths which are windows through its atmosphere, we have made both an albedo map of Titan's surface at 1.6 and 2.1 μm and an estimate of Titan's haze optical depth at these wavelengths. We clearly distinguish low-albedo features (reflectance <0.05) on Titan's surface.
Icarus.
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A. Coustenis,
S. K. Atreya,
T. Balint,
R H Brown,
M. K. Dougherty,
F. Ferri,
M. Fulchignoni,
D. Gautier,
R. A. Gowen,
C. A. Griffith, [......],
T. Haltigin,
O. Dutuit,
D. Fairbrother,
F. M. Flasar,
A D Fortes,
R. Frampton,
D. Luz,
A. Herique,
F. Hersant,
A. Milillo
[show abstract]
[hide abstract]
ABSTRACT: 54 pages, 8 figures.-- In press. TandEM was proposed as an L-class (large) mission in response to ESA’s Cosmic Vision 2015–2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini–Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini–Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmosphere. TandEM was proposed in response to ESA’s Cosmic Vision 2015–2025 Call. Peer reviewed
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A. Coustenis,
S. K. Atreya,
T. Balint,
R. H. Brown,
M. K. Dougherty,
F. Ferri,
M. Fulchignoni,
D. Gautier,
R. A. Gowen,
C. A. Griffith, [......],
C. Szopa,
R. Thissen,
M. G. Tomasko,
D. Toublanc,
H. Vali,
I. Vardavas,
V. Vuitton,
R. A. West,
R. Yelle, E. F. Young
[show abstract]
[hide abstract]
ABSTRACT: TandEM was proposed as an L-class (large) mission in response to ESA’s Cosmic Vision 2015–2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini–Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini–Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmosphere.
Experimental Astronomy. 23(2009):893-946.
