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
Experimental Astronomy 04/2012; 23(3):893-946. · 1.82 Impact Factor
grl. 12/2011; 38:23201.
Nature Geoscience 11/2011; 4:750-752. · 11.75 Impact Factor
ABSTRACT: Although there is evidence that liquids have flowed on the surface at Titan's equator in the past, to date, liquids have only been confirmed on the surface at polar latitudes, and the vast expanses of dunes that dominate Titan's equatorial regions require a predominantly arid climate. We report the detection by Cassini's Imaging Science Subsystem of a large low-latitude cloud system early in Titan's northern spring and extensive surface changes (spanning more than 500,000 square kilometers) in the wake of this storm. The changes are most consistent with widespread methane rainfall reaching the surface, which suggests that the dry channels observed at Titan's low latitudes are carved by seasonal precipitation.
Science 03/2011; 331(6023):1414-7. · 31.20 Impact Factor
ABSTRACT: Since Cassini's arrival at Saturn the season has progressed from
northern winter to just past the northern vernal equinox (the equivalent
of ~mid-January to late March on Earth), driving changes in the weather
patterns. Until shortly after Cassini arrived at Saturn, large
convective cloud systems were common over the South Pole. Since 2005,
such storms have been less common and elongated streaks of clouds have
been observed further and further to the north, becoming common at high
northern latitudes by 2007. Cassini's Imaging Science Subsystem (ISS)
has also observed changes in surface features at high southern
latitudes: a new large dark area appeared between July 2004 and June
2005 and may have subsequently faded; recent observations of Ontario
Lacus suggest that its boundary may have receded somewhat as well. Such
changes are interpreted to be the result of precipitation and ponding of
liquid methane and the subsequent evaporation thereof. Intriguingly,
Cassini RADAR observations of areas near Titan's south pole reveal far
fewer lakes than are observed by RADAR at high northern latitudes and
fewer than suggested by the number of dark features observed by ISS in
this area. This apparent discrepancy may simply be a result of the fact
that not all dark features identified by ISS are liquid-filled; however
another possible explanation is that evaporation has occurred between
the ISS observations in mid-2005 and RADAR observations of similar
territory starting in 2007. Further investigation of comparison of ISS
and RADAR observations is underway to better understand the implications
of the differences observed. We will present observations of Titan's
atmospheric behavior and surface features, documenting changes that have
resulted from weather and seasonal change.
AGU Fall Meeting Abstracts. 11/2009; -1:01.
ABSTRACT: ISS observations suggest that Titan's South Pole harbors surface
reservoirs of liquid hydrocarbons, as have also been observed at high
northern latitudes. The images provide information on the size and
spatial distributions of Titan's lakes and seas.
ABSTRACT: The Cassini orbiter's Visual & Infrared Mapping Spectrometer (VIMS)
observes Titan's surface intensity at wavelengths where its methane-rich
atmosphere is heavily absorbing and light is strongly scattering.
Therefore, most analyses of Titan's surface that require use of the VIMS
dataset (e.g., photoclinometry, geologic interpretation, spectral
identification of surface materials, photometry) are impeded until a
method to separate the atmospheric from the surface spectral signature
of Titan is fully developed. In a previous work (Pitman et al.
2007,AAS-DPS meeting #39), we presented a fully-functional
plane-parallel radiative transfer (RT) correction method with core
components extended from Mars surface-atmospheric separation models that
can be used for modeling and removing Titan's atmosphere for VIMS
observations which are far from the limb. This "Mars/Titan" hybrid
plane-parallel RT correction model includes inputs from Cassini-Huygens
c. 2007, allows for vertical variation of major atmospheric properties,
and incorporates newly released methane absorption coefficients and haze
scattering properties derived from in situ measurements by the Huygens
DISR team. In this work, we attempt to resolve the issue of atmospheric
variation as a function of Titan's geographic coordinates by utilizing a
spherical-shell radiative transfer model, originally used by Cassini
engineers to model radiation flow through Titan's atmosphere and used by
other Cassini teams for atmospheric correction as well. Trade-offs on
when and where to use which type of model will be discussed. Work
performed under contract to NASA and under appointment to the NASA
Postdoctoral Program (ORAU).
AGU Fall Meeting Abstracts. 11/2007; -1:1357.
ABSTRACT: The gases in the plumes include H2O, CO2,
N2, CH4, and possibly other hydrocarbons,
according to the INMS team. The solid particles in the plumes are
probably water ice, but the identification is less certain than for the
gaseous components. The plumes emanate from warm cracks in the surface
near the south pole. The gas has a scale height of 80 km, according to
the UVIS team, and the particles have a scale height of 30 km, according
to the ISS team. By integrating across the plumes in their images, the
ISS team was able to infer the upward flux of particles vs. altitude.
Close to the surface, the falloff of density with altitude is much
steeper than that of an escaping atmosphere in which both the particles
and the gas are moving upward with the thermal velocity of the gas. Thus
some of the particles are falling back to the surface and some are
escaping. The larger scale height of the gas implies that the escaping
fraction is greater for the gas. I will present models that attempt to
explain these plume data. The density of the gas and the size of the
particles determine the degree of dynamical coupling between gas and
particles. There are three models - a sublimating gas that picks up
particles as it leaves the surface; sublimating gas that forms particles
in flight as the pressure decreases; a boiling liquid that freezes by
evaporative cooling as the pressure decreases. Each model has its own
range of mass flux, density, particle size, and scale height for both
gas and liquid. I will discuss the implications of the observations and
models regarding the possibility of liquid water near the surface.
ABSTRACT: 1] Multifilter images of Jupiter acquired by the Cassini Imaging Science Subsystem (ISS) are used to derive zonal winds at altitudes above and below the visible cloud deck. Small features unique to the ultraviolet images of ISS are tracked to get the systematic high-altitude zonal winds. Comparison between the zonal winds from ultraviolet images and the vertical profile of zonal winds from the Cassini Composite Infrared Spectrometer (CIRS) shows that the zonal winds from the ultraviolet images are from a pressure level that is $0.2 scale heights higher than the pressure level of the zonal winds from continuum-band images. Deeper zonal winds at different latitudes of the equatorial region are measured by tracking cloud features observed within hot spots on continuum-band images. The deeper zonal winds in this study extend the measurement of the Galileo probe to different latitudes of the equatorial region. Comparison between the Galileo probe and this study suggests that these fast-moving clouds within hot spots are deeper than 3 bars and are therefore probably water clouds.
J. Geophys. Res. 01/2006; 111.
ABSTRACT: Titan is the only satellite in our Solar System with a substantial atmosphere, the origins and evolution of which are still not well understood. Its primary (greater than 90%) component is nitrogen, with a few percent methane and lesser amounts of other species. Methane and ethane are stable in the liquid state under the temperature and pressure conditions in Titan s lower atmosphere and at the surface; indeed, clouds, likely composed of methane, have been detected. Photochemical processes acting in the atmosphere convert methane into more complex hydrocarbons, creating Titan s haze and destroying methane over relatively short timescales. Therefore, it has been hypothesized that Titan s surface has reservoirs of liquid methane which serve to resupply the atmosphere. Early observations of Titan s surface revealed albedo patterns which have been interpreted as dark hydrocarbon liquids occupying topographically low regions between higher-standing exposures of bright, water-ice bedrock, although this is far from being the only explanation for the observed albedo contrast. Observations made by the Imaging Science Subsystem during Cassini's approach to Saturn and its first encounters with Titan show the bright and dark regions in greater detail but have yet to resolve the question of whether there are liquids on the surface.
ABSTRACT: Cassini's Imaging Science Subsystem (ISS) instrument took nearly 1200 images of the Jupiter ring system during the spacecraft's 6-month encounter with Jupiter (Porco et al., 2003, Science 299, 1541–1547). These observations constitute the most complete data set of the ring taken by a single instrument, both in phase angle (0.5 • –120 • at seven angles) and wavelength (0.45–0.93 µm through eight filters). The main ring was detected in all targeted exposures; the halo and gossamer rings were too faint to be detected above the planet's stray light. The optical depth and radial profile of the main ring are consistent with previous observations. No broad asymmetries within the ring were seen; we did identify possible hints of 1000 km-scale azimuthal clumps within the ring. Cassini observations taken within 0.02 • of the ring plane place an upper limit on the ring's full thickness of 80 km at a phase angle of 64 • . We have combined the Cassini ISS and VIMS (Visible and Infrared Mapping Spectrometer) observations with those from Voyager, HST (Hubble Space Telescope), Keck, Galileo, Palomar, and IRTF (Infrared Telescope Facility). We have fit the entire suite of data using a photometric model that includes microscopic silicate dust grains as well as larger, long-lived 'parent bodies' that engender this dust. Our best-fit model to all the data indicates an optical depth of small particles of τ s = 4.7 × 10 −6 and large bodies τ l = 1.3 × 10 −6 . The dust's cross-sectional area peaks near 15 µm. The data are fit significantly better using non-spherical rather than spherical dust grains. The parent bodies themselves must be very red from 0.4–2.5 µm, and may have absorption features near 0.8 and 2.2 µm.
Icarus 01/2004; 172:59-77. · 3.38 Impact Factor
ABSTRACT: Two basic models developed to support the design of the descent imager/spectral radiometer into Titan's atmosphere are summarized. During the development of Huygens optical instruments for Titan's atmospheric descent, models of sunlight penetration into the atmosphere were required. Huygens is the ESA contribution to the NASA/ESA Cassini/Huygens mission to Saturn and Titan. The mission is scheduled for November 2004. Huygens is an atmospheric probe designed to study the atmosphere and surface of Titan. The wavelength and altitude dependent parameters used for the two models show their ability to reproduce a variety of observational constraints, and indicate the downward direct, downward diffuse and upward fluxes of sunlight as functions of altitude throughout Titan's atmosphere for both models.
ABSTRACT: The Huygens probe payload includes the descent imager/spectral radiometer (DISR). The design and operation of the DISR optical instrument, including its major science and data expected from its descent into Titan's atmosphere are given. Huygens is the ESA contribution to the NASA/ESA Cassini/Huygens mission to Saturn and Titan. The mission is scheduled for November 2004. Huygens is an atmospheric probe designed to study the atmosphere and surface of Titan.
ABSTRACT: An assessment is made of the development status of concepts for cloud and aerosol compositions, vertical and horizontal distributions, and microphysical properties, in the Jovian upper troposphere and stratosphere. Attention is given to several key photochemical species' relationships to aerosol formation as well as their transport process implications, treating photochemistry in the context of comparative planetology and noting differences and similarities among the outer planet atmospheres; since this approach emphasizes observational data, a variegated assortment of ground-based and spacecraft observations is assembled. Current views on the tropospheric distribution of clouds are challenged, and a rationale is presented for alternative accounts.
ABSTRACT: The physical properties and spatial distribution of aerosol and cloud particles in Saturn's atmosphere are discussed based on data from remote measurement of scattered solar radiation and thermal radiation emitted from Saturn's atmosphere. A brief overview of the relations between particle properties and the scattered and emitted radiation field is given, and observations of Saturn at wavelengths from the ultraviolet to the thermal infrared which bear on the atmosphere's aerosol and cloud properties are reviewed. The single-scattering properties of the particles deduced from observations are discussed, commenting on the possible composition of the particles. The implications of the observations for the vertical and horizontal distribution of the clouds and aerosols are reviewed, and current information and areas for further research on the clouds and aerosols are summarized.
ABSTRACT: Spatially resolved measurements of Saturn's absolute reflectivity in methane bands at 6190, 7250, and 8900 A and in nearby continuum regions are presented. Images were obtained through narrow-band interference filters with a 500 x 500-pixel charge-coupled device. Band/continuum ratios were measured to high accuracy by referencing to the ring brightness in each image. Several data processing techniques enhanced the quality of the observations. These are the use of the ring symmetry to find center position and orientation, accurate subtraction of ring light, and constrained image deconvolution. Uncertainty in the continuum absolute reflectivity is within 10%. Uncertainties in band/continuum ratios are from one to several percent. The Equatorial Zone was much brighter than any other latitude in the strong 8900 band image. Northern midlatitudes were brighter than southern midlatitudes. The latter observation indicates fewer high-altitude aerosols in the south, a possible result of atmospheric dynamics or seasonal sublimation of NH3 crystals. The data are tabulated and presented in a form suitable for quantitative scattering model analyses.