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Publications (120)
The JUpiter ICy moons Explorer (JUICE) of ESA was launched on 14 April 2023 and will arrive at Jupiter and its moons in July 2031. In this review article, we describe how JUICE will investigate the interior of the three icy Galilean moons, Ganymede, Callisto and Europa, during its Jupiter orbital tour and the final orbital phase around Ganymede. De...
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Mineral assemblages that constitute the mantles of reduced exoplanets, such as those formed in the inner regions of stellar nebulae, have been scarcely investigated. We propose that these exoplanets share several physical and chemical properties with planet Mercury in our Solar System, as they formed in a similar geochemical...
The surface of Venus has undergone substantial alterations due to volcanic activity throughout its geological history, and some volcanic features suggest that this activity persisted until as recently as 2.5 million years ago. Recent evidence of changes in the surface morphology of a volcanic vent has been interpreted as a potential indication of o...
This Research Briefing, associated with the article "Evidence of ongoing volcanic activity on Venus revealed by Magellan radar," (DOI: 10.1038/s41550-024-02272-1) provides a simplified explanation of our research findings, making them accessible to a wider audience.
Radar signals of the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument at the base of the South Polar Layered Deposits (SPLD) in the region known as in Ultimi Scopuli, Mars, have been interpreted as reflections from putative subglacial standing bodies of liquid water. The interpretation of the MARSIS radar signals is no...
Ganymede will be the first icy satellite in the Solar System orbited by a spacecraft, ESA’s JUpiter ICy moons Explorer (JUICE). JUICE launch is scheduled for April 2023 and the arrival at Ganymede is foreseen in 2035.
Thanks to the advanced Ka-band radio tracking system, the Geodesy and Geophysics of Jupiter and Galilean Moons (3GM) experiment aboa...
The surface morphology of Triton is believed to be predominantly influenced by endogenic processes, such as tectonism, volcanism, diapirism and geyser-like eruptions. To understand how some of these processes have reshaped the surface of the satellite during its evolutionary history, we performed a geological analysis of an extended area located in...
A new solution of Mercury's gravity field to degree and order 160, named HgM009, is retrieved through a reprocessing of MESSENGER radio science measurements. By combining our latest gravity field with topography data, localized spectral admittance analyses are carried out to investigate Mercury's crustal and lithospheric properties across the north...
Triton, the largest satellite of Neptune, is one of the most fascinating icy moons in the outer Solar System, with an origin that likely extends to the Kuiper Belt. Like other icy satellites, the mineralogical composition of Triton's deep interior is a function of its evolutionary path. In this work, we use the open- access Perple_X software to mod...
Enceladus is the first planetary object for which direct sampling of a subsurface water reservoir, likely habitable, has been performed. Over a decade of flybys and seven flythroughs of its watery plume, the Cassini spacecraft determined that Enceladus possesses all the ingredients for life. The existence of active eruptions blasting fresh water in...
We present a White Paper with a science theme concept of ocean world evolution and habitability proposed in response to ESA’s Voyage 2050 Call with a focus on Titan and Enceladus in the Saturn system. Ocean worlds in the outer Solar System that possess subsurface liquid water oceans are considered to be prime targets for extra-terrestrial life and...
Monitoring of vibrational eigenmodes of an elastic body excited by gravitational waves was one of the first concepts proposed for the detection of gravitational waves. At laboratory scale, these experiments became known as resonant bar detectors first developed by Joseph Weber in the 1960s. Due to the dimensions of these bars, the targeted signal f...
The Mercury Orbiter Radio Science Experiment (MORE) of the ESA mission BepiColombo will provide an accurate estimation of Mercury’s gravity field and rotational state, improved tests of general relativity, and a novel deep space navigation system. The key experimental setup entails a highly stable, multi-frequency radio link in X and Ka band, enabl...
Evidence for tectonic activity on Titan is provided by the presence of eroded mountain ranges. Xanadu is an equatorial region of Titan characterized by a complex topography, even though, overall, it has a lower average elevation compared to its surroundings. We investigated Xanadu's southwestern margin, a part of the region composed of heavily erod...
Monitoring of vibrational eigenmodes of an elastic body excited by gravitational waves was one of the first concepts proposed for the detection of gravitational waves. At laboratory scale, these experiments became known as resonant-bar detectors first developed by Joseph Weber in the 1960s. Due to the dimensions of these bars, the targeted signal f...
The Geodesy and Geophysics of Jupiter and the Galilean Moons (3GM) experiment aboard the JUpiter ICy moons Explorer (JUICE) will measure the gravity fields of Europa, Callisto and Ganymede. For the first two moons the data will be acquired during flybys, while for Ganymede a 9-months orbital phase is planned. This latter phase is divided in a 5-mon...
The gravity and shape data acquired by the Dawn spacecraft during its primary mission revealed that Ceres is partially differentiated with an interior structure consistent with a volatile-rich crust, a mantle of hydrated rock and isostatically compensated topography1,2,3. Detailed analyses showed that the mechanically strong crust overlays a weak,...
Evidence for tectonic activity on Titan is provided by the presence of eroded mountain ranges. Xanadu is an equatorial region of Titan characterized by a complex topography, even though overall it has a lower average elevation compared to its surroundings. We investigated Xanadu’s southwestern margin, a part of the region which is comprised of heav...
A growing number of satellites in the outer solar system likely have global oceans beneath their outer icy shells. While the presence of liquid water makes these ocean worlds compelling astrobiological targets, the exchange of heat and materials between the deep interior and the surface also plays a critical role in promoting habitable environments...
The aim of this chapter is to describe available evidence for the existence of relict ocean worlds. The focus is on Ceres as a clear example of such a world as indicated by the results from the Dawn mission. The sections of this chapter will also reflect the differences and commonalities with other recognized ocean worlds. We focus on Ceres as an e...
The presence of liquid water at the base of the Martian polar caps has long been suspected but not observed. We surveyed the Planum Australe region using the Mars Advanced Radar for Subsurface and Ionosphere Sounding, a low-frequency radar on the Mars Express spacecraft. Radar profiles collected between May 2012 and December 2015, contain evidence...
The Cassini mission discovered lakes and seas comprising mostly methane in the polar regions of Titan. Lakes of liquid nitrogen may have existed during the epochs of Titan’s past in which methane was photochemically depleted, leaving a nearly pure molecular nitrogen atmosphere and, thus, far colder temperatures. The modern-day small lake basins wit...
Evidence for tectonic activity on Titan is exemplified by the presence of eroded mountain ranges [5,7], although it is unclear whether their origin is endoge-nic [6]. Xanadu is Titan's largest surface feature, possesses the highest albedo and has an average elevation ranging between-200 to 200 meters. It has been proposed that Xanadu has had a comp...
Global maps of Titan show great diversity in terrain types, but their associations with specific compositions on a large scale are obscured by Titan’s thick atmosphere, which shrouds the weak spectral features. Here we develop a principal component analysis (PCA) that enables the identification of subtle spectral features. The PCA was applied to ov...
In the version of this Article originally published, the author Rosaly Lopes was mistakenly affiliated with Northern Arizona University. Her affiliation has now been corrected to: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
Saturn’s largest moon, Titan, hosts liquid hydrocarbon lakes and seas on its surface. During the last close encounter with Titan (22 April 2017), the Cassini spacecraft used its RADAR as a sounder to probe the depth of several lakes in the north polar terrain. This was the first time that Titan’s lakes, as opposed to its seas, have been viewed in a...
Titan was a mostly unknown world prior to the Cassini spacecraft’s arrival in July 2004. We review the major scientific advances made by Cassini’s Titan Radar Mapper (RADAR) during 13 years of Cassini’s exploration of Saturn and its moons. RADAR measurements revealed Titan’s surface geology, observed lakes and seas of mostly liquid methane in the p...
Evidence for tectonic activity on Titan is exemplified by the presence of eroded mountain ranges (Radebaugh et al., 2007; Mitri et al., 2010), although it is unclear whether their origin is endogenic (Moore and Pappalardo, 2011). Due to low SAR resolution and paucity of elevation data, tectonic indicators on Titan are often best identified by indir...
Liquid water under Mars' southern ice cap
Mars is known to host large quantities of water in solid or gaseous form, and surface rocks show clear evidence that there was liquid water on the planet in the distant past. Whether any liquid water remains on Mars today has long been debated. Orosei et al. used radar measurements from the Mars Express spa...
Titan, with its organically rich and dynamic atmosphere and geology, and Enceladus, with its active plume, both harbouring global subsurface oceans, are prime environments in which to investigate the habitability of ocean worlds and the conditions for the emergence of life. We present a space mission concept, the Explorer of Enceladus and Titan (E²...
Ganymede shows an icy crust strongly shaped by past and possibly still active tectonics. Kilometric morphotectonic features, grooves and furrows, develop within the light terrain and the dark terrain, respectively. Open debate exist on the geodynamic processes responsible for these features. In this contribution we explore the tectonic setting of t...
Five decades of observations of Ceres suggest that the dwarf planet has a composition similar to carbonaceous meteorites and may have an ice-rich outer shell protected by a silicate layer. NASA’s Dawn spacecraft has detected ubiquitous clays, carbonates and other products of aqueous alteration across the surface of Ceres, but surprisingly it has di...
The formation of Ganymede's sulci is likely related to extensional tectonics that affected this largest icy satellite of Jupiter. Through geometric and structural analyses we reconstructed the pre-deformed terrains and we recognized two different modes of extension associated with sulci. In the first mode, smooth sulci constitute spreading centers...
Ganymede, the largest satellite of Jupiter, shows an icy crust strongly shaped by past and possibly still active tectonics. The surface is subdivided into two terrains, i.e. dark and light terrains, and morphotectonic features are present in both of them. The younger light terrains represent about 65% of the surface and show the presence of deforma...
The intense plume activity at the South Pole of Enceladus together with the recent detection of libration hints at an internal water ocean underneath the outer ice shell. However, the interpretation of gravity, shape, and libration data leads to contradicting results regarding the depth of ocean/ice interface and the total volume of the ocean. Here...
We propose a strategy to evaluate the performance of a radar sounder for the subsurface exploration of the Europa icy crust and, in particular, the possibility to detect liquid water at the base of the ice shell. The approach integrates the information coming from experimental measurements of the dielectric properties of icy materials, thermal mode...
Between 2004 and 2009 the RADAR instrument of the Cassini mission provided 31 SAR images of Titan. We tracked the position of 160 surface landmarks as a function of time in order to monitor the rotational dynamics of Titan. We generated and processed RADAR observables using a least squares fit to determine the updated values of the rotational param...
Since the late 1970’s, the possibility of ice on Ceres has been a topic of broad discussion that engages data ranging from surface spectroscopy to shape and density. Thermal models suggest that subsurface ice on Ceres is stable for the lifetime of the solar system. Dawn arrived at Ceres in 2015 with a suite of instruments to answer this question bu...
In order to support the JUICE mission and in particular RIME activities, we have initiated a research effort for understanding the geology of Ganymede.
Introduction: Icy moons of Jupiter have regained attention recently with the approval of the JUpiter ICy moons Explorer (JUICE) mission by the European Space Agency and its partners for a scheduled launch in 2022 and arrival in the Jovian system in 2030. The instruments particularly important and relevant to geological investigation of the icy moon...
Saturn's moons, Titan and Enceladus, are two of the Solar System's most enigmatic bodies and are prime targets for future space exploration. Titan provides an analogue for many processes relevant to the Earth, more generally to outer Solar System bodies, and a growing host of newly discovered icy exoplanets. Processes represented include atmospheri...
Fundamental questions involving the origin, evolution, and history of both Titan and the broader Saturnian system can be answered by exploring this satellite from an orbiter and also in situ. We present the science case for an exploration of Titan and one of its lakes from a dedicated orbiter and a lake probe. Observations from an orbit-platform ca...
JANUS (Jovis, Amorum ac Natorum Undique Scrutator) is the visible camera selected for the ESA JUICE mission to the Jupiter system. Resources constraints, S/C characteristics, mission design, environment and the great variability of observing conditions for several targets put stringent constraints on instrument architecture. In addition to the usua...
[1] We construct the depth profile—the bathymetry—of Titan's large sea Ligeia Mare, from Cassini RADAR data collected during the 23 May 2013 (T91) nadir-looking altimetry fly-by. We find the greatest depth to be about 160 m and a seabed slope that is gentler towards the northern shore, consistent with previously imaged shoreline morphologies. Low r...
Based on recent results on the tidal deformation and obliquity of Titan, we will predict tidal and rotational signatures of an internal ocean inside Ganymede and Callisto to be tested by the future ESA’s JUICE mission.
This paper presents the Radar for Icy Moons Exploration (RIME) instrument, which has been selected as payload for the JUpiter Icy moons Explorer (JUICE) mission. JUICE is the first Large-class mission chosen as part of the ESA's Cosmic Vision 2015-2025 programme, and is aimed to study Jupiter and to investigate the potentially habitable zones in th...
Based on comprehensive mapping of the region, the recent theories of Xanadu’s origin are examined and a chronology of geologic processes is proposed. The geologic history of Titan’s Xanadu region is different from that of the other surface units on Saturn’s moon. A previously proposed origin of western Xanadu from a giant impact in the early histor...
Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) is
an orbital subsurface sounder aboard ESA's Mars Express spacecraft . It
transmits a low-frequency radar pulse that is capable of penetrating
below the surface, and is reflected by subsurface dielectric
discontinuities. MARSIS has been used to probe both the south and the
north...
Titan's Xanadu region reveals a multitude of geologic features such as
fluvial channels, mountains, and lake-like features; the confluence of
all these makes Xanadu special. Nevertheless, the geologic history and
interplay of geologic processes remains largely unexplained. Recent
studies conclude the region as a whole is ancient (e.g. Wood et al.
2...
MARSIS subsurface radar sounder data from 2011 allowed us to start to map in three deminsions the internal structure of the North Pole of Mars, and in particular we are exploring the structure of the Basal Unit.
Titan's Xanadu region is one of the most fascinating, continent-sized
surface features, hosting many kinds of geologic features, such as
craters, channels, candidate paleolakes, mountain chains, and potential
cryovolcanic flows. However, the geologic development of this region is
still controversially debated. This study aims to verify current
conc...
Cassini RADAR images of Titan’s south polar region acquired during southern summer contain lake features which disappear between observations. These features show a tenfold increases in backscatter cross-section between images acquired one year apart, which is inconsistent with common scattering models without invoking temporal variability. The mor...
Titan’s enigmatic Xanadu province has been seen in some detail with instruments from the Cassini spacecraft. The region contains some of the most rugged, mountainous terrain on Titan, with relief over 2000 m. Xanadu contains evolved and integrated river channels, impact craters, and dry basins filled with smooth, radar-dark material, perhaps sedime...
1] We have developed a thermal model of Titan's interior to study changes in volume during partial freezing or melting of a subsurface ocean due to heat flux variations from the interior. We find that the long‐term cooling of Titan can cause global volume contraction DV/V ∼0.01. We then simulate two‐dimensional contractional deformation of Titan's...
The discovery of numerous extra-terrestrial volcanoes, including active ones, has stretched our traditional definition of what a volcano is. We now know that the nature of volcanism is highly variable over the solar system, and the traditional definition of a volcano as defined for Earth needs to be modified and expanded to include processes such a...
Ontario Lacus' shoreline features include Earth-like rivers, deltas and flooded topography. Ontario is a dynamic lake, similar in many ways to terrestrial lakes, with active shoreline processes.
Of more than 400 filled lakes now identified on Titan, the first and largest reported in the southern latitudes is Ontario Lacus, which is dark in both infrared and microwave. Here we describe recent observations including synthetic aperture radar (SAR) images by Cassini's radar instrument (λ = 2 cm) and show morphological evidence for active mater...
We model the accretion, evolution and interior structure of Titan, using
the gravity data as constraints.
The Cassini Titan Radar Mapper is providing an unprecedented view of Titan’s surface geology. Here we use Synthetic Aperture Radar (SAR) image swaths (Ta–T30) obtained from October 2004 to December 2007 to infer the geologic processes that have shaped Titan’s surface. These SAR swaths cover about 20% of the surface, at a spatial resolution ranging...
The goal of this chapter is to give a description of Titan's interior that is consistent with the new constraints provided by the Cassini mission. As the Cassini mission proceeds into its first extended phase, the data obtained during the nominal mission suggest that Titan is at least partially differentiated. An ocean would be present some tens of...
Ephemeral hydrocarbon liquids have been observed in Titan's south polar
region by the Cassini RADAR during southern summer. A collection of
features, whose morphologies match that of previously identified
partially-filled lakes, show more than an order of magnitude increase in
backscatter. The morphologic boundaries of these features are transient...
The discovery of numerous extra-terrestrial volcanoes, including active ones, has stretched our traditional definition of what is a volcano. We now know that the nature of volcanism is highly variable over the Solar System, and the traditional definition of a volcano as defined for Earth needs to be modified and expanded to include processes such a...
The recent measurement of the gravity coefficients from the Radio
Doppler data of the Cassini spacecraft has improved our knowledge of the
interior structure of Titan (Rappaport et al. 2008 AGU, P21A-1343). The
measured gravity field of Titan is dominated by near hydrostatic
quadrupole components. We have used the measured gravitational
coefficient...