Phobos: Observed bulk properties

Pätzold, M.; Andert, T. P.; Jacobson, R. A.; Rosenblatt, P.; Déhant, V.

doi:10.1016/j.pss.2014.01.004

Cited by 35 publications

(23 citation statements)

References 21 publications

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“…To date, such gravity field models are available for only a limited number of solar system bodies. For Phobos, results from radio science data reduction merely show signals for low degree terms of its gravity field due to the short-arc data from flyby and an unfavorable observation geometry (Andert et al, 2011;Pätzold et al, 2014). Therefore, it is appropriate and practical to develop working models for the gravity field of Phobos using shape-based forward modeling method.…”

Section: Methodsmentioning

confidence: 99%

Phobos' shape and topography models

Willner

Shi

Oberst

2014

Planetary and Space Science

104

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The global shape and the dynamic environment are fundamental properties of a body. Other properties such as volume, bulk density, and models for the dynamic environment can subsequently be computed based on such models. Stereo-photogrammetric methods were applied to derive a global digital terrain model (DTM) with 100 m/pixel resolution using High Resolution Stereo Camera images of the Mars Express mission and Viking Orbiter images. In a subsequent least-squares fit, coefficients of the spherical harmonic function to degree and order 45 are computed. The dynamic models for Phobos were derived from a polyhedron representation of the DTM. The DTM, spherical harmonic function model, and dynamic models, have been refined and represent Phobos' dynamic and geometric topography with much more detail when compared to Shi et al. (2012) and Willner et al. (2010) models, respectively. The volume of Phobos has been re-determined to be in the order of 5741 km 3 with an uncertainty of only 0.6% of the total volume. This reduces the bulk density to 1.867 0.013 g/cm 3 in comparison to previous results. Assuming a homogeneous mass distribution a forced libration amplitude for Phobos of 1.141 is computed that is in better agreement with observations by Willner et al. (2010) than previous estimates.

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Section: Methodsmentioning

confidence: 99%

Phobos' shape and topography models

Willner

Shi

Oberst

2014

Planetary and Space Science

104

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“…As a result, some of our calculations above, which utilise perfect merging upon collision, are probably naive. On the other hand, the low densities of Phobos and Deimos (Andert et al 2010;Pätzold et al 2014) are often used as arguments to suggest that they are rubble piles, likely substantially fractured during prior evolutionary stages. This is eminently consistent with the energetics of the above scenarios.…”

Section: Discussionmentioning

confidence: 99%

A dynamical context for the origin of Phobos and Deimos

Hansen

2018

Monthly Notices of the Royal Astronomical Society

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We show that a model in which Mars grows near Earth and Venus but is then scattered out of the terrestrial region yields a natural pathway to explain the low masses of the Martian moons Phobos & Deimos. In this scenario, the last giant impact experienced by Mars is followed by an extended period (tens to hundreds of Myr) of close passages by other planetary embryos. These close passages perturb and dynamically heat any system of forming satellites left over by the giant impact and can substantially reduce the mass in the satellite system (sometimes to zero). The close passage of massive perturbing bodies also offers the opportunity to capture small objects by three-body scattering. Both mechanisms lead to low mass moon systems with a substantially collisional history.

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“…The knowledge of the gravity field when combined with other bulk parameters, such as shape, volume, bulk density, porosity, and water ice content are key information for models of internal mass distribution, structure, composition, and Deimos/Phobos origins. Using data from X-band radio tracking during recent spacecraft flybys, especially by Mars Express (Andert et al, 2010;Pätzold et al, 2014b;Rosenblatt et al, 2008), the mass of Phobos has been estimated as 1.065 ± 0.016 10 16 kg (Pätzold et al, 2014a). The higher degree and order terms of the gravity fields (e.g., the C 20 and the C 22 terms) of Phobos suffer from large uncertainties (Pätzold et al, 2014b), due to the faint gravity signatures, the high spacecraft flyby speeds and the large flyby distances.…”

Section: Mass and Gravity Fieldmentioning

confidence: 99%

“…Detection of ice repositories would provide a strong constraint on the moons origins. However, neither the proportions of rock and water nor the origin of Deimos and Phobos can be constrained by the bulk density alone (Pätzold et al, 2014a;Rosenblatt, 2011).…”

Section: Interior Modelsmentioning

confidence: 99%

“…The attracting forces of the small moons and other non-gravitational forces act on the spacecraft and change its trajectory and speed, which can be precisely extracted from the Doppler shift of the radio carrier frequency received on ground (for details see: Andert et al, 2010;Pätzold et al, 2011;Pätzold et al, 2014a;2014b;). The mass and gravity field of the body when combined with the body´s volume and shape determined from camera observation, pose constraints on the bulk density and hint at the internal structure and composition and porosity considerations, as demonstrated during the Mars Express flybys of Phobos (Andert et al, 2010;Pätzold et al, 2014a;2014b) and the Rosetta flyby at asteroid 21 Lutetia (Pätzold et al, 2011).…”

Section: Gravity Radio Science Investigation Of the Martian Moons -Grimmmentioning

confidence: 99%

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DePhine – The Deimos and Phobos Interior Explorer

Oberst

Wickhusen

Willner

et al. 2018

Advances in Space Research

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DePhine -Deimos and Phobos Interior Explorer -is a mission proposed in the context of ESA's Cosmic Vision program, for launch in 2030. The mission will explore the origin and the evolution of the two Martian satellites, by focusing on their interior structures and diversity, by addressing the following open questions: Are Phobos and Deimos true siblings, originating from the same source and sharing the same formation scenario? Are the satellites rubble piles or solid bodies? Do they possess hidden deposits of water ice in their interiors? The DePhine spacecraft will be inserted into Mars transfer and will initially enter a Deimos quasi-satellite orbit to carry out a comprehensive global mapping. The goal is to obtain physical parameters and remote sensing data for Deimos comparable to data expected to be available for Phobos at the time of the DePhine mission for comparative studies. As a highlight of the mission, close flybys will be performed at low velocities, which will increase data integration times, enhance the signal strength and data resolution. 10 -20 flyby sequences, including polar passes, will result in a dense global grid of observation tracks. The spacecraft orbit will then be changed into a Phobos resonance orbit to carry out multiple close flybys and to perform similar remote sensing as for Deimos. The spacecraft will carry a suite of remote sensing instruments, including a camera system, a radio science experiment, a high-frequency radar, a magnetometer, and a Gamma Ray / Neutron Detector. A steerable antenna will allow simultaneous radio tracking and remote sensing observations (which is technically not possible for Mars Express). Additional instrumentation, e.g. a dust detector and a solar wind sensor, will address ---further science goals of the mission. If Ariane 6-2 and higher lift performance are available for launch (the baseline mission assumes a launch on a Soyuz Fregat), we expect to have greater spacecraft mobility and possibly added payloads.

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Phobos: Observed bulk properties

Cited by 35 publications

References 21 publications

Phobos' shape and topography models

Phobos' shape and topography models

A dynamical context for the origin of Phobos and Deimos

DePhine – The Deimos and Phobos Interior Explorer

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