Phobos' shape and topography models

Abstract

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.

CassiniISS astrometry of the Saturnian satellites: Tethys, Dione, Rhea, Iapetus, and Phoebe 2004–2012

“…In addition, fitting an ellipsoid to such an irregular shape does not provide the best astrometry. The best solution would be to build a 3D model of Phoebe based on a high order of spherical harmonics expansion similar to the work done on Phobos (Willner et al 2014). Phoebe was only observed in high resolution during the seven days of the Cassini flyby in June 2004 immediately before orbit insertion.…”

Planetary Cartography and Mapping: Where We Are Today, and Where We Are Heading For?

“…Thus, the USGS ACS established cooperation with institutions like NASA (at multiple programmatic levels), European Space Agency (ESA), and Jet Propulsion Laboratory (JPL) but also community organizations such as the International Astronomical Union (IAU) (Shingareva et al, 2005). Intense international collaborations in the course of ESA's Mars Express have resulted in Phobos special issue (Oberst et al, 2014) and The Phobos Altas (Savinykh et al, 2015). Nowadays, the MIIGAiK Extraterrestrial Laboratory (MExLab) is focusing on planetary geodesy and GIS-based cartography methods for Solar System bodies (Karachevtseva et al, 2016;Shevchenko, 2016).…”

“…A new set of cartographic products based on the integration of data from multiple orbits was produced and published recently (Gwinner, et al, 2016). Controlled images and ortho-image mosaics were also produced and published for Phobos (Wä hlisch et al, 2010(Wä hlisch et al, , 2014Willner et al, 2010Willner et al, , 2014, or the Icy Saturnian Satellites (4) (Roatsch et al, 2009). For Ceres and Vesta, global mosaics serve as base map for different atlas collections (5) (e.g.…”

Astrometric observations of Phobos with the SRC on Mars Express

“…Images taken during these close approaches have been used to create a control-point network , a 3D shape model (Willner et al , 2014, and a topographic image atlas (Wählisch et al 2010(Wählisch et al , 2014. The control-point network and the 3D shape model were used for the astrometric measurement methods applied in this paper.…”

“…While the former is based on Phobos' control-point network, the latter is founded on Phobos' gridded shape model. In the implementation of these methods we used the latest versions of both models by Willner et al (2010Willner et al ( , 2014. The coordinates of control points are believed to be given with respect to the Phobos center of mass (COM) as defined by the MAR080 ephemeris.…”