Washington, Mar 6 (ANI): Despite decades of Martian exploration, very little is known about Phobos, which is the larger and closer of the two natural satellites of Mars.
Many fundamental properties of this small potato-shaped body stay vague, for example, its gravitational field. SHI Xian and coauthors from Shanghai Astronomical Observatory and Technical University Berlin recently updated working models for the gravitational field of Phobos.
Mars has two natural satellites, Phobos and Deimos. Unlike the Earth's Moon, the Martian moons are relatively small in size and irregularly shaped.
Different scenarios have been suggested for the origin of these two bodies, such as captured asteroids or reaccreted ejectas from an impact event on Mars. However, none of the origin theories has yet been confirmed.
To unveil the mysteries of the Martian moons, scientists need more detailed understandings of their physical properties, among which the gravitational field is of great importance.
Existing gravitational field models of Phobos are all based on early shape models with relatively low resolution and precision. Since 2003, ESA's Mars Express (MEX) probe has been orbiting Mars in an elliptical polar orbit.
This special orbit allows it to perform regular flybys of Phobos, during which plenty of high-quality imaging data are accumulated. These data have helped establish a new, high-resolution shape model of Phobos. This provides a good opportunity to improve the gravitational field model.
The authors introduced three different methods to develop shaped-based gravitational field models, namely, the harmonic expansion approach (HEA), mass elements approach (MEA), and polyhedron approximation approach (PAA).
These methods are commonly used in gravitational field modelling for small solar system bodies. The HEA analytically transforms the spherical harmonic expansion coefficients of the shape model to the coefficients of the gravitational field model.
While treating the body as an accretion of cubes or a polyhedron, the MEA and PAA numerically calculate values of gravitational potential or force on a certain spatial grid.
All three methods have their own advantages, especially when considering different purposes.
Therefore, the authors adopted them all in the modelling. Comparisons of the results show good consistency, which further confirms the reliability of the acquired model as well as the feasibility of the methods.
Their study has been published in SCIENCE CHINA Physics, Mechanics 'n' Astronomy, 2012. (ANI)
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