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.
Their work, entitled "Working models for the gravitational field of Phobos", was published in SCIENCE CHINA Physics, Mechanics & Astronomy, 2012, Vol 55(2).
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 modeling 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 modeling. Comparisons of the results show good consistency, which further confirms the reliability of the acquired model as well as the feasibility of the methods.
A set of spherical harmonic coefficients for Phobos' gravitational field was obtained by applying the HEA. These coefficients complete a model up to degree and order 17, which is the most detailed one so far. Analyses of the lower-degree coefficients reflect characters of Phobos as an irregularly-shaped small body. The modeled value of is 20% less than the estimate reported by the MEX Radio Science team. However, since the estimate has an uncertainty of around 50%, this deviation indicates little about the internal structure of Phobos. These model coefficients are ready to be used as coarse or initial values in orbital analysis for spacecrafts. The HEA also yields a precise estimate of Phobos' volume as .
As deep space exploration goes on, more and more missions aim to land on small bodies like Phobos. Therefore, it has become necessary to model the surface gravity of these bodies. Due to the weak gravitation and relatively fast rotation, materials on the surface of these small bodies usually experiences a strange dynamical environment that is not always correlated to the topography. Using the MEA, the authors have produced a surface gravity map for Phobos. The gravity anomaly shows a large dynamic range of approximately . Prominent surface features such as crater Stickney can be identified easily.
The working models introduced in this article serve as a benchmark for further studies of Phobos' internal structure as well as surface environment. The authors are working on an in-depth comparative analysis between the dynamical environment and surface features, in search of hints about the surface evolutionary history of Phobos. Also, scientists can gain better insight into the internal mass distribution of Phobos when a more precise measurement is done for the gravitational field.
See the article: Shi X, Willner K, Oberst J, et al. Working models for the gravitational field of Phobos. Sci China-Phys Mech Astron, 2012, 55: 358-364, doi:10.1007/s11433-011-4606-4
Shi Xian | EurekAlert!
NASA Protects its super heroes from space weather
17.08.2017 | NASA/Johnson Space Center
New thruster design increases efficiency for future spaceflight
16.08.2017 | American Institute of Physics
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
17.08.2017 | Physics and Astronomy
17.08.2017 | Materials Sciences
17.08.2017 | Materials Sciences