Journal
ASTRONOMY & ASTROPHYSICS
Volume 651, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/202038844
Keywords
gravitation; planets and satellites: formation
Categories
Funding
- pre-research Project on Civil Aerospace Technologies [D020103]
- National Natural Science Foundation of China [41804025, 42030110]
- DAR grant in planetology from the French Space Agency (CNES)
- Bundesministerium fur Wirtschaft and Energie, Berlin, via the German Space Agency DLR, Bonn
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The research indicates that Phobos may have a stratified internal structure with a core lighter than the mantle. However, the possibility of Phobos being homogeneous cannot be strictly ruled out.
Context. The origin of the Martian moons Phobos and Deimos is still poorly understood, and is the focus of intense debate.Aims. We demonstrate that a stratified internal structure of Phobos is compatible with the observed gravity coefficients.Methods. We fit previously derived C-20 and C-22 Phobos gravity coefficients derived from the combined MEX Doppler-tracking data from the close flybys in +2010 and 2013 with respect to the corresponding coefficients of a core-mantle stratification model of Phobos, with two opposite cases: a core denser than the mantle, and a core lighter than the mantle.Results. Only the case with a core lighter than the mantle fits at the 3 sigma level the previously reported observed second degree and order coefficient C-20, but a homogeneous Phobos cannot be strictly ruled out at the 3 sigma level.Conclusions. This possible loosening of the core density might be the result of a displacement of material toward the surface, may be caused by centrifugal forces acting on a loosely packed rubble-pile structure, and/or by a hot-then-cold in-orbit accretion process. These two hypotheses are by no means exhaustive.
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