Low-degree gravity field recovery of Phobos based on MEX flyby data

The accurate Phobos gravity field model can provide informative constraints for modeling internal structure of Phobos. An in-depth understanding of the internal structure of Phobos will provide an important basis on interpreting origin and evolution for Martian system and even the evolution of the solar system. However, the Phobos gravity field model has not been accurately determined. In order to obtain the Phobos low-degree gravity field model, the radio tracking data of Mars Express during Phobos flyby in 2010 and 2013 were processed. Through the modeling of various high-fidelity force models of the spacecraft and combined the two flyby data, the resulting Phobos GM is (7.0768 ±0.0084)×10 5  m 3 /s 2 , the C 20 value −0.1370±0.0392, and the C 22 value 0.0184±0.0174. The solution coincided with the results released by the Mars radio science team, and the precision increased by two to three times. According to the GM we obtained, the mass of Phobos could be estimated at (1.060 ±0.0011)×10 16  kg, and with the volume of Phobos (5742±35) km 3 , the Phobos bulk density is (1847±11) kg/m 3 .