"Ever the since their discovery in 1877 by American astronomer Asaph Hall, the two moons of Mars, Phobos and Deimos, have been mysteries. Spacecraft missions have revealed that they are irregular-shaped small bodies with a long collisional history and complex geology, but their origin remains unknown. Three very different hypotheses have been proposed for their origin: 1) They are captured asteroids, possibly primitive D-type asteroids from the outer part of the main asteroid belt; 2) They are remnants of Mars’s own formation; 3) They are reaccreted impact ejecta from Mars. Superimposed on these hypotheses is another unresolved hypothesis: 4) Phobos and Deimos were once part of a single larger object.
There are also two intriguing hypotheses concerning the present evolution of Phobos and Deimos: 5) A faint dust cloud fed by micrometeoroid impacts exists in steady-state in the immediate vicinity of Phobos and Deimos; 6) A faint dust ring and a faint dust torus occur at the location of Phobos and Deimos’s orbits, respectively.
Each one of these hypotheses has radically different implications regarding the evolution of the solar system, and/or the origin and evolution of its planets, satellites, and/or rings. These hypotheses are best tested or at least constrained by simultaneously investigating the internal structure and bulk composition of Phobos and Deimos, and the abundance and distribution of dust in their vicinity.
The Phobos And Deimos & Mars Environment (PADME) mission is a proposed new NASA Discovery mission that would test the above hypotheses by investigating simultaneously the internal structure and bulk composition of Phobos and Deimos, and the abundance and distribution of dust in Mars orbit.
The PADME mission would use the proven LADEE spacecraft bus, radio science, and a suite of highly mature instruments to achieve its science objectives. PADME would launch in 2020 and reach Mars orbit in early 2021. It would then begin a series of slow and increasingly close flybys of Phobos to carry out the following baseline observations in unprecedented detail: a) measure the small body’s gravity field, b) image its position, orientation, shape, and surface features; c) measure the bulk composition of the regolith; d) measure the abundance and distribution of dust in its vicinity. The same series of observations would then be performed at Deimos.
PADME would offer a low-cost and low risk giant leap in our knowledge about the evolution of the solar system and the origin and evolution of small bodies, of small planetary satellites, of planetary rings, and of Phobos and Deimos specifically. PADME would also fill key strategic knowledge gaps identified by NASA’s HEOMD in advance of planning human missions to Phobos and/or Deimos. PADME would be built, managed, and operated by NASA Ames Research Center. Partners include the SETI Institute, NASA JPL, NASA KSC, University of Colorado, University of Maryland, Cornell University, Royal Observatory of Belgium, JAXA, and others."