Unsolved mysteries about the solar system

We don't know many things about our solar system.  Such unsolved mysteries are   - - -

1.  Origin of water on Earth 

                Origin of water on Earth is still a mystery. We don't know whether it originated from comets or asteroids or was already present within Earth during its formation.

2.  Origin of moon 

                 Formation of the moon is still contentious one.  Some suggest massive Earth and Mars collision. Some suggest earth's gravity or simultaneous formation alongside Earth.

3.  Magnetic fields of outer planets

                    Planets like Jupiter, Saturn, Uranus and Neptune have very strong magnetic field. But their exact mechanism and dynamics are still not known.

4..  Tilt of Uranus axis

                98 degree axial tilt of Uranus is still a mystery.  It may be attributed to the collision or the gravitational pull of nearby planets.

5.  Origin of Saturn 's rings

                     It may be from the remnants of a moon shattered by the tidal pressure or debris from the comet encounters.  Reason is still unclear.

6.  Unsolved mysterious features on Mars

                        Mars has seasonal violations, methane spikes and recurrent slope lines which may be the sign of liquid water..

7.  Kuiper Belt objects and their composition

                    Objects in Kuiper Belt like Pluto and other dwarf planets have varied composition which is still not known.