Relativity is a theory of gravity, and gravity governs the motion of planets. This is your answer in a nutshell. If you want a detailed answer, then I suggest you start studying general theory.
The planets orbit around the sun
1) The gravitational attraction between the planets and the Sun. 2) The "inertia" of the planets. That's their tendency to move in a straight line unless a force (gravity in this case) acts on them.
Planets orbit the sun in a counter clockwise motion, due to the balance between the Sun's gravity and the gravity of each individual planet.
The field of physics that studies the interactions between time and space is called spacetime physics or, more specifically, relativistic physics. This field encompasses Albert Einstein's theories of special relativity and general relativity, which describe the behavior of objects in relation to time, space, and gravity. It explores phenomena such as time dilation, length contraction, and the curvature of spacetime.
The motion of the planets are governed by a number of factors: Gravity - The planets are being pulled towards the Sun in free fall. The velocity of the planets - This balances against the force of gravity opposing it and producing on balance the orbit. The mass of the planets. The effect of gravitational attraction between the planet and any satellites it has. The effect of gravitational attraction between the planets and other planets/dwarf planets etc.
Yes. In the limit where the velocity difference between two observers gets ever closer to zero, the equations of spacial relativity reduce to the Newtonian equations. Indeed, if this were not true, then special relativity would be *wrong*. Similarly, general relativity gives the same answers as Newtonian gravity for the cases in which Newtonian gravity applies.
In between Mars and Venus
not particularly, essentially the effect of gravity depends on its mass and your distance from it
Gravity pulls in the sun and the planets to stay together in the orbit . The planets have gravitational force between them so they wont fall out.
Relativity has two parts: General relativity and special relativity, general relativity describes gravity as a geometric property of spacetime and special relativity is the physical theory of measurement in inertial frames of reference. Now quantum mechanics, in it's wave formulation, deals with describing things on the atomic scale as a wavefunction.
The forces of gravity between two masses are the cause of all orbits.
The force of attraction between heavenly bodies is called gravity. Usually, the solar system has the planets all kept in orbit by the gravity of the sun.