According to the theory of relativity, an object moving at high speeds relative to an observer will experience length contraction in the direction of motion. This phenomenon is known as Lorentz contraction or relativistic contraction.
According to the Lorentz transformation equations, the length contraction factor (γ) is given by:
γ = 1 / √(1 - v^2/c^2)
where v is the velocity of the object and c is the speed of light.
As the velocity of the object approaches the speed of light, the value of γ becomes larger. This means that the length contraction effect becomes more significant as the object's speed increases.
If an object with an initial length D is moving at a velocity close to the speed of light relative to an observer, the observer will measure the length of the object to be contracted by a factor of γ. In other words, the measured length of the object in the direction of motion will be shorter than its rest length.
It is important to note that length contraction is a relative effect and depends on the observer's frame of reference. Different observers in different reference frames will measure different lengths due to the relativistic effects of time dilation and length contraction.
So, in the scenario you described, an object of length D moving towards Earth at a speed close to the speed of light will indeed appear contracted in length by a factor of γ when measured by an observer on Earth.