What's a small fragments of matter (not asteroids) orbiting the sun?

Meteoroids

Explanation:

Meteoroids are small masses of rocks or metallic bodies that often found to orbit around the Sun. The size of a meteoroid is smaller in comparison to the asteroids. The elements that are found in the meteoroids are extraterrestrial nickel and iron. Meteoroids are often formed by the fragments from bodies present in universe such as Mars or Moon and thrown into space by an impact. After formation they often come in the range of attraction of Sun and start orbiting around it.

d.7.5cm is your answer

not too sure thinking all accelerations are pointed down