Planets move in elliptical orbits, not circles, so the concept of a diameter is not relevant.
The major axis of an ellipse is the distance along the line connecting the two most widely separated points on an ellipse and is roughly equivalent to the diameter of a circle. The major axis of the orbit of Mercury is about 0.774 Astronomical Units
23412846662834 Units
Mercury--0.387 astronomical units Venus--0.723 astronomical units Earth--1.0 astronomical units Mars--1.524 astronomical units Jupiter--5.203 astronomical units Saturn--9.529 astronomical units Uranus--19.19 astronomical units Neptune--30.06 astronomical units Pluto--39.53 astronomical units Please note that these are all mean distances, and the actual distance will vary as to the location of the specific planet in its specific orbit.
Mercury's orbit is the most elliptical of the eight planets' orbits, with eccentricity of 0.206. Mercury has an average distance from the Sun of 0.387 astronomical units, and the Sun is off-centre by 20.6% of that, or 0.080 astronomical units. So Mercury's distance varies from 0.307 to 0.467 AU, or in kilometres 46 millon to 70 million, which is quite strange. The Sun's rays that shine on Mercury are more than twice as intense at the closest approach as they are at the furthest away.
Mercury has the smallest orbit, and Neptune has the largest orbit in our solar system. This is determined by the average distance of each planet from the Sun. Mercury's average distance is about 0.39 astronomical units (AU), while Neptune's average distance is about 30.07 AU.
Oh, an interesting question! Mercury's semimajor axis - which is the distance from the center of the Sun to the farthest point of Mercury's orbit - is about 0.39 astronomical units, or around 57.9 million kilometers. That's a nice and cozy space for our little Mercury to dance gracefully around the warm Sun. Nature has a way of creating beauty in all the details like this, doesn't it?
0.387 is the average distance from the Sun to Mercury in AU. Note: AU=astronomical unit
The diameter of Earth is approximately 12,742 kilometers. In astronomical units (AU), where 1 AU is the average distance from the Earth to the Sun (about 149.6 million kilometers), Earth's diameter is about 0.000085 AU. This illustrates how small Earth is compared to the vast distances in space.
The orbit of Mercury is elliptical. This means that its orbit travels the path of an ellipse, and isn't always the same distance from the Sun. When Mercury makes its closest approach to the Sun, astronomers call this perihelion. So, the perihelion of Mercury is 46 million kilometers (29 million miles), or 0.307 astronomical units (1 AU is the distance from the Sun to the Earth). The furthest point of a planet's orbit is called the aphelion. So in the case of Mercury, its furthest point stretches out to 70 million km (44 million miles), or 0.466 astronomical units.
Eris is 97 astronomical units away from the sun. ( an astronomical unit is the average distance between Earth and the Sun)
Same as Jupiter, since Callisto is a moon of Jupiter.
70 million km (44 million miles), or 0.466 astronomical units
Mercury from the sun 57,910,000 km (0.38 astronomical units), closest to the sun.