Before 1950, the mass of Mercury was very poorly known, while the mass of Neptune, over one hundred times as far away, was known accurately. Mercury's orbit is highly elliptical. The rms velocity of O 2 in the earth's 300 K atmosphere is about 0.5 km sec. Pluto's orbit has an eccentricity of 0.249 .
Mean density is mass divided by volume.
The sun is going to turn into a red giant, with ten times its present radius and one half its present surface temperature. The luminosity of a star is proportional to the product of its surface area, which goes as the square of the radius, and the emission per unit surface area, which goes as the fourth power of temperature. You'll have the same temperature if you have the same flux hitting the earth. Flux is directly proportional to luminosity, and inversely proportional to the square of distance.