Planets are massive celestial bodies that orbit a star or stellar remnant. They are of many different sizes and compositions. Planets may have natural satellites (moons) and may or may not be inhabited. Every planet has a unique blurb, but most of them cannot be interacted with. Travel from planet to planet requires use of the Galaxy Map.
Within each solar system, there will usually only be one location to land / dock. Most often this will be a planet, but it may be a moon or starship instead. Many planets can be scanned from space for minerals or other collectibles, but not landed upon. There are even asteroids containing valuable metals or other objects hidden in the belts.
Mass Effect provides the radius of planets (in kilometers), and for planets with a solid surface it further provides the surface gravity (as a proportion of Earth's surface gravity). From these, it is possible to derive the mass (and density) for any planet with a surface gravity.
Isaac Newton'sgravitational constant is 6.67×10-11 m3kg-1s-2 which would be 6.67×10-20 km3kg-1s-2 when dimensioned for kilometers. Earth's surface gravity, g, is 9.81 ms-2, which is 9.81×10-3 kms-2. According to Newton's Law of Universal Gravitation, the mass of any body, M, is ar2G-1, where a is gravity, r the radius, and G the gravitational constant. Since the gravity of a planetary body in Mass Effect, s, is given as a proportion of Earth's, a = sg. Therefore, given values for s (dimensionless) and r (in km), and given that the mass of the Earth is 5.9736×1024 kg, the mass of a planet will be: