Asteroid Mean Density Calculator

Mean density of an asteroid

Mean density comes out to ρ = M/V, where V = (4/3)π·r³ if the body is more or less spherical. The number tells you a lot about what the asteroid is made of. S-type asteroids (silicate, rocky) land around 2.5–3.5 g/cm³, M-type ones (metallic, iron-nickel) run 5–8 g/cm³, and C-type bodies (carbonaceous, primitive) sit at 1.3–2 g/cm³, frequently as porous rubble piles. Ceres makes a good example: with M ≈ 9.39·10²⁰ kg and r ≈ 470 km you get ρ ≈ 2.16 g/cm³, which fits a hydrated C-type carbonaceous body.

Applications

It shows up in Bus-DeMeo spectral classification, in working out whether asteroid mining is feasible (NASA's Psyche mission launched in 2023 toward a metallic M-type), in planetary defense with DART-style kinetic impactors where the momentum transfer hinges on porosity and density, and in pinning down how the early solar system came together.

FAQ

Why is the density of C-types so low? These aren't solid rock. They're loosely held rubble piles riddled with macro-porosity in the 30–50% range, so the bulk density ends up well under the grain density of the minerals inside them.

How is the mass M measured for an asteroid? A few ways: from the gravitational tug it puts on nearby bodies, from spacecraft tracking like OSIRIS-REx at Bennu or Hayabusa2 at Ryugu, or from the mutual orbits you see in binary systems.

And the volume V? That comes from radar imaging, light curves, occultations or shape models built directly by spacecraft. When the body is irregular you compute a polyhedral volume rather than leaning on (4/3)π·r³.