Planetary Collision Calculator    

This web tool calculates the outcome of collisions between gravity-dominated bodies and generates collision outcome maps. The scaling equations are appropriate for collisions onto planetary bodies larger than about 1 km. Other online tools calculate the outcomes for impact cratering events. The method is described in:

Leinhardt, Z. M., and S. T. Stewart. Collisions between Gravity-Dominated Bodies: 1. Outcome Regimes and Scaling Laws. Astrophysical Journal, 745, 79 (27pp), doi:10.1088/0004-637X/745/1/79, 2012. (PDF)

This page uses javascript and html5 to generate plots (RGraph compatible browsers).

Enter values for collision

Required parameters
    (assumed the same for both bodies)


    Material parameters: and (both are dimensionless)
        For fluid planets: c* = 1.9, μ = 0.35
        For solid planetesimals: c* = 5, μ = 0.37

Optional parameters needed to calculate a specific collision outcome
    Target radius (in km) =

    Impact velocity (in km/s) =

    Impact angle (0 to 90 degrees) =

Plot parameters
    Maximum value of Vimpact/Vesc on plot



The mutual escape velocity is Vesc = km/s.
For Vimpact/Vesc of and impact angle of degrees, the mass of the largest remnant is in units of Mtot.

The collision outcome regime is

On the plot, the collision is marked with an 'X'. Adjust the plot axis if necessary.

Save PNG [No canvas support]

The impact angle axis is scaled by probability such that the horizontal extent of each regime is proportional to the likelihood of that collision outcome. Mlr is the mass of the largest remnant after the collision; Mtot is the sum of the projectile and target mass; Vesc is the mutual escape velocity. Catastrophic disruption is defined as the specific energy needed to gravitationally disperse exactly half the total mass. Note that between perfect merging and hit-and-run, there is a graze-and-merge regime. Some perfect merging outcomes (e.g., for Mprojectile << Mtarget) include impact cratering events.

The 'Save PNG' button will generate an image from the html5 canvas plot.

Partial wish list: Add reverse impact calculation for erosion of projectiles in hit-and-run events; add optional graze-and-merge regime; add optional probability scaling for velocity axis.

Example Collision Outcomes

Merging of two water-rock planets (click on image for movie):

Catastrophic disruption of a water-rock planet:

Hit-and-run between two water-rock planets:

Animations are from calculations in Marcus et al. 2010.

Impact Cratering Calculators

Crater size and ejecta (Holsapple)
Crater size (Melosh)
Environmental effects and crater size (Marcus, Melosh, and Collins)

© Leinhardt & Stewart 2011
Please email problems/corrections to sstewart at
Updated December 12, 2011