= Safronov number
{c}
{title2=$\Theta$}
For a <planet> on a circular stellar <orbit>, a common convention is $\Theta=\tfrac12(v_{\rm esc}/v_k)^2$. The escape-to-orbital-speed ratio measures the size of a strong <gravitational assist> relative to the stellar binding <energy> of a nearby <comet>. Large values tend to favour ejection over collision; small values favour repeated weak encounters with more collision opportunities. This is a statistical comparison, dependent on the initial <orbit> and encounter geometry, rather than a universal outcome threshold.
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