Astronomy & Space
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Hill Sphere Radius

The zone where a body's gravity dominates over its host's.

Formula

rH≈a(m3M)1/3r_H \approx a\left(\frac{m}{3M}\right)^{1/3}

Variables

aOrbital radius
mBody mass
MHost mass

Example

Earth's Hill sphere reaches about 1.5 million km

Did You Know?

A moon can only orbit stably well inside its planet's Hill sphere — the Moon sits comfortably within Earth's.

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