Computes the close-approach geometry for the 2029-04-13 flyby of asteroid 99942 Apophis. At the nominal JPL perigee of 38,017 km from Earth's centre — well inside geostationary orbit at 42,164 km — this is the closest-ever observed approach of a large asteroid. Calculates tidal acceleration across the body and perigee speed from the vis-viva equation.
Confirmed upcoming event — 2029-04-13
Apophis will pass at ~38,017 km from Earth's centre (JPL/CNEOS solution #197). Two spacecraft are en route: NASA OSIRIS-APEX (arriving 2029-04-13) and ESA Ramses (launch target Apr 2028). All JPL orbital solutions since 2021 rule out Earth impact in 2029.
Close-approach parameters
38,017 km
Earth-centre distance at closest approach. JPL nominal: 38,017 km. GEO at 42,164 km.
340 m
Mean diameter. Radar shape model: ~340 m ± ~30 m (Brozovic et al. 2018).
7.43 km/s
Hyperbolic excess velocity (v_inf). Used in vis-viva: v_peri² = v_inf² + 2·GM/r.
Results
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tidal dg (m/s² across body)
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v_perigee (km/s)
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speed boost vs. v_inf (km/s)
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GEO crossing status
Building artifact...
What this tool computes
Tidal acceleration across the asteroid body (classical tidal formula):
dg = 2 · GM_earth · d / r³
where d is the asteroid diameter (m), r is the perigee distance (m). Units: m/s².
Perigee speed from the vis-viva equation for a hyperbolic orbit:
v_peri² = v_inf² + 2 · GM_earth / r
where v_inf is the hyperbolic excess velocity (input). Speed boost = v_peri − v_inf.
GEO crossing: inside if perigee_km < 42,164 km. GEO margin = GEO_km − perigee_km (positive = inside GEO ring).
JPL/CNEOS Apophis close-approach solution #197 (as of 2024): perigee 38,017 km, diameter ~340 m (radar shape model), v_inf ~7.43 km/s. All solutions since Farnocchia et al. 2021 rule out Earth impact in 2029.
Missions
NASA OSIRIS-APEX (formerly OSIRIS-REx) — en route, arrival 2029-04-13
ESA Ramses — committed Nov 2025, launch target Apr 2028, arrival Apr 2029