Escape Velocity of Mercury
| Value | 4,250 m/s |
| Status | Conventional / typical value |
| Source | Derived from the MESSENGER GM (2.2032 × 10¹³ m³/s²) and the mean radius |
| Categories | Astronomicalsolar-systemplanets |
| millimeter per year | 134,119,800,000,000 mm/yr |
| millimeter per hour | 15,300,000,000 mm/h |
| foot per day | 1,204,724,400 ft/d |
| inch per hour | 602,362,200 in/h |
| meter per day | 367,200,000 m/d |
| millimeter per minute | 255,000,000 mm/min |
| meter per hour | 15,300,000 m/h |
| inch per minute | 10,039,370 in/min |
| millimeter per second | 4,250,000 mm/s |
| foot per minute | 836,614.17 ft/min |
| centimeter per second | 425,000 cm/s |
| meter per minute | 255,000 m/min |
| inch per second | 167,322.83 in/s |
| kilometer per hour | 15,300 km/h |
| foot per second | 13,943.57 ft/s |
| mile per hour | 9,506.9792 mph |
| knot | 8,261.3391 kn |
| meter per second | 4,250 m/s |
| mach (sea level) | 12.489201 Ma |
| kilometer per second | 4.25 km/s |
| speed of light | 0.000014176474 c |
Learning zone
Whether a world keeps an atmosphere is a contest between its escape velocity and the thermal speed of gas molecules, and Mercury loses on both ends: the shallowest gravity well of any planet, and a subsolar surface that reaches 700 K. Any gas released — from the solar wind, from micrometeorite impacts, from the rock itself — random-walks to escape speed within days. What remains is an exosphere so tenuous its atoms never collide, continuously replenished and continuously blown away into a comet-like sodium tail.
Escaping Mercury is easy; reaching it is the hard part. A spacecraft falling sunward gains so much speed that arriving at Mercury slowly enough to orbit costs more delta-v than a mission to Pluto. MESSENGER needed six planetary flybys over six and a half years to bleed off the excess, and BepiColombo needed nine.