Escape speed
From CreationWiki, the encyclopedia of creation science
The escape speed associated with any celestial body, such as a star, a planet, a dwarf planet, or a moon, is the speed at which an object, starting from the body surface, would have to travel to be able to escape the body's gravity. An object in motion may be said to have escaped the gravity of a celestial body if the body cannot cause the object to fall back toward it or to remain in orbit around it.
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Concept
The term "escape velocity" is sometimes used. This term is in error. Escape speed is a scalar, not a vector. An object in motion with respect to a celestial body need not be moving directly away from that body in order to escape it.
When an object is traveling exactly at escape speed, it is following a parabolic path with the body at the focus of the parabola. A parabolic path is open; hence an object following such a path will never return to the body.
An object traveling at a speed slower than the escape speed normally moves in an ellipse, which is a closed path. So long as that path does not intersect the body surface, the path is an orbit.
An object traveling faster than escape speed is following a hyperbolic path, and therefore will always be traveling faster than a minimum speed even after infinite time.
Calculation
Escape speed depends on two properties of the body to be escaped from: its mass and its radius. In fact, a body has an escape speed from its surface and from any altitude above that surface. The classical "escape speed" of any body is the escape speed from its surface. Once an object achieves orbit, the escape speed required to break out of orbit is considerably less than the escape speed from the surface.
The formula for escape speed, depending on body mass and radius, is:
The formula that depends on surface gravity is simpler:
where g = surface gravity.
Table
The following table lists several celestial bodies for which the escape speed is known:
| Name | Mass | Mean radius | Equatorial radius | Surface gravity | Escape speed |
|---|---|---|---|---|---|
| Deimos | 62006.2 km3.853 mi | 0.00252.54929e-4 g0.0025 m/s² 0.0082 ft/s² |
5.60.0056 km/s20.16 km/h 0.00348 mi/s 12.527 mph |
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| Phobos | 1110011.1 km6.897 mi | 0.005815.92455e-4 g0.00581 m/s² 0.0191 ft/s² |
11.40.0114 km/s41.04 km/h 0.00708 mi/s 25.501 mph |
||
| Miranda | 234200234.2 km145.525 mi | 240000240 km149.129 mi | 0.08020.00818 g0.0802 m/s² 0.263 ft/s² |
1940.194 km/s698.4 km/h 0.121 mi/s 433.966 mph |
|
| Ceres | 487300487.3 km302.794 mi | 0.270.0275 g0.27 m/s² 0.886 ft/s² |
5100.51 km/s1,836 km/h 0.317 mi/s 1,140.838 mph |
||
| Charon | 586000586 km364.124 mi | 0.2780.0283 g0.278 m/s² 0.912 ft/s² |
5800.58 km/s2,088 km/h 0.36 mi/s 1,297.423 mph |
||
| Pluto | 11950001,195 km742.539 mi | 0.580.0591 g0.58 m/s² 1.903 ft/s² |
12001.2 km/s4,320 km/h 0.746 mi/s 2,684.324 mph |
||
| Eris | 13000001,300 km807.783 mi | 0.80.0816 g0.8 m/s² 2.625 ft/s² |
14421.442 km/s5,191.2 km/h 0.896 mi/s 3,225.662 mph |
||
| Triton | 13534001,353.4 km840.964 mi | 0.779550.0795 g0.78 m/s² 2.558 ft/s² |
1452.61.453 km/s5,229.36 km/h 0.903 mi/s 3,249.374 mph |
||
| Europa | 15608001,560.8 km969.836 mi | 1.32390.135 g1.324 m/s² 4.344 ft/s² |
20202.02 km/s7,272 km/h 1.255 mi/s 4,518.611 mph |
||
| Moon | 17371001,737.1 km1,079.384 mi | 17381001,738.1 km1,080.005 mi | 1.620.165 g1.62 m/s² 5.315 ft/s² |
23802.38 km/s8,568 km/h 1.479 mi/s 5,323.908 mph |
|
| Callisto | 24103002,410.3 km1,497.691 mi | 1.235770.126 g1.236 m/s² 4.054 ft/s² |
24502.45 km/s8,820 km/h 1.522 mi/s 5,480.494 mph |
||
| Io | 18216001,821.6 km1,131.89 mi | 1.796110.183 g1.796 m/s² 5.893 ft/s² |
2558.052.558 km/s9,208.98 km/h 1.589 mi/s 5,722.195 mph |
||
| Titan | 25755002,575.5 km1,600.342 mi | 1.35350.138 g1.354 m/s² 4.441 ft/s² |
2640.52.641 km/s9,505.8 km/h 1.641 mi/s 5,906.63 mph |
||
| Ganymede | 26312002,631.2 km1,634.952 mi | 1.42820.146 g1.428 m/s² 4.686 ft/s² |
2741.52.742 km/s9,869.4 km/h 1.703 mi/s 6,132.561 mph |
||
| Mercury (planet) | 3.3E+233.3e+23 kg0.0552 M⊕ 1.73803e-4 M♃ |
24397002,439.7 km1,515.959 mi | 2.780.283 g2.78 m/s² 9.121 ft/s² |
42504.25 km/s15,300 km/h 2.641 mi/s 9,506.979 mph |
|
| Mars | 6.4185E+236.4185e+23 kg0.107 M⊕ 3.38047e-4 M♃ |
34025003,402.5 km2,114.215 mi | 3.720.379 g3.72 m/s² 12.205 ft/s² |
50205.02 km/s18,072 km/h 3.119 mi/s 11,229.42 mph |
|
| Venus | 4.8685E+244.8685e+24 kg0.815 M⊕ 0.00256 M♃ |
60518006,051.8 km3,760.414 mi | 8.870.904 g8.87 m/s² 29.101 ft/s² |
1036010.36 km/s37,296 km/h 6.437 mi/s 23,174.66 mph |
|
| Earth | 5.9736E+245.9736e+24 kg1 M⊕ 0.00315 M♃ |
63710006,371 km3,958.756 mi | 63781356,378.135 km3,963.189 mi | 9.7803270.997 g9.78 m/s² 32.088 ft/s² |
1118611.186 km/s40,269.6 km/h 6.951 mi/s 25,022.369 mph |
| Uranus | 8.6832E+258.6832e+25 kg14.53 M⊕ 0.0457 M♃ |
2536200025,362 km15,759.216 mi | 2555900025,559 km15,881.626 mi | 8.690.886 g8.69 m/s² 28.51 ft/s² |
2130021.3 km/s76,680 km/h 13.235 mi/s 47,646.743 mph |
| Neptune | 1.0243E+261.0243e+26 kg17.14 M⊕ 0.0539 M♃ |
2462200024,622 km15,299.401 mi | 2476400024,764 km15,387.636 mi | 111.122 g11 m/s² 36.089 ft/s² |
2350023.5 km/s84,600 km/h 14.602 mi/s 52,568.003 mph |
| Saturn | 5.6846E+265.6846e+26 kg95.124 M⊕ 0.299 M♃ |
6026800060,268 km37,448.799 mi | 9.050.923 g9.05 m/s² 29.692 ft/s² |
3549035.49 km/s127,764 km/h 22.052 mi/s 79,388.869 mph |
|
| Jupiter | 1.8987E+271.8987e+27 kg317.721 M⊕ 1 M♃ |
7149200071,492 km44,423.069 mi | 20.872.128 g20.87 m/s² 68.471 ft/s² |
5954059.54 km/s214,344 km/h 36.996 mi/s 133,187.187 mph |
|
| Sun | 696000000696,000 km432,474.35 mi | 695500000695,500 km432,163.664 mi | 27427.94 g274 m/s² 898.95 ft/s² |
617700617.7 km/s2,223,720 km/h 383.821 mi/s 1,381,755.548 mph |
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