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Mercury has an orbital speed of 47.4 km/s (29.5 mi/s), whereas Earth's orbital speed is 29.8 km/s (18.5 mi/s). [112] Therefore, the spacecraft must make a larger change in velocity ( delta-v ) to get to Mercury and then enter orbit, [ 187 ] as compared to the delta-v required for, say, Mars planetary missions .
Approximately four (Earth) days before perihelion, the angular speed of Mercury's orbit exactly matches its rotational velocity, so that the Sun's apparent motion stops. At perihelion, Mercury's orbital angular velocity slightly exceeds the rotational velocity, making the Sun appear to go retrograde.
Rotation period with respect to distant stars, the sidereal rotation period (compared to Earth's mean Solar days) Synodic rotation period (mean Solar day) Apparent rotational period viewed from Earth Sun [i] 25.379995 days (Carrington rotation) 35 days (high latitude) 25 d 9 h 7 m 11.6 s 35 d ~28 days (equatorial) [2] Mercury: 58.6462 days [3 ...
Here, the ratio of the rotation period of a body to its own orbital period is some simple fraction different from 1:1. A well known case is the rotation of Mercury, which is locked to its own orbit around the Sun in a 3:2 resonance. [2] This results in the rotation speed roughly matching the orbital speed around perihelion. [14]
In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter (the combined center of mass) or, if one body is much more massive than the other bodies of the system combined, its speed relative to the center of mass of the most massive body.
This occurs because, from approximately four Earth days before perihelion until approximately four Earth days after it, Mercury's angular orbital speed exceeds its angular rotational velocity. [5] Mercury's elliptical orbit is farther from circular than that of any other planet in the Solar System, resulting in a substantially higher orbital ...
Mercury, the closest planet ... the length of its day will decrease to about 3 hours and its equatorial rotation velocity will speed up to about 40 km/s. [28] ...
Precession is a change in the orientation of the rotational axis ... If the speed of the rotation and the ... of the planet Mercury and that predicted by ...