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Venus was 0.7205 au from the Sun on the day of transit, decidedly less than average. [9] Moving far backwards in time, more than 200,000 years ago Venus sometimes passed by at a distance from Earth of barely less than 38 million km, and will next do that after more than 400,000 years.
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According to data from the Pioneer Venus Orbiter altimeters, nearly 51% of the surface is located within 500 meters (1,600 feet) of the median radius of 6,052 km (3,761 mi); only 2% of the surface is located at elevations greater than 2 kilometres (1.2 mi) from the median radius.
Vesta (radius 262.7 ± 0.1 km), the second-largest asteroid, appears to have a differentiated interior and therefore likely was once a dwarf planet, but it is no longer very round today. [74] Pallas (radius 255.5 ± 2 km ), the third-largest asteroid, appears never to have completed differentiation and likewise has an irregular shape.
r is the sphere's radius; a is the orbit's semi-major axis in metres, G is the gravitational constant, ρ is the density of the sphere in kilograms per cubic metre. For instance, a small body in circular orbit 10.5 cm above the surface of a sphere of tungsten half a metre in radius would travel at slightly more than 1 mm/s, completing an orbit ...
For planet Earth, which can be approximated as an oblate spheroid with radii 6 378.1 km and 6 356.8 km, the mean radius is = (( ) ) / = . The equatorial and polar radii of a planet are often denoted r e {\displaystyle r_{e}} and r p {\displaystyle r_{p}} , respectively.
The predicted values for the moment of inertia based on planetary models suggest a core radius of 2,900–3,450 km. [74] There is now an estimate of 3,500 km from the moment of inertia based on the rate of axial precession, measured between 2006 and 2020.
The ionosphere of Venus consists of three layers: v1 between 120 and 130 km, v2 between 140 and 160 km and v3 between 200 and 250 km. [28] There may be an additional layer near 180 km. The maximum electron volume density (number of electrons in a unit of volume) of 3 × 10 11 m −3 is reached in the v2 layer near the subsolar point . [ 28 ]