Jupiter radius

The Jupiter radius or Jovian radius (plural Jupiter radii or Jovian radii; denoted as R_J or, less commonly, R_Jup) has a value of 71,492 km (44,423 mi), or of 11.2 Earth radii (R_🜨)^[2] (one Earth radius, 6378 km, equals 0.08921 R_J). The Jupiter radius is a unit of length used in astronomy to describe the radii of large planets (especially gas giants) and certain exoplanets. It is also used in describing certain stars, in particular brown dwarfs.

Jupiter radius
The size of Jupiter compared to Earth
General information
Unit system	astronomy
Unit of	length
Symbol	RJ, RJup,R♃
Conversions
1 RJ in ...	... is equal to ...
SI base units	7.1492×107 m[1]
English units	44423 miles

The general shape of the planet Jupiter has been directly measured from radio occultations of passing spacecraft, starting with the Pioneer and Voyager missions. This method gives an overall margin of error of about ±5 km. Estimates of the radius at one bar pressure are then determined through extrapolation. The planet Jupiter has the approximate shape of an oblate spheroid, which is mainly set by the rate of rotation. This gives a difference of about 10% between its polar and equatorial radii. The polar radius has been determined with an accuracy of ±10 km (as of 1987). Density fluctuations within the planet can create variations in the equatorial radius of up to 30 km. The winds in Jupiter's outer atmosphere can vary the radius by up to 4 km.^[3]

In 2015, the International Astronomical Union defined the nominal equatorial Jovian radius as a set number of meters, so that a commonly agreed (or at least known) value would remain constant, notwithstanding any possible subsequent improvements in measurement precision of R_J. This 'constant' is defined as exactly:

${\displaystyle {\mathcal {R}}_{\mathrm {eJ} }^{\mathrm {N} }}$ = 7.1492×10⁷ m

Similarly, the nominal polar Jovian radius is defined to be exactly:

${\displaystyle {\mathcal {R}}_{\mathrm {pJ} }^{\mathrm {N} }}$ = 6.6854×10⁷ m^[1]

These values correspond to the radius of Jupiter at 1 bar of pressure. The common usage—across astronomical objects—is to refer to equatorial radius, unless the polar radius is specifically needed.

Comparison

Radii of noteworthy astronomical objects relative to Jupiter

Object	RJ / Robject	Ref
Lunar radius	41
Earth radius	11.209	[2]
Jupiter	1	by definition
Solar radius	0.10045

For comparison, one solar radius is approximately equal to:

• 400 Lunar radii (R_☾)
• 109 Earth radii (R_🜨)
• 9.955 Jupiter radii (R_J)