Jupiter radius

{{Short description|Unit of length in astronomy}}

{{Infobox unit

| name = Jupiter radius

| image = Jupiter, Earth size comparison.jpg

| caption = The size of Jupiter compared to Earth

| standard = astronomy

| quantity = length

| symbol = {{Jupiter radius}}

| symbol2 = {{Jupiter radius|jup=y}},{{Jupiter radius|greek=y}}

| units1 = SI base units

| inunits1 = {{val|7.1492|e=7|u=m}}{{cite arXiv |eprint=1510.07674|last1=Mamajek|first1=E. E|title=IAU 2015 Resolution B3 on Recommended Nominal Conversion Constants for Selected Solar and Planetary Properties| last2=Prsa|first2=A|last3=Torres|first3=G|last4=Harmanec|first4=P|last5=Asplund|first5=M|last6=Bennett|first6=P. D|last7=Capitaine|first7=N|last8=Christensen-Dalsgaard|first8=J|last9=Depagne|first9=E|last10=Folkner|first10=W. M|last11=Haberreiter|first11=M|last12=Hekker|first12=S|last13=Hilton|first13=J. L|last14=Kostov|first14=V|last15=Kurtz|first15=D. W|last16=Laskar|first16=J|last17=Mason|first17=B. D|last18=Milone|first18=E. F|last19=Montgomery|first19=M. M|last20=Richards|first20=M. T|last21=Schou|first21=J|last22=Stewart|first22=S. G|class=astro-ph.SR|year=2015|display-authors= 3}}

| units2 = English units

| inunits2 = {{val|44423|ul=miles}}

}}

The Jupiter radius or Jovian radius ({{Jupiter radius}} or {{Jupiter radius|Jup=y}}) has a value of {{convert|71492|km|mi|abbr=on}}, or 11.2 Earth radii ({{Earth radius}}) (one Earth radius equals {{Jupiter radius|0.08921}}). The Jupiter radius is a unit of length used in astronomy to describe the radii of gas giants and some exoplanets. It is also used in describing brown dwarfs.

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 gives an overall margin of error of about 5 km. Estimates of the radii 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 the 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 the outer atmosphere can vary the radius by up to 4 km.{{cite journal

| title=The Shape of Jupiter and Saturn Based on Atmospheric Dynamics, Radio Occultations and Gravity Measurements

| last1=Galanti | first1=E. | last2=Kaspi | first2=Y. | last3=Guillot | first3=T.

| journal=Geophysical Research Letters | volume=50 | issue=6 | id=e2022GL102321

| date=March 2023 | doi=10.1029/2022GL102321

| arxiv=2305.02647 | bibcode=2023GeoRL..5002321G | s2cid=257543496 }}

In 2015, the International Astronomical Union defined the nominal equatorial Jovian radius to remain constant regardless of subsequent improvements in measurement precision of {{Jupiter radius}}. This constant is defined as exactly:

:$\backslash mathcal\{R\}^\backslash mathrm\; N\_\backslash mathrm\; \{eJ\}$ = {{val|7.1492|e=7|u=m}}

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

:$\backslash mathcal\{R\}^\backslash mathrm\; N\_\backslash mathrm\; \{pJ\}$ = {{val|6.6854|e=7|u=m}}

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