Although Simon Marius is not credited with the sole discovery of the Galilean satellites, his names for the moons were adopted.
In his 1614 publication Mundus Iovialis anno M.DC.IX Detectus Ope Perspicilli Belgici, he proposed several alternative names for the innermost of the large moons of Jupiter, including "The Mercury of Jupiter" and "The First of the Jovian Planets".
Based on a suggestion from Johannes Kepler in October 1613, he also devised a naming scheme whereby each moon was named for a lover of the Greek mythological Zeus or his Roman equivalent, Jupiter.
He named the innermost large moon of Jupiter after the Greek mythological figure Io:
... Inprimis autem celebrantur tres fœminæ Virgines, quarum furtivo amore Iupiter captus & positus est, videlicet Io Inachi Amnis filia... Primus à me vocatur Io... [Io,] Europa, Ganimedes puer, atque Calisto, lascivo nimium perplacuere Jovi.

... First, three young women who were captured by Jupiter for secret love shall be honoured, namely, Io, the daughter of the river Inachus... The first [moon] is called by me Io... Io, Europa, the boy Ganymede, and Callisto greatly pleased lustful Jupiter.

Marius's names were not widely adopted until centuries later (mid-20th century).
In much of the earlier astronomical literature, Io was generally referred to by its Roman numeral designation (a system introduced by Galileo) as "Jupiter I", or as "the first satellite of Jupiter".

The customary English pronunciation of the name is /ˈaɪoʊ/, though sometimes people attempt a more 'authentic' pronunciation, /ˈiːoʊ/. The name has two competing stems in Latin: Īō and (rarely) Īōn.
The latter is the basis of the English adjectival form, Ionian.

Features on Io are named after characters and places from the Io myth, as well as deities of fire, volcanoes, the Sun, and thunder from various myths, and characters and places from Dante's Inferno: names appropriate to the volcanic nature of the surface.
Since the surface was first seen up close by Voyager 1, the International Astronomical Union has approved 225 names for Io's volcanoes, mountains, plateaus, and large albedo features.
The approved feature categories used for Io for different types of volcanic features include patera ("saucer"; volcanic depression), fluctus ("flow"; lava flow), vallis ("valley"; lava channel), and active eruptive center (location where plume activity was the first sign of volcanic activity at a particular volcano).
Named mountains, plateaus, layered terrain, and shield volcanoes include the terms mons, mensa ("table"), planum, and tholus ("rotunda"), respectively.
Named, bright albedo regions use the term regio.
Examples of named features are Prometheus, Pan Mensa, Tvashtar Paterae, and Tsũi Goab Fluctus.
Although Simon Marius is not credited with the sole discovery of the Galilean satellites, his names for the moons were adopted. In his 1614 publication Mundus Iovialis anno M.DC.IX Detectus Ope Perspicilli Belgici, he proposed several alternative names for the innermost of the large moons of Jupiter, including "The Mercury of Jupiter" and "The First of the Jovian Planets". Based on a suggestion from Johannes Kepler in October 1613, he also devised a naming scheme whereby each moon was named for a lover of the Greek mythological Zeus or his Roman equivalent, Jupiter. He named the innermost large moon of Jupiter after the Greek mythological figure Io:
... Inprimis autem celebrantur tres fœminæ Virgines, quarum furtivo amore Iupiter captus & positus est, videlicet Io Inachi Amnis filia... Primus à me vocatur Io... [Io,] Europa, Ganimedes puer, atque Calisto, lascivo nimium perplacuere Jovi.
... First, three young women who were captured by Jupiter for secret love shall be honoured, namely, Io, the daughter of the river Inachus... The first [moon] is called by me Io... Io, Europa, the boy Ganymede, and Callisto greatly pleased lustful Jupiter.
Marius's names were not widely adopted until centuries later (mid-20th century). In much of the earlier astronomical literature, Io was generally referred to by its Roman numeral designation (a system introduced by Galileo) as "Jupiter I", or as "the first satellite of Jupiter".
The customary English pronunciation of the name is /ˈaɪoʊ/, though sometimes people attempt a more 'authentic' pronunciation, /ˈiːoʊ/. The name has two competing stems in Latin: Īō and (rarely) Īōn. The latter is the basis of the English adjectival form, Ionian.
Features on Io are named after characters and places from the Io myth, as well as deities of fire, volcanoes, the Sun, and thunder from various myths, and characters and places from Dante's Inferno: names appropriate to the volcanic nature of the surface. Since the surface was first seen up close by Voyager 1, the International Astronomical Union has approved 225 names for Io's volcanoes, mountains, plateaus, and large albedo features. The approved feature categories used for Io for different types of volcanic features include patera ("saucer"; volcanic depression), fluctus ("flow"; lava flow), vallis ("valley"; lava channel), and active eruptive center (location where plume activity was the first sign of volcanic activity at a particular volcano). Named mountains, plateaus, layered terrain, and shield volcanoes include the terms mons, mensa ("table"), planum, and tholus ("rotunda"), respectively. Named, bright albedo regions use the term regio. Examples of named features are Prometheus, Pan Mensa, Tvashtar Paterae, and Tsũi Goab Fluctus.
Io (moon)