Shining close to Jupiter

Author of this article: Luis Utrilla Navarro

Translated into English by: Carlos M. Entrena Utrilla

Adapted by: Alicia Vílchez Bedmar

Ganymede surface photograph on the Galileo mission on 1997.
Ganymede. Galileo mission. 1997. NASA

It was the year 1610 when, in a cold and clear January night, Galileo Galilei observed the presence of various shining objects close to Jupiter. In following nights, he could attest how those objects change their position, which made him infer that they were turning around the giant planet of our solar system.

Even if at first Galileo named those dazzling objects as Medicean stars, it was the German Simon Marius, also self-proclaim discoverer of the same objects, who, opted for naming each of them individually. Following a suggestion by Johannes Kepler, he named the brightest one of them as Ganymede, honoring the son of King Tros.

Ganymede surface photograph on the Galileo mission on 1997.
Ganymede. Galileo mission. 1997. NASA

Legend has it that Ganymede was a beautiful young man dedicated to his education when he was kidnapped by Jupiter, who transfigured him into an eagle to carry him to Olympus, where Ganymede’s intense light shined alongside the many gods of Antiquity.

The name of Ganymede was not accepted internationally until several centuries after the satellite’s discovery.

The largest of the Galilean satellites, it has a diameter of 5,268 km, which makes it the 9th largest object of our solar system, ahead even of the planet Mercury.

Being one of the objects in our solar system with any chances to harbor life, Ganymede has attracted increasing interest from all types of scientists, and to some extent from space enthusiasts, for years.

Images of its craters and geological formations enthuse us since the 1970s, where the Voyager probes sent us the first detailed pictures of its fractured surface.

Launched in 1989, the Galileo probe took a giant step in our knowledge of Jupiter and its satellites. In 2002, it verified the existence of Ganymede’s magnetic field and, a decade after the Hubble, it observed its polar auroras in ultraviolet light. Both of these facts confirm the existence of underground oceans of water and magnesium sulphate.

The latest visitor to Ganymede has been the June space probe, launched in August 2011 with the goal of studying its atmosphere, ionosphere, magnetosphere, and polar ice caps.

Ganymede photographed during Juno mission.
Ganymede, Juno mission. NASA/JPL-Caltech/SwRI/MSSS

Having reached orbit around Jupiter in 2016, Juno sent, on June 7th 2021, new images of Ganymede of singular beauty that unveil a whole new universe of data for our knowledge of our solar system.

On 2022, the JUICE (Jupiter Icy Moons Explorer) space probe will start its long trek towards Ganymede in search of new data that will keep feeding humanity’s old dreams.

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