Voyager 2 transformed our ideas of the moons of Jupiter 40 years ago

Forty years ago today, a NASA spacecraft has revealed solid evidence that an icy moon of Jupiter could accommodate life.

On July 2, 1979, Voyager 2 went through the Jupiter system and discovered a host of surprises, including a series of cracks on the surface of one of Jupiter's moons, Europa. According to NASA, the scenes in the footage of the probe reminded scientists of a crust floating over a thin ocean of waters, but with only a few hours to Jupiter, the unlucky probe could not solve the problem. mystery.

It was only after Galileo's mission to Jupiter from 1995 to 2003 that scientists gathered enough evidence to hypothesize that the Jovian moon hides a subterranean global ocean that could be microbe-friendly, depending on what that it contains. The concept is so compelling that he even hit Hollywood, with the monstrous film "Europa Report" (2013) speculating on what might be hiding under the surface.

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Galileo and his successor, Cassini, at Saturn, together showed a multitude of ice-like moons similar to Jupiter and Saturn that may well carry internal oceans – Enceladus, Titan and Callisto, to name a few. And in recent years, the Hubble Space Telescope has shown intriguing evidence of Europa periodically projecting water into space.

NASA plans to send two probes to Europa in the 2020s. However, internal reports published earlier this year indicate that both missions are in difficulty due to technical and budgetary issues. This week, however, the agency reviewed one of two missions that launched this new tour of interest for Europa: Voyager 2.

This spaceship was launched on August 20, 1977, a few weeks before its twin, Voyager 1. (The Voyager 2 was first launched to follow a favorable trajectory to continue to Uranus and Neptune if funding continued, according to BBC Science Focus Magazine.) The two spacecraft took advantage of a rare alignment of the outer planets to switch from one destination to another in the solar system, starting with Jupiter and Saturn.

The first distant images of Voyager 2's Jupiter were returned on April 24, 1979 and the spacecraft continued to take pictures and data until August 5 of that year, NASA announced. During this period of three and a half months, the spacecraft returned 17,000 images of the planet and its moons.

Voyager 1 had first reached the Jupiter neighborhood, but Jupiter had confirmed many of his twin's discoveries and had done so on his own. Voyager 2 was ordered to fly relatively close to several Jovian moons as Jupiter approached. The largest moons of Jupiter, visible even in a small telescope with a terrestrial background, are Ganymede, Callisto, Io and Europa.

To get an idea of ​​the proximity of Voyager 2 to some of these moons, compare it to the distance between the Earth and our own moon, which is about 388,400 kilometers. Voyager 2 has served Europa and Callisto about half that distance: 205,000 km from Europa and 215,000 km from Callisto. The shuttle flew much closer to Ganymede, barely 62,000 km (38,600 miles).

Voyager 2's work, along with other observations made before and after his trip, helped scientists gather evidence that each of these moons is an oceanic world. The spacecraft also observed very far off Io en route, confirming Voyager 1's observations on active volcanoes, which intrigued planetary scientists of the time.

The immense gravity of Jupiter is the key to all these active moons. The largest planet in the solar system, Jupiter is so big that about 1,300 Earth could hold it. While these natural satellites revolve around the gas giant, Jupiter's tidal forces bend inside the moons and keep them warm. This phenomenon maintains the global oceans assumed on Europa, Callisto and Ganymede and feeds the volcanoes on Io.

Voyager 2 did a lot more with the Jupiter system. The images showing the planet leaving the Space Shuttle confirmed that thin rings surrounded Jupiter, just as had already seen Voyager 1. Voyager 2 also discovered a moon, which Voyager 1 did not have view, in orbit around the rings; the moon will later call Adrastea.

Voyager 1's journey passed beyond Saturn and well above the plane of our solar system, while Voyager 2 continued to sway from planet to planet. This spacecraft passed to Uranus in 1986 and Neptune in 1989, before continuing its journey out of the solar system. Voyager 1 entered interstellar space in 2012 and Voyager 2 in 2018.

Both spacecraft continue to transmit data to the Earth. According to NASA's Jet Propulsion Laboratory, they will continue to send scientific data until about 2025, when their nuclear energy reserves will become too small to support any instrument.

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