Launched in 1977, spacecraft Voyager 1 celebrates 40 years in space on Tuesday.
Its twin spacecraft, Voyager 2, celebrated the same anniversary last month on Aug. 20.
Here’s a look back at some of the many discoveries made by the space probes.
Voyager 1 flew within 277,400 kilometres of Jupiter on March 5, 1979, while Voyager 2 came within 650,180 kilometres on July 9, 1979.
The Voyagers took images that showed plumes from volcanoes on the surface of Io, one of Jupiter’s moons.
It was the first time an active volcano was observed in our solar system beyond Earth.
NASA says Io is “the most volcanically active body in the solar system,” with hundreds of active volcanoes on its surface.
The Voyagers also took images of Europa, another one of Jupiter’s moons.
Those images showed cracks on the surface, which were filled in with a dark, icy material. This was the first hint for scientists of water underneath the surface of Europa.
The Galileo spacecraft mission was launched in 1989, and entered orbit around Jupiter in 1995. Its measurements showed the planet’s magnetic field was disrupted in the space around Europa, which scientists believe is caused by an “electrically conductive fluid” beneath the moon’s surface — most likely an ocean of salt water.
Because of this, many scientists believe Europa is the most likely place to find life outside of Earth in our solar system.
On Aug. 25, 1989, Voyager 2 took the first images of Triton, Neptune’s largest moon.
The photos showed geyser-like eruptions shooting nitrogen gas and dust particles several kilometres into Triton’s atmosphere.
Due to Triton’s relatively high density and retrograde orbit — orbiting in the opposite direction to Neptune’s rotation — scientists determined Triton, like Pluto, was likely not originally from our solar system, and had been captured in Neptune’s orbit.
On Nov. 12, 1980, Voyager 1 flew by Saturn, recording data on the planet and its many moons.
It found that one of the moons, Titan, had a thick atmosphere mostly composed of nitrogen, like Earth’s atmosphere, although the surface pressure was about…