Most of what we know about Io comes from Galileo spacecraft, which made a detailed study of the Jupiter system—including Io—from orbit from December 1995 to September 2006, but it was Voyager 1 that spotted the first signs of the little moon’s powerful volcanism in 1979. Since 2003, three spacecraft—Ulysses, Cassini, New Horizons and Juno—have made additional close observations of Io. Juno is currently orbiting Jupiter, but its prime mission is focused on the giant planet, not the moons.

Significant Events

Significant Events

  • Dec. 8, 1610: Galileo Galilei makes the first recorded observations of Io and three more moons orbiting Jupiter.
  • 1973-1974: Pioneer 10—the first spacecraft to explore Jupiter up close—and its sister mission, Pioneer 11, make the first close-up measurements of Io.
  • March 1979: Voyager 1 catches a volcanic eruption in the act during its Jupiter flyby.
  • July 1979: Voyager 2 takes additional images and captures more science data during a more distant flyby of Io.
  • 1992: Scientists are surprised when the Ulysses spacecraft—using Jupiter to hurtle itself into an obrit to study the poles of the Sun—passes through a fast-moving stream of particles from Io—faster than most other particles found in the solar system.
  • 1995-2002: The Galileo spacecraft makes detailed observations of Io during multiple flybys, providing the closest views to date of the tortured moon.
  • 2000: The Cassini spacecraft studies Io while passing by Jupiter en route to Saturn.
  • 2007: New Horizons documents Io’s ever changing surface in images that are compared to Galileo images back on Earth.
Notable Explorers



10 Careers That Explore Space



Astronauts pave the way for human exploration beyond our Earth. They are pilots, scientists, engineers, teachers, and more.


Project Manager

Project managers guide missions from concept to completion, working closely with team members to accomplish what they set out to do.  


Rover Camera Operator

A camera payload uplink lead writes software commands that tell a rover what pictures to take.

The first thing that fired my imagination for planetary science was when the NASA Voyager spacecraft discovered active volcanoes on Jupiter's moon Io.



Melding science with design, artists create everything from large-scale installations to the NASA posters hanging in your bedroom. 


Media Specialist

Media specialists tells stories across social media and help feature missions and people on TV and in films, books, magazines, and news sites. 



Writers/producers capture the incredible stories of NASA's missions and people and share them with the world. 



Administrators and directors work out of NASA headquarters, prioritizing science questions and seeking to expand the frontiers of discovery.



Whether it's introducing kids to space or teaching physics to PhD candidates, educators help share their knowledge with the public.



Engineers design and build all types of machines, from what a spacecraft looks like to the software that directs where a rover goes each day. 



From an astrophysicist to a volcanologist, scientists of all types pose questions and help find answers to the mysteries of our universe.

The important thing about being a scientist or an engineer is learning how to think critically, learning how to be creative, learning problem solving and learning how to learn.

Explore in 3D

Eyes on the Solar System Ad

Explore in 3D—Eyes on the Solar System

Eyes on the Solar System lets you explore the planets, their moons, asteroids, comets and the spacecraft exploring them from 1950 to 2050. Ride with the Curiosity Rover as it lands on Mars or fly by Pluto with the New Horizons spacecraft all from the comfort of your home computer.

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