In a mission that changed our understanding of gas giants, NASA’s Galileo spacecraft made history not just in orbit but also in its dramatic descent into Jupiter’s atmosphere. Launched in October 1989, Galileo became the first spacecraft to orbit an outer planet, setting new scientific milestones over its 14-year journey.
The mission provided a unique glimpse into Jupiter’s turbulent environment, its complex magnetosphere, and a family of intriguing moons—before it met its end in a controlled dive that revealed the violent beauty of the solar system’s largest planet.
The First Mission Dedicated To Jupiter’s Deep Secrets
Galileo’s odyssey began with a gravity assist from Venus, offering stunning visuals of the planet’s thick cloud cover before setting course for Jupiter. Upon arrival in 1995, the spacecraft became the first to enter orbit around a gas giant, initiating an ambitious 23-month mission that included 11 orbits and close flybys of major moons.
The data collection far exceeded expectations. Galileo’s journey included 35 encounters with Jupiter’s largest moons: 11 with Europa, eight with Callisto, eight with Ganymede, seven with Io, and one with Amalthea. These close approaches yielded game-changing findings—most notably, intense volcanic activity on Io and compelling evidence of a subsurface ocean on Europa.
Also, Galileo discovered a magnetic field around Ganymede, a phenomenon never before observed on a moon. The spacecraft also captured the only in-space observation of Comet Shoemaker-Levy 9 impacting Jupiter in real time, a moment that marked a first in solar system exploration.
A Probe Through Fire And Pressure
One of the mission’s most extraordinary moments occurred when Galileo released a descent probe into Jupiter’s atmosphere in July 1995. Lacking its own propulsion, the small “wok-shaped” probe fell freely into the planet’s upper atmosphere, hitting at a blistering speed of 170,000 kilometers per hour (106,000 mph)—a velocity NASA likened to that of a comet.
With temperatures rising to twice as hot as the Sun’s surface, the probe endured extreme conditions, braking aerodynamically before deploying a parachute and heat shield. Over the next 58 minutes, it descended about 200 kilometers (125 miles) into the dense Jovian clouds, transmitting valuable data to the orbiting craft. The descent revealed real-time measurements of sunlight, heat flux, pressure, temperature, lightning, winds, and chemical composition.
When the probe’s instruments finally succumbed to the planet’s intense heat, it had already achieved more than twice its planned operational depth, transmitting from a zone where pressure reached 23 times that of Earth’s surface. This data gave scientists vital insight into the chemical makeup of Jupiter.
The Intentional Plunge To Protect A Distant Ocean
Galileo‘s extended mission, which continued well beyond its primary goals, eventually ended in September 2003 with a deliberate plunge into Jupiter’s atmosphere.
The decision to destroy the spacecraft was made to prevent any accidental impact with Europa, whose possible subsurface ocean—revealed by Galileo itself—could potentially harbor life. The spacecraft entered the planet about one-quarter of a degree south of the equator, at a speed of 48.2 kilometers per second (nearly 108,000 mph).
According to NASA, for a hypothetical observer floating among Jupiter’s clouds, Galileo would have appeared to “stream in from a point about 22 degrees above the local horizon,” covering the equivalent distance from Los Angeles to New York City in just 82 seconds.
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