Is There Life On Ganymede?

It is possible for certain types of life to exist on Ganymede due to subsurface oceans, but we do not have evidence of life at this time.

Josh Habka

Dec 22, 2022

8 min read

home, Solar System, Jupiter's Moons

Ganymede is considerably larger than Europa, the most volcanic body in the sky, and every other moon around the entire Solar System. However, Ganymede is missing one crucial life-sustaining element. Ganymede is similar to most of the moons in our solar system because it is tidally locked with Jupiter, showing just one face at all times.

The third largest moon out of the 79 Jovian moons, Ganymede also is the only moon with its own magnetic field. Outwardly pointing away from Jupiter, Ganymede is the seventh satellite and the third of the Galilean moons, the first group of objects discovered orbiting another planet. Ganymede is an enormous natural satellite located about 665,000 miles (more than one million kilometers) away from Jupiter - a planet that it circles for seven days and three hours each revolution.

Ganymede is considered to be a low-density moon, although it is larger than the planet Mercury. The moon's atmosphere is far too thin to support life as we know it, but these discoveries indicate Ganymede is more Earth-like than most of the planets in our own Solar System, perhaps except for Mars.

Ganymede is a more stable theoretical home for life. Ganymede would have been warmed up from Jupiter's tidal heating long after Ganymede's core had cooled. A thick ice cover would have protected any sea-based life from an asteroid impact like that which destroyed the dinosaurs. Trapped under thick layers of ice, and affected by an extensive internal magnetic field, Ganymede, Jupiter's moon, has thick, subsurface, liquid-water oceans, which must directly interface with the rocky mantle under alternate layers of ice and water, potentially providing an impressively fertile environment for life to emerge, and could thus potentially support indefinitely. With these intrinsic properties, the Jovian moon Ganymede suddenly changes from being a barren world, similar to the moon on Earth, to having possibly the best chances of sustaining life within its deep-underground ocean at the interface between its lower-level liquid ocean and its warm, rocky mantle.

Whether or not life exists on the largest Jovian moon, Ganymede, will need to be studied over the coming decades. However, just like Europa and Enceladus, it has substantial potential for habitability.

While the mission will study its satellites, the main target will be Jupiter's moon Ganymede, as it shows how ice worlds can develop and may be habitable, according to the European Space Agency's website. The European Space Agency is launching JUpiter ICy Moons Explorer, which will start exploring Ganymede and two other moons, Callisto and Europa, in 2030. As mentioned, the JUICE (Jupiter Icy Moons Explorer) probe will be the next main Ganymede-exploration mission.

This discovery increases the expectations for the next Jupiter Icy Moons Explorer (JUICE) mission by the European Space Agency, the first major mission of the ESA's 2015-2025 Cosmic Vision program. Ganymede's icy nature makes it a target of the European Space Agency's (ESA) next mission, JUICE, for Jupiter Icy Moons Explorer.

Ganymede represents one of a number of icy satellites in the outer solar system, providing scientists the chance to explore habitability at unlikely locations. Icy moons such as Ganymede and Enceladus might not resemble the Earth, but they may be habitable in their own ways. On the other hand, Ganymede is the largest moon in the entire Solar System, and while Ganymede has water and ice as well, Europa might be the better choice for travel.

Europa is the most habitable of all of the moons that orbit Jupiter and has a few Earth-like characteristics. Between Europa and Ganymede, Europa has attracted scientists immediate attention in search of life, as well as being one of the best candidates for the entire Solar System.

Ganymede could host a salty ocean, which is located beneath the ice we detect at its surface. Just as we have a unique collection of extremophile organisms that flourish around, and are uniquely adapted to, the environments surrounding hydrothermal vents here on Earth, it is entirely possible that something very, very similar is going on 800 kilometers below, at the ocean/mantle interface, on Jovian Moon Ganymede.

The discovery of water vapor and oxygen on Ganymede tells us that its surface is indeed reacting with space weather hitting it, and that is in spite of Jupiter's powerful magnetic field. Astronomers used archived data sets from NASA/ESA Hubble Space Telescope to uncover the first evidence of water vapor in Jupiter's Ganymede moons atmosphere, a result of the thermal venting of water vapor off the icy moon's surface. The atmospheric venting of water vapor off the icy surface of Jupiter's Ganymede moon.

The Hubble space telescope, in orbit around Earth, discovered a tenuous oxygen atmosphere around Ganymede. Additional evidence for an oxygen atmosphere came from the spectral discovery of gases trapped within Ganymede's surface ice. In 1998, the Space Telescopes Hubble Image Spectrograph (STIS) took the first UV (ultraviolet) image of Ganymede, revealing a peculiar pattern in the observable emissions of the moon's atmosphere.

Despite the Galileo-Galilei data, evidence of a tenuous oxygen atmosphere (exosphere) on Ganymede, much like that found on Io, was found in 1995 by the Hubble Space Telescope (HST). The oxygen is not evidence of life; it is thought to have been produced when the water ice on Ganymede's surface was divided by radiation into hydrogen and oxygen, the hydrogen being lost most quickly afterward because of its lower atomic mass. Another concern is that, even if life had somehow managed to form at Ganymede, it would have been extremely difficult to detect beneath the other ice layers.

This means that Ganymede has the potential for evolving marine life similar to those found in Earth's deep seas, living on the undersea thermal vents.

NASA's Galileo spacecraft made a key discovery, Jupiter's moon Ganymede has its own magnetosphere -- the region of charged particles that surrounds many planets but has never been found around a moon. In 1995, Galileo passed by Ganymede at an extremely low altitude of 162 miles/261 kilometers in order to observe the surface of the Galilean moon. A magnetic dipole has cut out part of space around Ganymede, creating a small magnetosphere embedded within the one at Jupiter; it is the only moon known to have this characteristic in the solar system.

Scientists will attempt to understand more about Ganymede, the Jovian moon, by mapping its icy surface in detail, learning about its interior, probing its atmosphere, and studying its magnetic field.