Callisto is Jupiter’s second largest moon and the third largest moon in our solar system. Its surface is the most heavily cratered of any object in our solar system. Images of Callisto captured by passing spacecraft show bright white spots standing out against darker regions. Scientists think the bright areas are mostly ice and the darker patches are areas where the ice has eroded.
Once thought to be a dead, inactive rocky body, data gathered by the Galileo spacecraft in the 1990s indicate Callisto may have a salty ocean beneath its icy surface. More recent research reveals that this ocean may be located deeper beneath the surface than previously thought, or may not exist at all. If an ocean is present, it’s possible the ocean is interacting with rock on Callisto, creating a potential habitat for life.
Callisto is a moon of Jupiter with a heavily cratered surface of ice and rock.
Callisto is 2.6 times smaller than Earth, and it’s about 289 times smaller than our Sun.
Farther From the Sun Than Earth
Callisto orbits about 1.2 million miles (1.9 million kilometers) from Jupiter, and Jupiter orbits about 484 million miles (778 million kilometers) from our Sun.
A Long Day
A day on Callisto is about 17 Earth days, the same amount of time it takes Callisto to orbit Jupiter once.
A Very Thin Atmosphere
NASA's Galileo spacecraft detected a thin carbon dioxide atmosphere, or exosphere, on Callisto. Later research determined Callisto has hydrogen and oxygen in its atmosphere.
Carbon Dioxide on its Surface
Galileo also found carbon dioxide on Callisto’s surface.
Callisto doesn’t have rings.
Many NASA spacecraft have observed Callisto including Pioneer, Voyager, Galileo, Cassini, New Horizons, Juno and Hubble.
There is evidence of a subsurface ocean on Callisto, putting Callisto on the list of possible places where life could exist beyond Earth.
One of the Bigger Moons
Callisto is Jupiter’s second largest moon after Ganymede and it’s the third largest moon in our solar system.
What is Special About Callisto?
Callisto may have an underground salty ocean making it a potential habitat for life.
Jupiter and its moons are popular subjects for science fiction writers and Callisto is no exception. It appears in several books and in the TV show “Cowboy Bebop,” Callisto has been terraformed and is home to mostly men.
In the 1930s, writer Harl Vincent had Earth and Callisto at war in his novel “Callisto at War.”
Isaac Asimov’s 1940 novel "The Callistan Menace” depicts Callisto as having an atmosphere of carbon dioxide and oxygen with lakes and vegetation. It’s also a deathtrap crawling with giant caterpillars.
Callisto gets a mention in Robert A. Heinlein's 1950 novel “Farmer in the Sky.” The book is mostly about Jupiter’s moon Ganymede, but it discusses an atmosphere being created so colonists can live on Callisto.
Philip K. Dick, author of “Blade Runner” and “The Minority Report” wrote a short story in 1955 called “The Mold of Yancy” about colonists living in a totalitarian society on Callisto.
Lin Carter created a series of eight books in the 1970s called the Callisto series. The books featured a soldier who is teleported to Callisto where he finds an ancient human civilization. In the book Callisto is like Earth, but some sort of illusion makes it seem uninhabitable to outsiders.
In Kim Stanely Robinson’s book “2312,” settlers have colonized Callisto’s giant moon-spanning impact crater Valhalla, starting from its innermost ring. The author envisions windows lining the inward-facing parts of the rings. As the colony grows and residents seek to maintain their space and independence, they settle in the different rings, creating separate colonies in each one.
The moon is also featured in several other books including:
- The “Bio of a Space Tyrant” series by Piers Anthony
- “Callisto: Dystopian Space” by Rob Lopez
- “The Rowan” by Anne McCaffrey
- “The Quiet War” by Paul J. McAuley
- “Blue Mars” and “Galileo’s Dream” by Kim Stanley Robinson
- “Wheelers” by Ian Stewart and Jack Cohen