Is There Life? Jupiter's Moon Has Layers Like an Icy Onion
Artist’s interpretation of Ganymede’s interior, based on new NASA-funded models.
Credits: NASA/Science Channel
On August 4, the much-anticipated "Wonders of the Solar System" documentary will premier on the Science Channel.
Presenter and physicist Prof. Brian Cox will show you the hidden mysteries of our interplanetary neighborhood, as well as breathtaking sights of the planets, moons and the sun. Cox will also examine some of Earth's extreme environments to see how life has adapted, perhaps helping us understand whether life can exist elsewhere in our solar system. To provide a taster of what you can expect from "Wonders," Discovery News has gathered some facts, figures and the best images of our solar system to assemble a special Wide Angle supporting this groundbreaking documentary. Let's begin, in the orbit of the solar system's biggest planet, Jupiter...
Moons of Jupiter: Io
Welcome to Jupiter, the solar system's biggest planet and host to more than 63 peculiar moons -- a steady contender for moons compared to satellite-strewn Saturn. From sulfur-spewing furnaces to ice-encrusted oceans, these Jovian satellites are anything but normal! Browse through 10 of our favorites here. If you're looking for a fiery, volcanic spectacle, head to Io, the innermost of Jupiter's "big four" moons. Jupiter's gravity pulls at Io so strongly that the land has tides of up to 300 feet (100 meters). This gravitational tug-of-war produces scorching heat and raises more volcanic activity here than anywhere else in the solar system. Io has a sulfurous surface, and its volcanoes spew silicate magma, causing the hellish moon's surface look like a pizza.
Moons of Jupiter: Metis
While it doesn't look like much in this image (the highest-resolution available!), Metis is Jupiter's closest companion -- for now. It's orbiting the gas giant at a distance of just 75,500 miles (128,000 kilometers) and moving faster than Jupiter spins. Metis is so close to Jupiter's surface, in fact, that it will gradually succumb to the planet's gravity and plunge into its churning clouds. This same principle applies to man-made satellites orbiting the Earth; if their orbit is too low, they'll eventually fall.
Moons of Jupiter: Adrastea
Like Metis, Adrastea is on its way down, eventually: Its orbit is just 1,000 kilometers (621 miles) outside of its fellow doomed moon. The two bodies probably provide lots of the material making up Jupiter's main ring, shown in this Galileo spacecraft image. Adrastea is also tiny at a wee 12 miles (20 kilometers) in diameter.
Moons of Jupiter: Ganymede
If Ganymede orbited the sun instead of Jupiter, it would be a planet of its own -- it's even bigger than Mercury. Its interior is made from layers surrounding a rocky core, and its surface is covered in water ice. Although Ganymede doesn't have much of an atmosphere, it does have some ozone gas near its surface. This gas comes from charged particles in Jupiter's magnetic field smacking into the moon's icy crust.
Credit: Courtesy of Damien Perrotin
Moons of Jupiter: Themisto
We're not entirely sure what Themisto looks like, but scientists know it one odd little satellite. Unlike most other moons, Themisto is oblong and doesn't fit into the traditional groups of Jovian moons. Because this body is so small -- just 5 miles (8 kilometers) in diameter -- astronomers in 2000 confused it for a new object when it was originally found in 1975. Shown here is a speculative illustration of how the irregular moon might be shaped.
Moons of Jupiter: Callisto
Along with Io, Ganymede, and Europa (which is yet to come in this slide show), Callisto is one of the four Galilean satellites. These are the moons of Jupiter that Galileo discovered while looking through a telescope in 1610. Callisto is about the same size as Mercury, and it's a heavily cratered moon that has almost no geological activity. Callisto's surface may also be one of the oldest landscapes in the solar system, including Earth's moon -- about 4 billion years old.
Moons of Jupiter: Thebe
Along with Metis and Adrastea, Thebe was discovered by scientists studying images from the Voyager spacecraft in 1979 and 1980. It's closer to Jupiter than Io is, but it's not so close that it's in danger of losing its altitude. The material in Jupiter's Gossamer ring probably comes from Thebe and another moon, Amalthea.
Credit: NASA/Michael Carroll
Moons of Jupiter: Amalthea
Speaking of Amalthea, shown here is an artist's rendition of the mysterious moon (inset: our best real view so far). Astronomers don't know much about it, but they do know it's the reddest body in the solar system. Unlike the other three moons that lie within Io's orbit -- Thebe, Metis and Adrastea -- Amalthea wasn't discovered by the Voyager science team. Edward Emerson Barnard discovered Amalthea it in 1892, and it had been almost 300 years since anyone had discovered a new moon orbiting Jupiter. Before that, the last person to discover a Jovian moon was Galileo.
Credit: University of Hawaii/Scott Sheppard/D
Moons of Jupiter: S/2000 J11
This not-to-be-named moon marks an interesting dividing line in the wealth of satellites orbiting Jupiter. S/2000 J11, named after it was found in 2000, moves in the same direction that Jupiter spins -- as do all the moons that are closer to the planet. Almost every distant moon, however, orbits in the opposite (retrograde) direction, as this diagram shows. The only known exception is Carpo, sometimes known as Karpo, which was discovered in 2003.
Moons of Jupiter: Europa
About two-thirds of the Earth is covered in water, but Europa has about twice as much water as our home planet. Europa's might surface is covered in ice, but astronomers are almost convinced there is an ocean of liquid water underneath -- an environment shielded from Jupiter's intense radiation that might be hospitable to life. A cold, salty planet might not seem like a good place to live, but there are species on Earth that thrive in just those conditions.
Slideshow originally posted Feb. 2009.
Is There Life? Jupiter's Moon Icy Onion-Like Layers
We don’t hear a lot about Ganymede these days, not with Titan, Enceladus and Europa often stealing the science spotlight. Which is unfortunate because one: Ganymede is really fascinating in its own right, and two: it’s the biggest moon in the solar system – even bigger than the planet Mercury! So even though giant Ganymede may not have a Titanic atmosphere or impressive jets like Enceladus, it does have surprisingly complex subsurface layers “like a club sandwich,” according to new NASA-funded research.
Or, if you prefer my titular reference to a certain animated ogre, like an onion. (Or maybe even a parfait?) Except at the Ganymede deli, the sandwich (or onion) is made up of alternating layers of ice and liquid water, increasing in saltiness with depth.
See a labeled version of the illustration below:
Model of Ganymede’s internal layers (annotated). NASA/JPL-Caltech
“This is good news for Ganymede,” said Steve Vance of NASA’s Jet Propulsion Laboratory in Pasadena. “Its ocean is huge, with enormous pressures, so it was thought that dense ice had to form at the bottom of the ocean. When we added salts to our models, we came up with liquids dense enough to sink to the sea floor.”
The idea of an internal ocean on Ganymede isn’t new; previous models of its interior suggested a single layer of water between an icy crust and an ice-covered, rocky core.
While that would have meant a considerable amount of liquid water inside Ganymede, it also isolated the water from the moon’s rocky layer — eliminating much of the surface area where water/rock chemical processes could occur and potentially create environments conducive for life.
This new model, based on the complex behavior of salt — in Ganymede’s case, magnesium sulfate — in water under increasing pressures puts a layer of liquid water just above the moon’s rocky seafloor, increasing the chances that primitive life could have evolved there.
Of course, that would require not only the right conditions but also the conditions to have been present for a considerable amount of time.
“We don’t know how long the Dagwood-sandwich structure would exist,” said Christophe Sotin of JPL, who along with Vance is a member of the Icy Worlds team at JPL. ”This structure represents a stable state, but various factors could mean the moon doesn’t reach this stable state.”
Still, even if this icy sandwich structure hasn’t remained stable on Ganymede, it’s a viable model for conditions on other similarly icy moons… or even on other planets outside our solar system.