Jupiter's Moon Io
Jupiter's Moon Europa
Europa's surface is mostly water ice, and there is evidence that it may be covering an ocean of water or slushy ice beneath. Europa is thought to have twice as much water as does Earth. This moon intrigues astrobiologists because of its potential for having a "habitable zone." Life forms have been found thriving near subterranean volcanoes on Earth and in other extreme locations that may be analogues to what may exist on Europa.
Europa's Profile:
Age: Europa is estimated to be about 4.5 billion years old.
Distance from the sun: On average, Europa's distance from the sun is about 485 million miles (or 780 million kilometers).
Distance from Jupiter: Europa is Jupiter's sixth satellite. Its orbital distance from Jupiter is 414,000 miles (670,900 km).
Size: Europa is 1,900 miles (3,100 km) in diameter, making it smaller than Earth's moon. It is the 15th largest body in the solar system, and the smallest of the Galilean moons.
Temperature: Europa's surface temperature at the equator never rises above minus 260 degrees Fahrenheit (minus 160 degrees Celsius). At the poles of the moon, the temperature never rises above minus 370 F (minus 220 C).
Io is the most volcanically active body in the solar system. Io's surface is covered by sulfur in different colorful forms. As Io travels in its slightly elliptical orbit, Jupiter's immense gravity causes "tides" in the solid surface that rise 100 m (300 feet) high on Io, generating enough heat for volcanic activity and to drive off any water. Io's volcanoes are driven by hot silicate magma.
Jupiter has 67 known moons. The four largest moons are called the Galilean satellites, after Italian astronomer Galileo Galilei, who observed them in 1610. The German astronomer Simon Marius claimed to have seen the moons around the same time, but he did not publish his observations and so Galileo is given the credit for their discovery. Some of Jupiter's moons, especially Europa, are believed to have the potential of hosting life.
Callisto's surface is extremely heavily cratered and ancient -- a visible record of events from the early history of the solar system. However, the very few small craters on Callisto indicate a small degree of current surface activity.
Jupiter's Moon Callisto
Callisto's Profile:
Age: About 4.5 billion years old.
Distance from Jupiter: Callisto is the outermost of the Galilean moons. Because of its orbiting distance from Jupiter (about 1,168,000 miles) it takes about seven Earth days to make one complete orbit of the planet.
Size: At 3,000 miles (4,800 km) in diameter, Castillo is roughly the same size as Mercury. It is the third largest moon in the entire solar system. It has the lowest density of the four Galilean moons.
Temperature: The mean surface temperature of Callisto is -218.47 Fahrenheit.
Ganymede is the largest moon in the solar system (larger than the planet Mercury), and is the only moon known to have its own internally generated magnetic field.
Jupiter's Moon Ganymede
Ganymede's Profile:
Age: Ganymede is about 4.5 billion years old.
Distance from Jupiter: Ganymede is the seventh moon and third Galilean satellite outward from Jupiter, orbiting at about 665,000 miles (1.070 million km). It takes Ganymede about seven Earth days to orbit Jupiter.
Size: Ganymede’s mean radius is 1,635 miles (2,631.2 km). Due to its size, Ganymede can be viewed with the naked eye. Although Ganymede is larger than Mercury it only has half its mass, classifying it as low density.
Temperature: Daytime temperatures on the surface average -171F to -297F, and night temperatures drop to -193C. It is unlikely that any living organisms inhabit Ganymede.
Our solar system's ruling giant planet Jupiter and 3 of its 4 large Galilean moons are captured on January 24. Image Credit & Copyright: NASA, ESA, and the Hubble Heritage Team
Io's Profile:
Age: Io is about 4.5 billion years old, about the same age as Jupiter.
Distance from Jupiter: Io is the fifth moon from Jupiter. Its orbital distance is about 262,000 miles (422,000 km). Io takes 1.77 Earth days to orbit Jupiter. The same side of Io always faces Jupiter.
Size: Io has a mean radius of 1,131.7 miles, making it slightly larger than the Earth’s moon. Among the Galilean satellites, Io ranks third, behind Ganymede and Callisto but ahead of Europa, in both mass and volume.
Temperature: Io's surface temperature averages about negative 202 degrees F, resulting in the formation of sulfur dioxide snowfields. But Io’s volcanoes can reach 3,000 degrees F. Io is often referred to as a celestial body of fire and ice.
This picture, an attempt to show how Io would appear in the "true colors" perceptible to the average human eye, was taken in 1999 July by the Galileo spacecraft that orbited Jupiter from 1995 to 2003. Image Credit & Copyright: Galileo Project, JPL, NASA
The Discovery of Io
Io was the first of Jupiter’s moons discovered byGalileo Galilei on Jan. 8, 1610. He actually discovered the moon the day prior, but could not differentiate between Io and Europa, another Jupiter moon, until the next night. The discovery, along with three other Jovian moons, was the first time a moon was discovered orbiting a planet other than Earth. Galileo’s discovery eventually led to the understanding that planets orbit the sun, instead of our solar system revolving around Earth.
Exploration of Io
Several spacecraft have flown by Jupiter and its moons. Pioneer 10 arrived first, in 1973, followed by Pioneer 11 in 1974. Voyager 1 and Voyager 2 returned striking photos during their flybys. The Galileo spacecraft passed as low as 162 miles (261 km) over the surfaces of the Galilean moons and produced detailed images.
Io gliding past Jupiter captured by the Cassini spacecraft, offering a stunning demonstration of the ruling planet's relative size. Image Credit & Copyright: Cassini Imaging Team, SSI, JPL, ESA, NASA
Europa: Where life may evolve?
The presence of water beneath the moon's frozen crust makes scientists rank it as one of the best spots in the solar system with the potential for life to evolve. The icy depths of the moons are thought to contain vents to the mantle much as oceans on Earth do. These vents could provide the necessary thermal environment to help life evolve.
Discovery
Galileo Galilei discovered Europa on Jan. 8, 1610. It is possible that German astronomer Simon Marius (1573-1624) also discovered the moon at the same time. However, it is Galileo who is most often credited with the discovery. For this reason, Europa and Jupiter's other three largest moons are often called the Galilean moons.
Exploration of Europa
The Galileo mission, launched by NASA in 1989, is responsible for much of the information we have on Jupiter and the bodies surrounding it. It took more than six years for the unmanned Galileo spacecraft to reach its destination. The craft stayed in orbit of Jupiter from December 8, 1995 until Sept. 21, 2003. [Best Jupiter Missions of All Time]
In 2013, the U.S. National Research Council's Planetary Science Decadal Review issued its 10-year recommendation for NASA's planetary exploration program. Exploration of Europa was ranked as the highest-priority mission. Since then, NASA has been working toward a mission to Jupiter's icy moon.
Bright scars on a darker surface testify to a long history of impacts on Jupiter's moon Callisto in this image of Callisto from NASA's Galileo spacecraft. Image Credit & Copyright: NASA/JPL/DLR
The scene shows the stunning diversity of Europa's surface geology. Long, linear cracks and ridges crisscross the surface, interrupted by regions of disrupted terrain where the surface ice crust has been broken up and re-frozen into new patterns. Image Credit & Copyright: NASA/JPL-Caltech/SETI Institute
Geologic evidence to date shows that Europa may have had a subsurface ocean at some time in its past.. Image Credit & Copyright: NASA/JPL/University of Arizona
The first color movie of Jupiter from NASA's Cassini spacecraft shows what it would look like to peel the entire globe of Jupiter, stretch it out on a wall into the form of a rectangular map, and watch its atmosphere evolve with time.. Image Credit & Copyright: NASA/JPL/University of Arizona
Callisto: Jupiter's Dead Moon
Callisto is not only the most heality cratered object in the solar system, but it also has the oldest landscape. Callisto is thought to be a long dead world due to the lack of geologic activity on its surface. There are no signs that the landscape has changed in 4 billion years. It is believed that any changes that have taken place in the surface have come as the results of being hit by objects rather than from geologic activity.
Discovery
Callisto is the fourth of Jupiter’s moons to be discovered by Galileo Galileion Jan. 7, 1610. The discovery, along with three other Jovian moons, was the first time a moon was discovered orbiting a planet other than Earth. Galileo’s discovery eventually led to the understanding that planets orbit the sun, instead of our solar system revolving around Earth.
Exploration of Callisto
Several spacecraft have flown by Jupiter and its moons. Pioneer 10 arrived first, in 1973, followed by Pioneer 11 in 1974. Voyager 1 and Voyager 2 returned striking photos during their flybys. The Galileo spacecraft passed as low as 162 miles (261 km) over the surfaces of the Galilean moons and produced detailed images.
Cutaway view of the possible internal structure of Callisto.Callisto's interior is shown as a relatively uniform mixture of comparable amounts of ice and rock. The surface layer of Callisto is shown as white to indicate that it may differ from the underlying ice/rock layer in a variety of ways including, for example, the percentage of rock it contains. Image Credit & Copyright: NASA/ JPL
This is New Horizons' best image of Ganymede, Jupiter's largest moon, as of February, 2007. Image Credit & Copyright: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
Discovery
Ganymede was discovered by Galileo Galilei on Jan. 7, 1610. The discovery, along with three otherJovian moons, was the first time a moon was discovered orbiting a planet other than Earth. Galileo’s discovery eventually led to the understanding that planets orbit the sun, instead of our solar system revolving around Earth. Early Chinese astronomical records also show the discovery of a moon of Jupiter, which was most likely the first observation of Ganymede.
Exploration of Ganymede
Several spacecraft have flown by Jupiter and its moons. Pioneer 10 arrived first, in 1973, followed by Pioneer 11 in 1974. Voyager 1 and Voyager 2 returned striking photos during their flybys. The Galileo spacecraft passed as low as 162 miles (261 km) over the surfaces of the Galilean moons and produced detailed images.
This picture of Ganymede, Jupiter's largest satellite, was taken by Voyager 1 on the afternoon of March 5, 1979 from a range of 253,000 kilometers. Image Credit & Copyright: NASA/JPL