By Dr. Gary L. Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
This is the final article in a seven-part series reviewing the extraterrestrial planets and other bodies of the solar system, as well as exploratory missions to study them.
The moons of Jupiter and Saturn are home to some of the most phenomena in the solar system. Almost 150 moons have been cataloged between these two gas giants, and it’s a virtual certainty that there are still more to be discovered. Yet, among the moons that we’ve discovered so far, there are already many mysteries and intriguing features. Europa and Titan are two of the most interesting moons because of what we know about them thus far, and what future space exploration of them might reveal.
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Europa Was the Smallest Moon Galileo Discovered
In the Jovian system, few moons are more interesting than Europa, which was discovered by the astronomer Galileo by telescope in 1610. Although it was the smallest of the moons that Galileo identified, it is still the sixth-largest moon of all 181 moons currently cataloged in the entire solar system.
Europa has been visited and studied by a number of NASA spacecraft including Pioneer 10 and 11 in 1973 and 1974, by Voyager 1 and 2 in 1979, by the Galileo probe that operated between 1995 and 2003, and by the New Horizons probe, which swung through the Jovian system in 2007 for a gravity assist on its way to the Kuiper Belt.
Europa is actually the smoothest celestial body known in the solar system. It features no significant mountain ridges or craters. It is also one of the brightest surfaces in terms of albedo (i.e. reflectivity). Scientists believe this is most likely because Europa’s surface is young and tectonically active. Experts estimate that, while Europa is as old as its host planet (about 4.5 billion years old), its surface is only about 180 to 200 million years in age.
It is also interesting that radiation on the surface of Europa is strong enough to kill a human being in as little as one day’s worth of exposure. This is due to the intense solar radiation and energetic particles trapped by Jupiter’s magnetic field.
The most intriguing feature of Europa by far is that scientists believe there is a liquid saltwater ocean about 100 km (62 miles) beneath the surface of the moon. Experts hypothesize that Europa’s core is heated by the constant torsion of tidal forces from Jupiter’s pull. This heat in turn melts the subsurface ice and creates an underground sea.
If this theory is confirmed, it would be exciting because everywhere we find water on Earth — even in the deepest, darkest, coldest trenches of the oceans — we find some form of life. So if a subsurface ocean does exist on Europa, it might be the most plausible place to look for extraterrestrial life in the solar system. Future missions are being planned to explore this possibility.
Titan, the Second Largest Moon in the Solar System
In the Saturnian system, Titan stands apart of all of Saturn’s moons. In addition to being Saturn’s largest moon, Titan is also the second-largest moon in the solar system, bested only by Ganymede of Jupiter. It was discovered by Dutch physicist Christiaan Huygens in 1655.
Most of what we know about Titan we learned from the Voyager 2 probe, which passed through in 1980, and the Cassini probe, which arrived at Saturn in 2004. Cassini flew by Titan 127 times until its planned de-orbiting in 2017. In addition to flybys, Cassini also dropped the Huygens lander to the surface of Titan. Following the successful landing via parachute, Huygens took high-resolution photographs and collected other data.
Titan has a hazy orange atmosphere composed mainly of 95 percent nitrogen and five percent methane. One of the most unusual features of Titan is that it is the only celestial body in the solar system, apart from Earth, to have liquid running and pooling on its surface. However, Titan’s lakes are not composed of water, but rather of liquid methane and ethane. Titan also features methane rain, with rivers that ebb and flow throughout its surface.
Like Jupiter’s moon Europa, some scientists also believe that Titan could have a subsurface ocean composed of water and ammonia. Organic compounds have been detected on Titan. So it is believed that if Titan were the same distance from the Sun as Earth, its environment would be very similar to our own. In fact, if our Sun becomes a Red Giant near the end of its life as expected (about 6 billion years from now) and if it expands to warm the outer solar system, that environmental change might actually happen.
Finally, Titan has served as a model for what have been called “cloudy bodies.” Scientists study Titan to extrapolate to exoplanets with thick atmospheres that have been discovered outside the solar system.
Both Europa and Titan have extremely interesting features worthy of further inquiry and exploration. Hopefully, future NASA budgets will allow for us to return to these bodies and study them in greater detail.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.