In our solar system, there are nearly 200 moons orbiting eight different planets. Of course, these moons aren’t split evenly. Mercury and Venus don’t have any moons, while Jupiter has over 70—and counting. With this many moons, it’s easy to pick favorites. So I did! Here are six of my favorite moons in the solar system.
Our moon
Left: From Bill Ingalls. Top Right: Apollo 8’s iconic Earthrise, taken by Bill Anders. Bottom Right: The moon, as viewed from Earth, with Venus to the left. From Bill Dunford. Source: NASA
Naturally, I have to start with our moon, sometimes called Luna. Our Moon has a radius of 1080 miles (1737.5 kilometers) and is 238,855 miles (384,400 kilometers) from the Earth. With roughly the same apparent size as the Sun, the moon is the brightest object in our night sky. The Moon is tidally locked with the Earth, meaning we always see the same side of the Moon. The side we don’t see is often called “the dark side of the Moon,” but this is simply not true. This side of the Moon is lit by the Sun just as often as the other side.
The Moon is the only place outside of the Earth that humans have been. Thanks to this, we know tons about the Moon. For example, we know that the Moon has no atmosphere, and therefore, no wind. In addition, we have a pretty good map of the Moon and its craters. These craters are the most prominent features on the Moon’s surface.
Mimas
Left: Taken by the Cassini spacecraft. Top Right: Saturn with Mimas, a tiny dot to the bottom left of the image. Taken by the Cassini spacecraft. Bottom Right: Taken by Voyager 1. Source: NASA/JPL
Mimas just might be my favorite moon in the solar system. Discovered orbiting Saturn by William Herschel in 1789, it’s most prominent feature is the giant crater (complete with a central peak) on the right side of the image. This crater is named Herschel, after, of course, the man who discovered the moon. In the 1980s, NASA got its first up-close images of the moon as the Voyager crafts passed by. Immediately, many Star Wars fans noticed that Mimas looks an awful lot like the Death Star! Years later, the Cassini spacecraft took more fantastic images of the moon.
Mimas is one of Saturn’s closer moons, orbiting only 115,000 miles (186,000 kilometers) from the planet. Like our moon, Mimas is tidally locked with Saturn. Mimas is slightly ovoid (meaning a little more oval than a sphere, like an egg) and has a mean radius of 123 miles (198 kilometers). In addition, Mimas seems to be made entirely of water ice.
Io
Top Left: An eruption can be seen as a blue haze on top of the planet. Taken by the Galileo spacecraft. Bottom Left: A tiny Io is dwarfed by Jupiter. Right: Io, in true color. Source: NASA/JPL/University of Arizona
In 1610, Galileo pointed his telescope towards Jupiter and noticed four little dots moving back and forth across the planet. These four dots are now known as the Galilean Moons, my favorite of which is Io. Only a little larger than our moon, Io shoots around Jupiter in less than two Earth days at a distance of 262,000 miles (422,000 kilometers). As Io speeds around Jupiter and through its electric field, the moon generates a current that sparks lightning in the planet’s upper atmosphere.
Io’s weird, dotted color (making it look a little like a moldy pizza) is due to the volcanoes that cover the moon. In fact, Io is the most volcanically active body in the solar system. Like Mimas and our moon, Io is tidally locked with Jupiter. This, along with its highly elliptical orbit, cause insane tidal forces on the moon. These forces heat up Io, causing all the volcanic activity. Io seems to be made of mostly sulfur or silicate rock. These materials would explain Io’s “moldy pizza” appearance.
Phobos and Deimos
Top Left: Phobos. Bottom Left: Deimos. Right: Mars with the two moons as seen by Curiosity. Source: NASA/JPL-Caltech/GSFC/Univ. of Arizona
Deimos and Phobos were discovered by Asaph Hall in 1877. These cratered, irregularly shaped moons are among the smallest in the solar system. Right now, it’s believed that these moons are captured asteroids, but it’s possible that this is untrue. Like many other moons, these are tidally locked with Mars.
Phobos, the larger of the two, speeds around Mars three times a day. This moon is gradually moving closer to the planet, meaning that in the future, it will either crash into Mars or break apart into rings. A prominent feature of Phobos is the giant impact crater, called Stickney. Stickney is 6 miles (9.7 kilometers) wide.
Deimos only orbits Mars once every 30 hours. Deimos appears to be so tiny that it’s gravitational pull can’t hold onto ejected material after a meteorite strikes.
Titan
Left: The first image of Titan’s surface, taken by the ESA’s Huygens probe. Top Right: Titan and Diane (another of Saturn’s moons) in front of the Planet. Taken by Cassini. Bottom Right: Titan in front of Tethys (another of Saturn’s moons). Taken by Cassini. Source: NASA/JPL/ESA/University of Arizona
Titan has a radius of 1,600 miles (2,575 kilometers) and orbits Saturn once every 16 Earth days. Titan is Saturn’s largest moon, and the only moon known to have a significant atmosphere. This atmosphere, made of nitrogen, gives Titan it’s hazy appearance. Titan rains methane and ethane onto a water ice crust. Seas, lakes, and rivers, also made of methane and ethane, flow across the surface. Beneath the crust is a sea of water.
Titan’s water interior could hold life. Even more exciting, however, is the possibility of the surface holding life. Life that formed on Titan’s surface would be chemically different from our own. That being said, there is currently no evidence of Titan containing life; more research is needed.
Europa
Top Left: Taken by the Galileo spacecraft. Bottom Left: Europa’s scratched surface, taken by the Galileo spacecraft. Right: Jupiter with Europa to the right, casting a shadow on the planet. Source NASA/JPL-Caltech/SETI Institute/ASU
Europa, another Galilean moon, is largely considered to be the best shot at life off of Earth. Europa has a diameter of 1,940 miles (3,100 kilometers) and orbits Jupiter twice every seven Earth days. Europa’s surface is made of water ice with a deep liquid water ocean underneath. This icy surface is covered with scratches and cracks due to tidal forces from Jupiter, Io, and Ganymede. These tidal forces also heat up Europa’s subsurface sea.
Like Io, Europa also has an induced magnetic field from Jupiter’s magnetic field. The fact that there is a magnetic field suggests a salt water ocean under the icy surface. We know that life could potentially form there because life has formed in similar conditions on Earth. Right now, missions are being planned by NASA and the ESA (European Space Agency) to find life on Europa.
All the data in the article came from NASA.
madison brewer 