have so many moons that we may not have counted them all. Would you like to know the solar system moon count as of 2010? The tally is up to 167 and counting.
There are different types of moon – satellites. The size and roundness of them vary. Most are formed near their partner planet. Some are asteroids that were captured by a planet’s gravity.
Here are some terms that are used in the moon exploration business that concerns how moons orbit their planets:
Inclination: Describes the orbital path of the satellite compared to the equatorial latitude of the planet.
Prograde: Is orbiting the planet in the way that a planet orbits the Sun while it is circling between 0 and 90 degrees compared to the planet’s equator. The vast majority of moons are prograded. They circle counter clockwise if looking down at the planet’s north pole.
Retrograde: Is orbiting the opposite direction of the way planet travels around the sun and/or has an orbital path that is more than a 90 degree angle than the equator. Most, if not all retrograde moons are captured asteroids.
Irregular: Moons that have elliptical orbits and are still within the 90 degree equatorial angle.
Regular: moons are all prograde, but not all prograde moons are regular. Some are irregular.
All prograde – irregular moons have an “a” at the end of their names. All retrograde moons have names that end in the letter “e”.
In this section, we will look at some of the more interesting moons, which include our own.
We see our moon at night – sometimes even by day. It is big, round and looks a little beat up. The colors are whitish gray, gray and some black. It can also be yellow when close to the horizon and very bright and white when high in the sky.
Our Moon had different names during ancient times when many thought of it as a goddess. Some of the given names were: Diana, Lunea, Cynthia, and Selene. It has been both worshipped and feared. It was an object representing romance. It was a light for harvesting at night. It was thought of as a factor in transforming people into werewolves. It was believed that the Moon could even cause people to become “lunatics.” (Derived from the Latin word luna.)
We have only one moon. In English, we call it the Moon. It is one of many in the solar system. Here are some of additional Moon facts: It has a 2,160 mile diameter at its equator.
The Moon is a little more than one quarter the size of Earth.
Its density is about sixty percent of the density of the Earth.
Its average distance is about 221,423 miles from Earth. Its orbit is elliptical (an oval shaped path). The farthest point the Moon is from Earth is 252,667 miles.
There are tremendous temperature swings on the Moon because there is a very slight atmosphere to hold or release heat and cold.
The Moon travels around the Earth at a rate of nearly 1.5 miles per second!
There is water ice on the Moon.
Evolutionists age the Moon at 4.4 billion years.
It has 17% percent of earth’s gravity.
Have you ever noticed that there can be a “halo” around the Moon? It is not what it seems to be and neither is it where it seems to be. The circle is caused by ice crystals high in our sky.
Another phenomenon is known as the “Moon Illusion.” No one is quite sure why, but the Moon looks much bigger when seen at the horizon level.
The Moon has structure. The center, or core, is thought to be solid but could be partly molten. Moonquakes have been detected. They are very weak, leading to the belief that there might be some liquid towards the middle of the core. Moonquakes seem to be related to the tidal forces caused by interacting with Earth’s gravitational forces.
The surface temperature averages 107 degrees Celsius in the sunlight and -135 degrees Celsius in the shadows. Sometimes the temperature drops as low as -249 degrees Celsius, which would rival temperatures found in the Kuiper belt.
Galileo thought that the dark areas on the Moon were oceans. He called them maria, (plural), or mare, (singular). The mare is actually basalt rock lava beds that have cooled from the pouring out of magma, were caused by meteorite impacts cracking the surface. The largest mare is the Mare Imbrium, 1,700 miles across.
The highest areas on the moon are known as “The Highlands” and are some of the oldest surfaces on our Moon formed, during the period of volcanism. As the Moon cooled, there were flows of volcanic basalt, which were most active between 3.2 and 1.2 billion years ago. Igneous (volcanic), rock areas covers almost 80% of the Moon’s surface. Some smaller features exhibit geographical features that appear to be caused by out – gassing. (An explosive leakage from subsurface gas pockets.)
Virtually all of the Moon’s mountains are walls of craters. Very few high hills or mountains are from volcanic episodes, since the Moon has no tectonic plates; no mountains were caused by plate movement.
The Moon is mostly covered with silicon dioxide, magnesium, calcium, glass and dust, which form a layer called the lunar regolith, ranging in depth from 5 to 50 feet. It is created by the smashing of the surface that result in debris from the impacts of meteorites and micrometeorites being strewn over the surface. When brought back to earth and studied, scientists said it had the scent of gunpowder.
The crust is made of 45% oxygen, 21% silicon, 6% magnesium, 13% iron, 8% calcium and 7% aluminum. The mantle: underneath is made up of olivine, orthopyroxen and clinopyroxen. The core of the Moon is only 255 miles in diameter and seems to be made of partly molten iron and nickel. Some of the basalts on the surface also contain titanium.
The Moon is the second least dense moon in the solar system. (Only Io is less dense.) The Moon has a magnetic field that is much less potent than the one form emanating from Earth.
The moon looks a little beat up! In a way it is just that. It has small craters called craterlets, larger craters, some extremely large craters more than a hundred miles across, called “walled plains”. Most of these craters were the result of meteor hits. The larger pieces of material ejected by these collisions caused more craters to be formed. Smaller particles blasted out, called “rays”, formed patterns that stretch out for hundreds of kilometers.
The far side of the moon looks far different from that facing the earth. It does not have large maria, but it does have craters and highlands.
The Moon, (La “Luna” in Spanish), is being hit constantly by space debris. With no atmosphere to protect it, the surface is bombarded by large as well as sand-sized rocks, small meteors called “micrometeorites” they hit the moon at speeds up to 70,000 miles per hour. This makes the moon’s surface a very dangerous place for humans. A small grain could go right through the body of an exploring astronaut!
The micrometeorites affect changes on the surface of the moon: they can cause erosion. However, they are 10,000 times less effective in creating changes than those caused by air and water on the surface of our Earth.
Several years ago a military satellite turning toward the Moon to adjust its instruments, reported back an amazing find: water ice on the Moon! NASA sent a probe, called a “Lunar Prospector”, to investigate and to confirm the findings. It is now thought that ice could have come from comets that have collided with the Moon. The spacecraft Clementine has further confirmed these phenomena. The Indian probe, Chandrayaan, detected large quantities of ice.
The ice is not only in permanently shadowed craters, but it may also be found in the regolith. It seems there are literally millions of tons of ice present. One 10th of 1% of the regolith soil may be frozen water. Scientists looked again at the collected Moon rocks brought to earth by the Apollo 15 astronauts and found that there was water in some of them.
This ice could be used to support a space station on the Moon. The hydrogen and oxygen can be separated, and the elements used for drinking water, breathable air and rocket fuel.
The Moon’s atmosphere is extremely thin but has a very complicated composition. It most likely results from decay and out – gassing. These elements are: sodium, potassium, polonium, argon, oxygen, methane, nitrogen, carbon monoxide and carbon dioxide.
We have sent many “visitors” to our moon, including machine probes and manned vehicles. Later in this book, we will study these explorations.
There have been several recent discoveries, most of which were found by the lunar astronauts who brought back moon rocks. The rocks range in age from 3.1 billion years to 4.4 billion years. The rocks also reveal another important fact: The Moon has a different geologic make up than present day Earth.
The Moon has several measurable effects on Earth. One is that of the lunar eclipse. That’s when the Moon passes between the Sun and the Earth. The shadow of the Moon falls upon the Earth. From Earth, the Sun and Moon look the same size because the Moon blots out the sunlight when aligned with us.
A major Moon influence on Earth is the tidal effect. The Moon’s gravity actually pulls at our oceans. The powerful pull of our natural satellite can change the depth of the coastal waters by many feet in a few hours. (This subject is covered in the Planets / Earth section.)
Where did the Moon come from? How did it form?
There are several theories:
The Fission Hypothesis: The Moon was formed by a chunk of partly molten earth flying off into space and leaving the Pacific Ocean area as a scar.
Capture Hypothesis: The Moon was a free – wandering space object that was capture by our planet’s gravity.
Co-formation Hypothesis: The earth and Moon formed at the same time.
Giant Impact Hypothesis: A large object, perhaps a large as 1/3 of the earth, collided with our very young planet and debris was thrown into space. This debris coalesced into the Moon. This is presently, the most popular scientific theory.
Where is the Moon going? It is currently drifting away from Earth at 1 ½ inches, per year. Theoretically, over billions of years, the Moon could become a planet. But the Moon and Earth, according to science timelines, would already be destroyed by the Sun.
Did you know?
When seen on Earth, the Moon is 25,000 times brighter than the nearest star, other than our Sun. But it only reflects 11% of the sunlight shown on it.
The Moon has a synchronized rotation. A moon day rotation equals the same amount of time it takes the Moon to go around the Earth (27.3 days). Therefore, we can only see one side of the Moon at any given time.
This, the largest moon in our solar system, is also the seventh largest world as well. Titan was discovered in 1655 by Christiaan Huygens. It is the most complicated moon when considering its atmosphere and its interactions within the moon’s surface.
Larger than Pluto and Mercury, Titan is one of the 22 moons of Saturn. It is famous not only for its size but also for its atmosphere. Titan is the only moon with a substantial atmosphere. Other than our own Moon, it is now one of the most studied moons in the solar system. The largest moon in the Saturn system, it orbits Saturn from a distance of about 720,000 miles. It takes 16 earth days to circle Saturn.
Its atmosphere contains 95% nitrogen and 5% methane, plus a multitude of trace gases. Its surface air pressure is actually 50% stronger than that of Earth’s atmosphere. However, differences between temperatures of Titan and Earth are extreme. The average temperature of Titan is -292 Fahrenheit. Methane freezes just a few degrees below that level. Methane, on Titan, is found in frozen, gaseous and solid states. The atmosphere averages 190 miles in thickness. There are continuous strong winds in the upper atmosphere that are as fast as category 3 hurricanes. These winds make the atmosphere move around Titan five times faster than the spin of the moon itself. Its lower atmosphere tends to be calm.
It rains ethane on Titan, in very large drops (1cm). The rain drops to the ground, just like it does on earth. But because there is much less gravity, it can take as much as an hour for them to finally land. Most of the drops evaporate before they reach the ground.
From a distance one cannot see any features on Titan. It is covered with a yellowish brown -thick- haze of methane, ethane, and acetylene compounds. It actually snows on this moon! The snowflakes are made of methane and fall slowly to the ground, due to the light gravity of this world. Every day appears to be gloomy on Titan.
The sky is brown and the sunlight gives little more illumination than our moonlight provides. A day on Titan is 16 Earth days long. Eight are dark and, the rest are gloomily lit.
Did you know?
During the recent fly – by of Titan, by the space probe Cassini, it recorded radar images of lakes! They are filled with liquid hydrocarbons. This makes Titan the only place, other than Earth, that is known to have liquid lakes! Many of the lakes look like they may be filled in impact craters or are a result of volcanism. Others look like a typical filled – in lake on earth. Does this mean there is an equivalent to Earth’s water cycle working on Titan? Time will tell. Saturn takes 29 years to orbit the sun. As observations continue, we will be able to tell whether there is seasonality to these liquid deposits.
Iapetus is the third largest moon in the Saturn system. It is a peculiar world that is very bright on one side, very dark on the other. (One side is ten times brighter than the other side).
Iapetus is the third largest moon that orbits Saturn. It orbits at a distance of about 2.1 million miles from the planet. It takes 79.33 days to complete one orbit.
The light side looks like a typical cratered moon. The other side is as dark as charcoal and has virtually no features. The darkness may have to do with collecting dust from the moon Phoebe or maybe that part of the moon is more exposed to the sun and the ice has melted. The Cassini space probe arrived in 2004 tried to investigate why this situation exists. So far, there are no conclusions. Iapetus has polar water ice. It also has frozen carbon dioxide lying on its surface. This moon is a little less than half the size of our Moon.
Iapetus has a clearly defined equator and is marked by a mountain line around the middle. From a distance, this feature gives the moon a glued together look.
There are other moons that orbit Saturn. Mimas looks like a typical battered moon. Mimas, Rheas, Enceladus, Dione, and Tethys are midsized moons. These worlds, as well as the smaller moons, are airless and icy .
Ariel is nearly all ice. Not only is the surface icy, but so is the interior. It has strange canyons in several areas. Probably it was partially melted in its early years. This moon is about one third the size of our own.
Triton, a moon of Neptune, is a very cold place that averages – 400 Fahrenheit during the day or night. The surface water ice is as hard as granite. There may be liquid nitrogen pools lying below the surface. This type of “ground water” is heated by decaying, radioactive particles and tidal forces from nearby Neptune.
Occasionally the liquid breaks through, and geysers shoot it above the surface. As it falls, it freezes and forms snow on the surface. Methane mixed with liquid falls nearby, leaving purple and black stains near the vents. In essence these vents act as ice volcanoes.
Triton has an interesting and fairly unique feature; it has wind. The air is thin and clear. Sometimes a thin cloud can be seen. The atmosphere is fed by geysers.
Did you know?
There is a theory that a planet near Triton was once orbiting the Sun and was captured by Neptune’s gravity. One reason for this theory is that Triton orbits around Neptune in the opposite direction of the planet’s spin. (Saturn has one moon which does this and Jupiter has four.).
This is a world that is so different from the rest of the solar moons. It is a moon of constant change. A violent place, it has extraordinary events happening daily.
Io is the 13th largest space object in the solar system. Discovered by Galileo 63 Galilei, it is close to 30% the size of earth. It flies around Jupiter, making one orbit every 1.8 days! It circles Jupiter at a distance of a little more than 250,000 miles.
When Voyager 1 passed Jupiter in 1979, the cameras turned to it and captured one of the most stunning images ever taken. It was a moon with not one visible meteor crater. The place is orange, yellow, white and brown with touches of black. Some say it looks more like a giant pizza.
After several days of investigation the team of scientist realized they were looking at a moon with many active volcanoes. There are at least 300 hundred of them. These were the first active volcanoes ever seen outside of Earth. It has incredible volcanic lava temperatures that range from 1,400 to 1,700 degrees Fahrenheit. Most likely the magma contains a lot of magnesium, which tends to burn hot. The lava on Io is hotter than the lava on Earth. The vents shoot out both liquid rock and gaseous sulfur. Jets of gas and molten rock spout up as much as two hundred miles above the surface. There are even lakes of liquid sulfur and rivers of molten lava. This moon is the second hottest place in the solar system, second only to the Sun.
Most of Io’s interior is molten. The surface is a weak, brittle and has a thin crust over a hot ball of molten sulfur dioxide. No other moon is like this one. In fact, no other moon even comes close. The gravitational forces of Jupiter and three other moons pull and mix Io into this weird state and make the moon have an elliptical orbit. It is estimated that the side of Io that faces Jupiter can be pulled out into space for as far as 6 miles.
The volcanic activity is so widespread and constant that it is useless to try to map this moon, in 5 to 7 years the whole surface may look different. Every billion or so years the whole moon turns itself completely inside out!
Where the volcanoes are not spewing, there is ice and cold rock. The average temperature on Io’s surface, away from the vents, is -143 degrees Fahrenheit. Magma and ice; Io is a moon of contradictions.
Ice and cold are not the only interesting observation one can make about this world. When pictures of this moon were studied it was easy to compare the surface of Europa with glaciers on our own planet. The folds, crevasses and undulations look the same. It has 70% sunshine reflectivity off the icy surface, making it very visible in the sky. (Remember, our Moon has only 11% reflectivity.).
It’s about 2,000 miles in diameter and orbits Jupiter from a distance of 400,000 miles. Europa takes only 3.6 earth days to orbit its planet.
The icy surface area is estimated to be, on average, 30 million years old. There are some craters, grooves and cracks on its’ surface. The average temperature at the equator is – 260 degrees Fahrenheit. At the poles, the temperature drops to -370 degrees. This was caused by the underlying liquid and possibly tidal forces when it passes near other moons.
There is a very slight atmosphere around Europa. The air is composed of oxygen. When charged particles from the sun hits the surface interacts with water molecules, thereby releasing some oxygen and hydrogen occurs. The hydrogen is lighter and therefore escapes more easily from the moon’s grip.
But what is under all that ice? To quote a line from the movie 2010 it might be: “Something wonderful.” The ice is anywhere from 10 to 100 miles thick. It replenishes itself on a continuing basis. In many ways it acts like our atmosphere; it retains heat, provides protection from cosmic projectiles and blocks out dangerous rays from penetrating the outside, protective layer.
Beneath this ice cover is a sea up to 60 miles deep. It is made up of water. The core is hot rock. Could there be life in this sea? The answer is absolutely… yes! The icy surface on Europa could very well have been liquid when Jupiter and Europa were young. Primeval life may have formed in its oceans and may still be there, under the ice. This likely would be aquatic life with no knowledge of the Universe above the ice, which is not much different from the deep sea life that never breaks the surface of our own oceans. It very well could be that our first alien contact will be with creatures living on a moon circling Jupiter. Today, there may be alien life form near a hot vent of the ore, feeding and may be able to think: “What’s up there?”
There are plans to launch a spacecraft to with lasers and radars to study its’ surface. This would provide additional information about subsurface conditions. It is the next step towards having a probe land on the moon and drill, or melt, the ice in order to see if organisms dwell below the surface.
Ganymede, the largest of Jupiter’s moons and the largest moon in the Solar System, bigger than Mercury, is pocked by many impacts. The moon is mostly composed of ice, with dust and dirt lying about on its surface. The Moon’s has a skin of dirty ice and when objects hit it, they expose a clean ice sheet beneath. The materials from the collisions are thrown out onto the surrounding area, providing some contrast between clean ice and the dirty ice surface. There are many craters on the moon, suggesting that its surface is very old. The ice, over time, reduces the craters by relaxing the walls leaving more rounded edges and eventually flattened – circular scars on the surface. These are called palimpsets.
Ganymede had internal heat at some point. How much is not clear, but there can been seen some effects on the ice. This may be the reason that it has its own magnetic field.
Like Europa, it too probably might have a below – surface, saltwater sea. But the ice on this moon is much thicker than that found on Europa. The core seems to be made of metals and rock.
The outermost of the Galilean, (Jupiter’s) moons, Callisto has been peppered with debris. It is one of the more cratered worlds in our solar system. It is covered in water and carbon dioxide ice. This probably means that its surface and the object itself are very old. The relaxing of crater walls has occurred, as happened on Ganymede.
Our Moon and Callisto resemble each other but with a major difference; Callisto is mostly of water! They have the same strength in gravity and have no atmospheres, but a rock sampling from Callisto would melt at room temperature. The moon consists of a mixture of water ice and dirt. The ice thickness of the moon is several miles deeper than on Europa or Ganymede, making the possible liquid water below the crust impossible to reach.
The surface temperature on Callisto is around -230 Fahrenheit. It is the second largest moon of Jupiter and the 12th largest space object in the solar system. It orbits Jupiter from a distance of 1.2 million miles and completes one orbit of Jupiter in a little over 16.5 earth days. The core is most likely rock, the rest perhaps water ice, slush and liquid salt water.
This moon of Saturn has an orbit distance of 7.5 million miles. The 9th largest moon in Saturn’s system, it is a captured asteroid that has a retrograde orbit. One trip around Saturn takes 550 earth days. This asteroid turned- moon is pockmarked by craters. It has a water and carbon dioxide – ice, covering.
Enceladus is the most reflective of all the moons. About 99% of the sunlight reflects from its surface. It is also the smallest moon with an atmosphere. It has water geysers that provide the inconsistent atmosphere and replenishes a smooth looking surface. The energy producing these actions could be tidal in nature coming from Saturn and a few nearby moons.
The average surface temperature is – 330 degrees Fahrenheit. There are less than 20 smaller craters to be found on the moon.