*2.1.1 Mercury*

Mercury is the planet closest to the Sun, the smallest of the Solar System planets, and similar in size to Earth's moon. It has no moons, and has a cratered surface that is similar to the topography of Earth's moon. Given its proximity to the Sun and high temperature, Mercury's atmosphere is thin with a constituent number density ≤ 1011 particles/m3 [15]. Mercury's limited atmosphere consists of oxygen, sodium, potassium, and calcium that evolved from surface material. Thermal effects that increase the temperature of the crust and the impact of solar particles and meteorites on the surface create this atmospheric composition. Limited atmospheric hydrogen and helium are derived from particles emitted by the Sun, and


*a Adapted from Refs. [1, 15]. Rounded to two significant figures due to various values quoted in the literature. b Ref. [28].*

#### **Table 1.**

*General Solar System Planet Characteristics.a,b*

**Figure 1.** *Solar System planets and the dwarf planet Pluto [35].*


*b The number of moons is derived from Ref. [28].*

#### **Table 2.**

*Solar System Planetary Data.a,b*

trapped by Mercury's weak magnetic field. The existence of this field suggests that Mercury has an iron core, and that a portion of it is a rotating liquid [22].

Additional Mercury data has been developed by a number of Solar System probes [11] including Mariner 10 and Messenger. The Japanese probe BepiColombo will provide additional data.

#### *2.1.2 Venus*

The second planet from the Sun is Venus, and it is somewhat smaller than Earth. In spite of the fact that Venus is the closest planet to the Earth, it is one of the least explored planets in the Solar System. Venus is similar in size and mass to the Earth, but these two planets are very different in their environment including temperatures, surface features, and atmospheric composition. Its thick atmosphere traps

**7**

surface.

*2.1.4 Mars*

*Solar System Planets and Exoplanets*

these preliminary observations.

Earth's [22].

*2.1.3 Earth*

*DOI: http://dx.doi.org/10.5772/intechopen.98431*

heat making Venus the hottest planet in the Solar System. Venus has an atmosphere composed of about 97% carbon dioxide with about 3% nitrogen. Trace amounts of water, carbon monoxide, argon, and sulfur dioxide comprise most of the remaining composition. The surface atmospheric pressure is about 90 times that of Earth [15]. Venus also appears to be have been affected by significant surface volcanic activity. Mariner 2 measured a surface temperature greater than 750 K [7, 15]. Sulfuric acid clouds are predicted by limited probe data [7]. Venus also differs from Earth with a slow retrograde rotation rate of about 240 days and lack of a magnetic field that that is an essential element in shielding a planet from the effects of the Solar wind. In addition, Venus has no moon, and its magnetic field is significantly weaker than

The possible detection of phosphine in the Venusian atmosphere created interest in further exploration of this planet [21]. Phosphine is an uncommon molecular species that is associated with anerobic bacteria. Its detection raised the possibility of extraterrestrial life. However, further measurements are required to confirm

Venus appears to be bright because its heavy cloud cover reflects most of the incident sunlight. Astronomers have been able to cut through the clouds of Venus with radar, because radio waves pass through the clouds and bounce off the surface. Using radar, the NASA probe Magellan assembled a detailed surface map while in orbit around Venus [7]. These radar images suggest that Venus has continents with varied topography including canyons, meteorite craters, and volcanic mountains [11].

Excluding the possible phosphine detection on Venus, Earth is the only Solar System planet that has sustained life. In addition, Earth is the only planet with liquid water residing on its surface, and is the largest of the terrestrial planets. Its surface is composed of about 29% land and 71% water that include oceans, lakes,

Earth is protected from charged particle ionizing radiation emitted by Solar flares and other disturbances [4–6, 14, 15] by its geomagnetic field and atmosphere. Charged particles from Solar Particle Events and Galactic Cosmic Radiation are reduced in intensity by the attenuating properties of the atmosphere and the action of the geomagnetic field. The atmosphere also shields Earth from a portion of the Sun's ultraviolet radiation that mitigates its harmful effects. Earth's atmosphere is composed of 78% nitrogen, 21% oxygen, and about 1% argon. Trace gases accounting for about 0.1% of the atmospheric composition includes carbon dioxide,

Earth rotates in a prograde manner with a period of 24 hours. It has a nearly circular orbit with a mean distance from the Sun of 1 AU. Given the current Solar luminosity, this distance creates a positive environment for sustaining liquid water

The Earth has varied topography that is not static and still experiences periodic volcanic eruptions. Earthquakes and violent weather continue to reshape the Earth's

Mars is about 50% further from the Sun than Earth and about half the Earth's size. The planet Mars is only about 10% as massive as the Earth, and has two small moons [7, 10, 11, 15, 28]. Its distinctive reddish color is attributed to the presence of

and rivers [7, 15]. Ice covers much of Earth's Polar Regions.

that is an essential element for life to be created and sustained.

methane, nitrous oxides, and ozone [7, 15].

iron oxide in the crust and surface dust.

#### *Solar System Planets and Exoplanets DOI: http://dx.doi.org/10.5772/intechopen.98431*

heat making Venus the hottest planet in the Solar System. Venus has an atmosphere composed of about 97% carbon dioxide with about 3% nitrogen. Trace amounts of water, carbon monoxide, argon, and sulfur dioxide comprise most of the remaining composition. The surface atmospheric pressure is about 90 times that of Earth [15]. Venus also appears to be have been affected by significant surface volcanic activity. Mariner 2 measured a surface temperature greater than 750 K [7, 15]. Sulfuric acid clouds are predicted by limited probe data [7]. Venus also differs from Earth with a slow retrograde rotation rate of about 240 days and lack of a magnetic field that that is an essential element in shielding a planet from the effects of the Solar wind. In addition, Venus has no moon, and its magnetic field is significantly weaker than Earth's [22].

The possible detection of phosphine in the Venusian atmosphere created interest in further exploration of this planet [21]. Phosphine is an uncommon molecular species that is associated with anerobic bacteria. Its detection raised the possibility of extraterrestrial life. However, further measurements are required to confirm these preliminary observations.

Venus appears to be bright because its heavy cloud cover reflects most of the incident sunlight. Astronomers have been able to cut through the clouds of Venus with radar, because radio waves pass through the clouds and bounce off the surface. Using radar, the NASA probe Magellan assembled a detailed surface map while in orbit around Venus [7]. These radar images suggest that Venus has continents with varied topography including canyons, meteorite craters, and volcanic mountains [11].

### *2.1.3 Earth*

*Solar System Planets and Exoplanets*

*Solar System planets and the dwarf planet Pluto [35].*

**Mass** ( *M*<sup>⊕</sup> ) **Mean** 

**distance from Sol (AU)**

Mercury (0) 0.055 0.39 0.21 0.24 3.7 Venus (0) 0.82 0.72 0.007 0.62 8.9 Earth (1) 1.00 1.0 0.017 1.0 9.8 Mars (2) 0.11 1.5 0.093 1.9 3.7 Jupiter (79) 320 5.2 0.049 12 23 Saturn (82) 95 9.5 0.053 29 9.1 Uranus (27) 15 19 0.046 84 8.3 Neptune (14) 17 30 0.012 160 11

**Orbital eccentricity** **Orbital period (y)**

**Equatorial surface gravitational acceleration (m/s2 )**

**6**

*2.1.2 Venus*

*a*

*b*

**Table 2.**

**Figure 1.**

**Planet (Number of moons)**

will provide additional data.

*Adapted from Refs. [1, 3, 4, 10, 15].*

*Solar System Planetary Data.a,b*

*The number of moons is derived from Ref. [28].*

trapped by Mercury's weak magnetic field. The existence of this field suggests that

Additional Mercury data has been developed by a number of Solar System probes [11] including Mariner 10 and Messenger. The Japanese probe BepiColombo

The second planet from the Sun is Venus, and it is somewhat smaller than Earth. In spite of the fact that Venus is the closest planet to the Earth, it is one of the least explored planets in the Solar System. Venus is similar in size and mass to the Earth, but these two planets are very different in their environment including temperatures, surface features, and atmospheric composition. Its thick atmosphere traps

Mercury has an iron core, and that a portion of it is a rotating liquid [22].

Excluding the possible phosphine detection on Venus, Earth is the only Solar System planet that has sustained life. In addition, Earth is the only planet with liquid water residing on its surface, and is the largest of the terrestrial planets. Its surface is composed of about 29% land and 71% water that include oceans, lakes, and rivers [7, 15]. Ice covers much of Earth's Polar Regions.

Earth is protected from charged particle ionizing radiation emitted by Solar flares and other disturbances [4–6, 14, 15] by its geomagnetic field and atmosphere. Charged particles from Solar Particle Events and Galactic Cosmic Radiation are reduced in intensity by the attenuating properties of the atmosphere and the action of the geomagnetic field. The atmosphere also shields Earth from a portion of the Sun's ultraviolet radiation that mitigates its harmful effects. Earth's atmosphere is composed of 78% nitrogen, 21% oxygen, and about 1% argon. Trace gases accounting for about 0.1% of the atmospheric composition includes carbon dioxide, methane, nitrous oxides, and ozone [7, 15].

Earth rotates in a prograde manner with a period of 24 hours. It has a nearly circular orbit with a mean distance from the Sun of 1 AU. Given the current Solar luminosity, this distance creates a positive environment for sustaining liquid water that is an essential element for life to be created and sustained.

The Earth has varied topography that is not static and still experiences periodic volcanic eruptions. Earthquakes and violent weather continue to reshape the Earth's surface.

#### *2.1.4 Mars*

Mars is about 50% further from the Sun than Earth and about half the Earth's size. The planet Mars is only about 10% as massive as the Earth, and has two small moons [7, 10, 11, 15, 28]. Its distinctive reddish color is attributed to the presence of iron oxide in the crust and surface dust.

Mars' atmosphere is composed primarily of carbon dioxide (95%) and nitrogen (3%) with the remainder consisting of argon with trace amounts of carbon monoxide, methane, oxygen, water, and other gases. Mars is also subjected to dust storms that can be massive as well as severe. Its atmosphere is thin with a surface pressure that is less than 1% of sea level pressure on Earth.

Various surface temperatures are quoted in the literature but lie roughly in the range of 130–290 K [15]. The Polar Regions are considerably colder with ice and solid carbon dioxide forming the polar caps [7, 15].

Mars has a 24.5 hour prograde rotation period that is somewhat larger than Earth's. The surface includes cratered areas, extinct volcanoes, chasms, and areas suggesting the previous existence of the action of water flow. In its past Mars was probably warmer than it is today with significantly more water and a thicker atmosphere.

There are anomalies in the Martian magnetic field [22]. Most of the Northern hemisphere is unmagnitized, but portions of the Southern regions are magnetized. These anomalies suggest that at one time Mars had a magnetic field that was similar to Earth's [22].

A number of probes including NASA's Viking 1 and 2 orbiters, as well as the Hubble Space Telescope provided data regarding the characteristics of Mars. Rovers including NASA's Spirit, Opportunity, and Curiosity added additional surface data [11]. Other probes are likely to begin providing data in 2021. These include NASA's Perseverance, China's Tianwen-1, and the United Arab Emirates' Hope.

The possibility of space missions and colonization of Mars are areas of active research [18]. Considerable research is required to develop spacecraft and Mars habitats to permit these activities to occur in a safe manner. A successful colonization effort must provide food, water, power, and shelter. The space radiation environment including Solar Particle Events and Galactic Cosmic Radiation should also be addressed to ensure the health and safety of the colonists [4, 6, 14, 18].

### *2.1.5 Jupiter*

Jupiter is the largest of the outer four planets. Jupiter and Saturn are often designated gas giants while Uranus and Neptune are ice giants.

**Table 3** provides a comparison of the atmospheres of the Sun and the gas giant planets derived from Refs. [10, 15]. Jupiter and Saturn have average compositions similar to the Sun. Uranus and Neptune are also similar in composition to the Sun, but have a higher fraction of the heavier elements.


**9**

*Solar System Planets and Exoplanets*

composed of dust [15].

about 650x106

*2.1.6 Saturn*

structures.

*2.1.7 Uranus*

*DOI: http://dx.doi.org/10.5772/intechopen.98431*

[11] and has an orbital period of about 12 years.

[15]. The spot has a rotation period of about 10 hours [15].

are discussed in Section 2.2.1. Jupiter has 79 moons [28].

Juno Space Probe have added additional data [11, 15].

with an equatorial bulge [7]. Saturn's mass is about 95 times Earth's.

broad and flat, and are composed of ice chunks and rocky material [7].

core. Jupiter's field extends about 5x106

complex field structure [22].

less complex than Jupiter's field.

Observational data suggest that Jupiter and Saturn possibly have rocky cores of magnesium, silicon, and iron with additional icy mass. Numerical simulations, based on limited data [15], suggest that the cores of Jupiter and Saturn have masses of about 10 *M*⊕ and 15 *M*<sup>⊕</sup> , respectively. These values have an uncertainty of about 50% [15]. Jupiter is more than twice as massive as the combined mass of the other Solar System planets. However, its mass is about 0.001 of the Sun's mass. Jupiter is the most rapidly rotating Solar System planet with a rotational period of about 10 hours

Jupiter is the largest Solar System planet, and has a number of distinctive features. Its Giant Red Spot is a storm region that is about twice as large as the Earth

Jupiter also has very thin rings. The first of these, discovered by Voyager 1, are considerably less prominent than Saturn's [7]. The rings appear to be primarily

Galileo discovered its largest moons (Ganymede, Callisto, Europa, and Io) that

Jupiter's magnetic field is significantly stronger [15, 31] than Earth's field and has a large physical extent. It is likely generated by electrical currents in the planet's

addition, there are regions of enhanced magnetic flux near the poles that create a

The Voyager 1 probe provided an initial view of Jupiter and observed volcanic activity [11]. Pioneer 10 and 11, Voyager 2, NASA's Cassini Space Probe, and the

Saturn lies beyond Jupiter and is the sixth planet from the Sun. It has a rotational period of about 11 hours that partially explains why Saturn is an oblate spheroid

Saturn has cloud bands that are similar to those on Jupiter, but they are less colorful. Voyager 1 and 2, the Hubble Space Telescope, and the Cassini Space Mission provided views of the color variations as well as Saturn's ring

**Table 3** lists the elemental compositions of the atmosphere of Saturn. The atmospheric molecular gases include hydrogen, helium, methane, and ammonia. Saturn has a complex ring system and the largest number of moons (82) of any planet in the Solar System [28]. The Hubble Space Telescope imaged Saturn and provided a unique view of its rings. NASA's Cassini Space Probe provided a detailed view of the rings that indicated their structure was comprised of numerous narrow ringlets [11]. Voyager 1 and 2 obtained additional data. The rings are generally

Saturn's magnetic field is almost symmetric about its axis [22]. It is weaker and

Uranus is the Solar System planet with the third largest diameter [15]. It has an atmosphere dominated by hydrogen, helium, and methane. Ammonia and trace amounts of water and hydrogen sulfide are also present [7, 10, 15]. Although Voyager 2 and the Hubble Space Telescope observed some cloud bands, these are

km behind the planet extending beyond the orbit of Saturn [7]. In

km in front of the planet and stretches

#### **Table 3.**

*Composition of Giant Planet Atmospheres.a*

#### *Solar System Planets and Exoplanets DOI: http://dx.doi.org/10.5772/intechopen.98431*

*Solar System Planets and Exoplanets*

atmosphere.

to Earth's [22].

*2.1.5 Jupiter*

that is less than 1% of sea level pressure on Earth.

solid carbon dioxide forming the polar caps [7, 15].

Mars' atmosphere is composed primarily of carbon dioxide (95%) and nitrogen (3%) with the remainder consisting of argon with trace amounts of carbon monoxide, methane, oxygen, water, and other gases. Mars is also subjected to dust storms that can be massive as well as severe. Its atmosphere is thin with a surface pressure

Various surface temperatures are quoted in the literature but lie roughly in the range of 130–290 K [15]. The Polar Regions are considerably colder with ice and

Mars has a 24.5 hour prograde rotation period that is somewhat larger than Earth's. The surface includes cratered areas, extinct volcanoes, chasms, and areas suggesting the previous existence of the action of water flow. In its past Mars was probably warmer than it is today with significantly more water and a thicker

There are anomalies in the Martian magnetic field [22]. Most of the Northern hemisphere is unmagnitized, but portions of the Southern regions are magnetized. These anomalies suggest that at one time Mars had a magnetic field that was similar

A number of probes including NASA's Viking 1 and 2 orbiters, as well as the Hubble Space Telescope provided data regarding the characteristics of Mars. Rovers including NASA's Spirit, Opportunity, and Curiosity added additional surface data [11]. Other probes are likely to begin providing data in 2021. These include NASA's

The possibility of space missions and colonization of Mars are areas of active research [18]. Considerable research is required to develop spacecraft and Mars habitats to permit these activities to occur in a safe manner. A successful colonization effort must provide food, water, power, and shelter. The space radiation environment including Solar Particle Events and Galactic Cosmic Radiation should also be addressed to ensure the health and safety of the colonists [4, 6, 14, 18].

Jupiter is the largest of the outer four planets. Jupiter and Saturn are often

**Table 3** provides a comparison of the atmospheres of the Sun and the gas giant planets derived from Refs. [10, 15]. Jupiter and Saturn have average compositions similar to the Sun. Uranus and Neptune are also similar in composition to the Sun,

**Gas Atmospheric Elemental Composition (Fractional number density of particles)a**

Hydrogen H:0.84 0.86 0.96 0.85 0.85 Helium He:0.20 0.16 0.034 0.18 0.18 Water O:0.0017 0.0026 >0.0017 >0.0017 >0.0017 Methane C:0.00079 0.0021 0.0045 0.024 0.035 Ammonia N:0.00022 0.00026 0.0005 <0.00022 <0.00022

**Sun Jupiter Saturn Uranus Neptune**

S:0.000037 ~0.00022 0.0004 0.00037 0.001

designated gas giants while Uranus and Neptune are ice giants.

but have a higher fraction of the heavier elements.

Perseverance, China's Tianwen-1, and the United Arab Emirates' Hope.

**8**

*a*

**Table 3.**

Hydrogen Sulfide

*Derived from Refs. [10, 15].*

*Composition of Giant Planet Atmospheres.a*

Observational data suggest that Jupiter and Saturn possibly have rocky cores of magnesium, silicon, and iron with additional icy mass. Numerical simulations, based on limited data [15], suggest that the cores of Jupiter and Saturn have masses of about 10 *M*⊕ and 15 *M*<sup>⊕</sup> , respectively. These values have an uncertainty of about 50% [15].

Jupiter is more than twice as massive as the combined mass of the other Solar System planets. However, its mass is about 0.001 of the Sun's mass. Jupiter is the most rapidly rotating Solar System planet with a rotational period of about 10 hours [11] and has an orbital period of about 12 years.

Jupiter is the largest Solar System planet, and has a number of distinctive features. Its Giant Red Spot is a storm region that is about twice as large as the Earth [15]. The spot has a rotation period of about 10 hours [15].

Jupiter also has very thin rings. The first of these, discovered by Voyager 1, are considerably less prominent than Saturn's [7]. The rings appear to be primarily composed of dust [15].

Galileo discovered its largest moons (Ganymede, Callisto, Europa, and Io) that are discussed in Section 2.2.1. Jupiter has 79 moons [28].

Jupiter's magnetic field is significantly stronger [15, 31] than Earth's field and has a large physical extent. It is likely generated by electrical currents in the planet's core. Jupiter's field extends about 5x106 km in front of the planet and stretches about 650x106 km behind the planet extending beyond the orbit of Saturn [7]. In addition, there are regions of enhanced magnetic flux near the poles that create a complex field structure [22].

The Voyager 1 probe provided an initial view of Jupiter and observed volcanic activity [11]. Pioneer 10 and 11, Voyager 2, NASA's Cassini Space Probe, and the Juno Space Probe have added additional data [11, 15].

#### *2.1.6 Saturn*

Saturn lies beyond Jupiter and is the sixth planet from the Sun. It has a rotational period of about 11 hours that partially explains why Saturn is an oblate spheroid with an equatorial bulge [7]. Saturn's mass is about 95 times Earth's.

Saturn has cloud bands that are similar to those on Jupiter, but they are less colorful. Voyager 1 and 2, the Hubble Space Telescope, and the Cassini Space Mission provided views of the color variations as well as Saturn's ring structures.

**Table 3** lists the elemental compositions of the atmosphere of Saturn. The atmospheric molecular gases include hydrogen, helium, methane, and ammonia.

Saturn has a complex ring system and the largest number of moons (82) of any planet in the Solar System [28]. The Hubble Space Telescope imaged Saturn and provided a unique view of its rings. NASA's Cassini Space Probe provided a detailed view of the rings that indicated their structure was comprised of numerous narrow ringlets [11]. Voyager 1 and 2 obtained additional data. The rings are generally broad and flat, and are composed of ice chunks and rocky material [7].

Saturn's magnetic field is almost symmetric about its axis [22]. It is weaker and less complex than Jupiter's field.

#### *2.1.7 Uranus*

Uranus is the Solar System planet with the third largest diameter [15]. It has an atmosphere dominated by hydrogen, helium, and methane. Ammonia and trace amounts of water and hydrogen sulfide are also present [7, 10, 15]. Although Voyager 2 and the Hubble Space Telescope observed some cloud bands, these are

less distinct and colorful than those on Jupiter and Saturn. Uranus' interior generates considerably less thermal energy than Jupiter and Saturn [7].

Uranus has a distinctive orbit that differs from other Solar System planets. Its orbit is unique since the obliquity of Uranus' rotation axis is about 98 degrees. Contrary to the other Solar System planets, Uranus rotates on its side in the orbital plane [7]. The net effect of Uranus' orbital characteristics is that during its 84 year period one pole at a time receives more solar radiation than the equatorial region [7, 15]. However, measurements suggest that Uranus' equatorial region is warmer than its poles [7].

Uranus has a system of multiple rings as well as 27 moons [28]. Voyager 2 and the Hubble Space Telescope observed these ring structures. Uranus' rings are faint and much less dramatic than those on Saturn. The rings also wobble due to an unsymmetrical gravitational field since Uranus has a slightly flattened geometric structure [7].

Uranus also possesses a non-symmetric magnetic field. This field is significantly lopsided [7]. There is currently no viable explanation for this field structure.

#### *2.1.8 Neptune*

Neptune was predicted to exist following a celestial mechanics analysis of anomalies in the expected orbit of Uranus. In 1846, it was discovered near the predicted position. Neptune resides at about 30 AU from the Sun, and its orbital period is about 160 years [7, 15].

As noted in **Table 3**, Neptune has an atmosphere dominated by hydrogen and helium with a smaller amount of methane, and is similar to the atmosphere on Uranus. Voyager 2 revealed a blue color and the fastest winds in the Solar System with speeds reaching 2100 km/h [7]. The blue color is derived from small amounts of methane in its hydrogen and helium atmosphere [7].

As noted in **Table 2**, Neptune has a mass about 17 times the Earth's, and it is about four times wider than Earth [15]. In a manner similar to Jupiter and Saturn, Neptune generates more energy than it receives from the Sun [15].

In a similar manner to the other giant planets, Neptune has a system of multiple rings as well as 14 moons [28]. However, Neptune's rings are not as extensive as Saturn's. Voyager 2 observed that Neptune's rings appear to be composed of a high concentration of dust particles [7].

#### **2.2 Additional Solar System Bodies**

In addition to planets, there are additional bodies that reside in the Solar System and have the potential to affect planetary motion as well as their environment. These bodies include planetary moons, the Asteroid Belt, comets, Kuiper Belt Objects, and meteorites. Each of these Solar System bodies is addressed in subsequent discussion.

#### *2.2.1 Planetary Moons*

As noted in **Table 2**, the number of moons varies with the Solar System planet and their characteristics [1, 3, 4, 10, 15]. The larger planets tend to have more moons than the smaller ones. However, dwarf planet Pluto has five moons, which is an exception to the aforementioned trend [28, 29]. Its moon Charon is larger than any other Solar System moon relative to its planet size. **Table 4** summarizes the four largest Jupiter moons (Callisto, Io, Europa, and Ganymede), Saturn's largest moon (Titan), Neptune's largest moon (Triton), and Earth's moon that are more massive and physically larger than Charon. Characteristics of these planetary satellites including their mass, radius, density, orbital period, and semimajor axis are summarized in **Table 4**.

**11**

*Solar System Planets and Exoplanets*

**Moon (Planet) Mass** 

*2.2.1.1 Ganymede*

Ganymede (Jupiter)

Triton (Neptune)

*a*

**Table 4.**

under the surface ice [7].

*2.2.1.2 Callisto*

*2.2.1.3 Europa*

surface with numerous craters [7, 15].

*Data for Selected Solar System Moons.a*

bonds to produce hydrogen and oxygen.

*DOI: http://dx.doi.org/10.5772/intechopen.98431*

**(1022 kg)**

**Radius (103 km)**

Moon (Earth) 7.3 1.7 3.4 27 380 Io (Jupiter) 8.9 1.8 3.5 1.8 420 Europa (Jupiter) 4.8 1.6 3.0 3.6 670

Callisto (Jupiter) 11 2.4 1.8 17 1900 Titan (Saturn) 13 2.6 1.9 16 1200

*Derived from Ref. [15]. Two significant digits are used due to various literature values.*

**Density (g/cm3 )**

15 2.6 1.9 7.2 1100

2.1 1.4 2.1 5.9 350

**Orbital Period (d)**

**Semimajor Axis (103 km)**

Jupiter's moon Ganymede has a diameter of about 5200 km and is the largest moon in the Solar System. It is more massive than Pluto. Ganymede has an icy

Ref. [7] suggests that Ganymede has a structure comprised of three basic layers. The first is an iron core with the possible presence of sulfur. A layer of rock surrounds the core. The final layer is an icy crust that overlays the rocky layer.

Ganymede has an electromagnetic field that is likely generated by currents in its core. The field also has a contribution from inductive effects caused by Jupiter's magnetic field. These effects could be attributed to a layer of salt water residing

The atmosphere of Ganymede is limited and contains oxygen [7]. The oxygen arises from the interaction of sunlight on surface water molecules that break their

Callisto is another moon of Jupiter that is smaller than Ganymede, but larger than Earth's moon. The atmosphere is very thin and comprised primarily of carbon

Another of Jupiter's moons Europa is smaller than Earth's moon and has a diameter of about 3100 km. It has a grooved icy terrain with few craters [15]. The Galileo

Europa is believed to have an ocean of liquid water under its icy crust that could be about 100 km in depth. A rocky mantle forms the seabed of this ocean [7]. The

dioxide. Reference 7 suggests that Callisto is a combination of ice and rock. Callisto's icy and rocky surface is estimated to be about 100 km thick and is heavily cratered. An ocean of salty water is presumed to reside under the surface ice. The existence of the ocean is inferred from magnetic field measurements that provide a broad range of possible depths ranging from 10 to 300 km [7]. This depth variation depends on the type and concentration of materials in the water. The interior of Callisto is presumed to be rock with a density that increases with depth.

probe provided data that improved the understanding of Europa.

*Solar System Planets and Exoplanets DOI: http://dx.doi.org/10.5772/intechopen.98431*


#### **Table 4.**

*Solar System Planets and Exoplanets*

*2.1.8 Neptune*

period is about 160 years [7, 15].

concentration of dust particles [7].

**2.2 Additional Solar System Bodies**

quent discussion.

*2.2.1 Planetary Moons*

of methane in its hydrogen and helium atmosphere [7].

Neptune generates more energy than it receives from the Sun [15].

less distinct and colorful than those on Jupiter and Saturn. Uranus' interior gener-

lopsided [7]. There is currently no viable explanation for this field structure.

Neptune was predicted to exist following a celestial mechanics analysis of anomalies in the expected orbit of Uranus. In 1846, it was discovered near the predicted position. Neptune resides at about 30 AU from the Sun, and its orbital

As noted in **Table 3**, Neptune has an atmosphere dominated by hydrogen and helium with a smaller amount of methane, and is similar to the atmosphere on Uranus. Voyager 2 revealed a blue color and the fastest winds in the Solar System with speeds reaching 2100 km/h [7]. The blue color is derived from small amounts

As noted in **Table 2**, Neptune has a mass about 17 times the Earth's, and it is about four times wider than Earth [15]. In a manner similar to Jupiter and Saturn,

In a similar manner to the other giant planets, Neptune has a system of multiple rings as well as 14 moons [28]. However, Neptune's rings are not as extensive as Saturn's. Voyager 2 observed that Neptune's rings appear to be composed of a high

In addition to planets, there are additional bodies that reside in the Solar System

As noted in **Table 2**, the number of moons varies with the Solar System planet and their characteristics [1, 3, 4, 10, 15]. The larger planets tend to have more moons than the smaller ones. However, dwarf planet Pluto has five moons, which is an exception to the aforementioned trend [28, 29]. Its moon Charon is larger than any other Solar System moon relative to its planet size. **Table 4** summarizes the four largest Jupiter moons (Callisto, Io, Europa, and Ganymede), Saturn's largest moon (Titan), Neptune's largest moon (Triton), and Earth's moon that are more massive and physically larger than Charon. Characteristics of these planetary satellites including their mass, radius, density, orbital period, and semimajor axis are summarized in **Table 4**.

and have the potential to affect planetary motion as well as their environment. These bodies include planetary moons, the Asteroid Belt, comets, Kuiper Belt Objects, and meteorites. Each of these Solar System bodies is addressed in subse-

Uranus has a distinctive orbit that differs from other Solar System planets. Its orbit is unique since the obliquity of Uranus' rotation axis is about 98 degrees. Contrary to the other Solar System planets, Uranus rotates on its side in the orbital plane [7]. The net effect of Uranus' orbital characteristics is that during its 84 year period one pole at a time receives more solar radiation than the equatorial region [7, 15]. However, measurements suggest that Uranus' equatorial region is warmer than its poles [7]. Uranus has a system of multiple rings as well as 27 moons [28]. Voyager 2 and the Hubble Space Telescope observed these ring structures. Uranus' rings are faint and much less dramatic than those on Saturn. The rings also wobble due to an unsymmetrical gravitational field since Uranus has a slightly flattened geometric structure [7]. Uranus also possesses a non-symmetric magnetic field. This field is significantly

ates considerably less thermal energy than Jupiter and Saturn [7].

**10**

*Data for Selected Solar System Moons.a*

#### *2.2.1.1 Ganymede*

Jupiter's moon Ganymede has a diameter of about 5200 km and is the largest moon in the Solar System. It is more massive than Pluto. Ganymede has an icy surface with numerous craters [7, 15].

Ref. [7] suggests that Ganymede has a structure comprised of three basic layers. The first is an iron core with the possible presence of sulfur. A layer of rock surrounds the core. The final layer is an icy crust that overlays the rocky layer.

Ganymede has an electromagnetic field that is likely generated by currents in its core. The field also has a contribution from inductive effects caused by Jupiter's magnetic field. These effects could be attributed to a layer of salt water residing under the surface ice [7].

The atmosphere of Ganymede is limited and contains oxygen [7]. The oxygen arises from the interaction of sunlight on surface water molecules that break their bonds to produce hydrogen and oxygen.

#### *2.2.1.2 Callisto*

Callisto is another moon of Jupiter that is smaller than Ganymede, but larger than Earth's moon. The atmosphere is very thin and comprised primarily of carbon dioxide. Reference 7 suggests that Callisto is a combination of ice and rock.

Callisto's icy and rocky surface is estimated to be about 100 km thick and is heavily cratered. An ocean of salty water is presumed to reside under the surface ice. The existence of the ocean is inferred from magnetic field measurements that provide a broad range of possible depths ranging from 10 to 300 km [7]. This depth variation depends on the type and concentration of materials in the water. The interior of Callisto is presumed to be rock with a density that increases with depth.

#### *2.2.1.3 Europa*

Another of Jupiter's moons Europa is smaller than Earth's moon and has a diameter of about 3100 km. It has a grooved icy terrain with few craters [15]. The Galileo probe provided data that improved the understanding of Europa.

Europa is believed to have an ocean of liquid water under its icy crust that could be about 100 km in depth. A rocky mantle forms the seabed of this ocean [7]. The

existence of this ocean has caused considerable speculation regarding the presence of possible life forms. At the present time, this is merely speculation without supporting evidence.

The surface of Europa is smooth that suggests a relative young origin given the dearth of craters. Its surface is also uniquely colored with interesting patterns. Neither of these unique features has been satisfactorily explained [7].

The atmosphere of Europa is limited and contains oxygen. In a manner previously addressed in the Ganymede discussion, oxygen is liberated from the interaction of sunlight on surface water molecules.

### *2.2.1.4 Io*

Io is about the same size as the Moon, is the innermost of Jupiter's satellites, and has one of the largest densities of any Solar System moon [15]. It has some of the most active volcanoes in the Solar System. These volcanic eruptions are likely attributed to gravitational tidal stresses caused by Jupiter's mass. Io's orbit and its relationship to Europa, Callisto, and Ganymede also contribute to the tidal stresses [7].

Voyager 1 observed a number of Io's volcanic eruptions. Io's volcanoes vigorously eject sulfur compounds into the atmosphere. A portion of this material produces a ring around Jupiter. The degree of volcanic activity creates a relatively smooth surface with few observable craters [7].

Io has a number of unique surface features that are enhanced by the volcanism. It has liquid sulfur lakes, mountains, and sulfur lava flows. Io's unique and varied coloration is attributed to the various sulfur compounds. In contract to Callisto and Europa, Io has minimal water.

The Galileo probe provided data regarding Io's core. The core is likely composed of iron with a diameter exceeding 900 km.

#### *2.2.1.5 Titan*

Saturn's moon Titan with a diameter of about 5200 km is the second largest moon in the Solar System [15]. Titan is larger than Earth's moon. It has a heavy atmosphere with thick clouds. The atmosphere is composed primarily of nitrogen with some methane and trace gases with a pressure of about 1.5 atm [7, 15]. The surface temperature is about 93 K [7].

The Cassini spacecraft and its Huygens lander were able to penetrate Titan's thick clouds. Additional data were provided by the Hubble Space Telescope. The surface appears to be relatively flat, and impact craters could be filled with hydrocarbon precipitation [7].

NASA's Cassini probe observed indications of erosion on Titan caused by a flowing liquid. It is likely that the liquid is methane and there are liquid methane lakes near Titan's poles [11]. The European probe Huygens was released from Cassini, traversed its dense atmosphere, and landed on the surface of Titan. Huygens data suggests that Titan has an orange color, and its atmosphere contains clouds that resemble smog [11].

#### *2.2.1.6 Triton*

Neptune's largest moon Triton has a diameter of about 2700 km and it orbits the planet in a retrograde manner [15]. It is possible that Triton's orbital characteristics are a consequence of its gravitational capture by Neptune [7]. Voyager 2 extended knowledge of Triton and its characteristics.

**13**

*Solar System Planets and Exoplanets*

100 times weaker than Earth's [7].

action of the Solar wind [7].

*2.2.2 Asteroid Belt*

configuration.

composition [7].

*2.2.1.7 Moon*

(~1.6 m/s2

*DOI: http://dx.doi.org/10.5772/intechopen.98431*

Triton has a thin nitrogen atmosphere, records a surface temperature of about 33 K, and exhibits active surface features [7]. It has a bright surface that may have been impacted by geyser-like eruptions that eject liquid nitrogen into the atmosphere [11]. Solar radiation is attributed to be the driving force for these geysers [7]. The surface appears to be relatively young since it has minimal surface craters. Triton is about 25% water ice with the remaining material being rocky in

NASA's Voyager 2 probe and the Hubble Space Telescope provided significant data regarding Neptune and its moons [7]. Additional probes and space missions

The Moon is Earth's only satellite. It has a diameter about 25% of Earth's, a mass

The second densest planetary satellite in the Solar System is Earth's moon [7]. It has a thin crust, thick mantle, and an iron core that is estimated to be less than 400 km in diameter. The Moon's surface is inactive with no apparent volcanic or tectonic activity [7]. In addition, there is a minimal magnetic field approximately

The Moon's surface contains numerous craters, dark areas that appear to be flat (*mare*), and basins that were created by impacts that subsequently filled with lava that has solidified [7]. The bright regions are mostly mountains and other elevated areas. The Moon's far side has minimal *mare* areas [7]. Its surface has a thin layer of fine particles of powered surface rock (regolith). NASA's Apollo missions provided

The Moon's has essentially no atmosphere. Some material (e.g., radon gas) is released from the surface through radioactive decay. Other material is generated through micrometeorite impact and sunlight interactions with surface materials. However, much of the atmospheric constituents are swept from the Moon by the

Several thousand bodies (asteroids) reside between 2 and 3.5 AU between the orbits of Mars and Jupiter [15]. This region is known as the Asteroid Belt. The largest of these is Ceres that contains about one third of the Asteroid Belt mass, and has a radius of about 500 km that is smaller than the Solar satellites summarized in **Table 4** [15]. Solar probes have investigated the properties of Asteroid Belt bodies. For example, NASA's space probe Dawn orbited Vesta that is one of the largest asteroids, and also investigated Ceres [11]. Some asteroid bodies have orbits that

Some Solar System planets contain small moons that have a rocky composition that is similar to the Asteroid Belt bodies. It is possible that some of these moons were once asteroids that were gravitationally captured by the planets during an early phase of Solar System evolution when orbits were less stable than the current

**Table 5** lists the largest asteroids and their physical characteristics. A portion of the data was derived from the Dawn spacecraft. The mass values are rough estimates provided by NASA [25]. Ceres is classified as a dwarf planet [7]. Vesta, Pallas, and

Juno and are the second, third, and fourth heaviest asteroids, respectively.

considerable Lunar data including the return of sample materials to Earth.

intersect Earth's orbit and present a potential collision hazard [7].

). The Moon's orbit is tidally locked, and the same side faces the Earth [7].

about 0.01 times the mass of Earth, and its surface gravity is about one sixth g

are required to better characterize Neptune and its moons.

#### *Solar System Planets and Exoplanets DOI: http://dx.doi.org/10.5772/intechopen.98431*

Triton has a thin nitrogen atmosphere, records a surface temperature of about 33 K, and exhibits active surface features [7]. It has a bright surface that may have been impacted by geyser-like eruptions that eject liquid nitrogen into the atmosphere [11]. Solar radiation is attributed to be the driving force for these geysers [7].

The surface appears to be relatively young since it has minimal surface craters. Triton is about 25% water ice with the remaining material being rocky in composition [7].

NASA's Voyager 2 probe and the Hubble Space Telescope provided significant data regarding Neptune and its moons [7]. Additional probes and space missions are required to better characterize Neptune and its moons.
