*2.2.3 Comets and Kuiper Belt Objects*

In addition to moons and Asteroid Belt Objects, comets are another group of objects that orbit the Sun. Most comets are composed of a combination of rocky material, dust, and ice. A tail comprised of escaping dust and gases often characterizes comets. These materials are generated as the comet material evaporates. This evaporation is facilitated by the radiation pressure of the Sun, and the associated Solar wind of charged particles [15].

#### *2.2.3.1 Comets*

Most comets are small bodies with diameters less than 1 km to as large as 300 km [30], and many of these bodies move in highly eccentric orbits. Comets often display bright heads and long tails due to the evaporation of ice when their orbits bring them in proximity to the Sun. These bodies are probably the remnants of planetesimals originally located in an outer region of the Solar System known as the Oort cloud that lies roughly between 3,000–100,000 AU. Comets also originate in the Kuiper Belt that lies between 30 and 1,000 AU. Their orbits can be altered by the Solar System planets particularly Jupiter [15].

Comets are often classified by their orbital period. Short- (long-) period comets have orbital periods of 200 years or less (greater than 200 years) [15].

#### *2.2.3.2 Kuiper Belt Objects*

A consideration of orbital parameters suggests that the likely source of shortperiod comets is the Kuiper Belt. This belt contains numerous icy bodies. A selected set of Kuiper Belt Objects is summarized in **Table 6**. The largest member of the known Kuiper Belt Objects is the dwarf planet Eris. The dwarf planets Pluto and Charon, one of its moons, are also among the largest Kuiper Belt Objects [15].

The long-period comets likely originate within the Oort Cloud that is a roughly spherically symmetric region of space. These comet nuclei represent ISM dating from the time of the formation of the Solar System [15].

**Table 6** summarizes a listing of the largest Kuiper Belt Objects. In addition to Pluto, some of these objects also have an associated moon. Eris is also similar to Pluto in terms of its composition. The reader should note that Sedna has a significantly larger orbit than many observed Kuiper Belt Objects. Given this consideration, the detection of additional Kuiper Belt Objects is possible [15]. One curious possibility, known as Planet Nine, is addressed in subsequent commentary.

**15**

*Solar System Planets and Exoplanets*

**Kuiper Belt Object Diameter** 

*2.2.3.2.1 Pluto*

*Derived from Ref. [15].*

*Largest Kuiper Belt Objects.a*

*a*

**Table 6.**

*2.2.3.2.2 Eris*

*2.2.3.2.3 Planet Nine*

of a number of Kuiper Belt Objects.

are summarized in **Table 6** [15].

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

**(km)**

Perturbations to Neptune's orbit suggested the existence of a new planet that led to the discovery of the dwarf planet Pluto. However, Pluto's mass is too small to have perturbed Neptune's orbit. The orbital perturbation issue involving other Kuiper Belt Objects has led to the speculation of additional Solar System planets [15, 29]. Pluto is likely composed of rock, and it has an icy surface mixture of frozen nitrogen with smaller amounts of carbon monoxide and methane. As such, Pluto's surface is similar to Triton [15]. It is believed to have a rocky core. Pluto has a very thin atmosphere that includes nitrogen, methane, and carbon monoxide [15]. This

**Orbital Period (y)**

2002 AW197 900 330 47 0.13 Varuna 900 280 43 0.052 Ixion 1100 250 40 0.24 Quaoar 1200 290 44 0.035 2003 EL61 1200 290 43 0.18 2005 FY9 1300 310 46 0.16 Charon 1300 250 39 0.25 Orcus 1500 250 39 0.22 Sedna 1600 12,000 530 0.86 Pluto 2300 250 39 0.25 Eris 2400 560 68 0.44

**Semimajor Axis (AU)**

**Eccentricity**

composition is consistent with the sublimation of surface material [15].

that has a circular orbit with a rotational period of about 16 days.

Pluto has a diameter of about 2300 km and has a rotation period of about 6.4 days. It has five moons [28]. Pluto's largest moon (Charon) and its characteristics

Eris is an additional dwarf planet that is slightly larger than Pluto. It has a radius about 20% of Earth's. The internal structure of Eris is unknown [27]. Ref. [15] suggests that its surface is similar to Pluto that incorporates a composition of frozen methane, rock, and ices of various elements including nitrogen. Eris' surface temperature is about 33 K [27]. This dwarf planet also has a small moon Dysnomia

Periodically, predictions of additional planets beyond Pluto have been made. One of the more recent developments is an assertion by Batygin and Brown [12]. Ref. [12] suggests the existence of an additional planet with a mass of approximately 10 Earth masses, and an orbit at about 20 times farther from the Sun than Neptune. Their estimates for Planet Nine were inferred from observed orbital characteristics

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


### **Table 6.**

*Solar System Planets and Exoplanets*

*2.2.3 Comets and Kuiper Belt Objects*

*Selected Asteroid Belt data derived from Ref. [25].*

Solar wind of charged particles [15].

Solar System planets particularly Jupiter [15].

from the time of the formation of the Solar System [15].

*2.2.3.2 Kuiper Belt Objects*

*2.2.3.1 Comets*

**Table 5.**

Ceres is believed to have a rocky core [7]. An icy mantle and crust surround the core. The mantle could be as thick as 120 km and contain a volume of water greater

**Asteroid Mass (kg) Rotation Period (h) Orbital Period (y) Eccentricity** Ceres 9.4x1020 9.1 4.6 0.076 Pallas 2.1x1020 7.8 4.6 0.23 Juno 2.0x1019 7.2 4.4 0.26 Vesta 2.6x1020 5.3 3.6 0.089

In addition to moons and Asteroid Belt Objects, comets are another group of objects that orbit the Sun. Most comets are composed of a combination of rocky material, dust, and ice. A tail comprised of escaping dust and gases often characterizes comets. These materials are generated as the comet material evaporates. This evaporation is facilitated by the radiation pressure of the Sun, and the associated

Most comets are small bodies with diameters less than 1 km to as large as 300 km

Comets are often classified by their orbital period. Short- (long-) period comets

A consideration of orbital parameters suggests that the likely source of shortperiod comets is the Kuiper Belt. This belt contains numerous icy bodies. A selected set of Kuiper Belt Objects is summarized in **Table 6**. The largest member of the known Kuiper Belt Objects is the dwarf planet Eris. The dwarf planets Pluto and Charon, one of its moons, are also among the largest Kuiper Belt Objects [15].

The long-period comets likely originate within the Oort Cloud that is a roughly spherically symmetric region of space. These comet nuclei represent ISM dating

**Table 6** summarizes a listing of the largest Kuiper Belt Objects. In addition to Pluto, some of these objects also have an associated moon. Eris is also similar to Pluto in terms of its composition. The reader should note that Sedna has a significantly larger orbit than many observed Kuiper Belt Objects. Given this consideration, the detection of additional Kuiper Belt Objects is possible [15]. One curious possibility, known as Planet Nine, is addressed in subsequent commentary.

[30], and many of these bodies move in highly eccentric orbits. Comets often display bright heads and long tails due to the evaporation of ice when their orbits bring them in proximity to the Sun. These bodies are probably the remnants of planetesimals originally located in an outer region of the Solar System known as the Oort cloud that lies roughly between 3,000–100,000 AU. Comets also originate in the Kuiper Belt that lies between 30 and 1,000 AU. Their orbits can be altered by the

have orbital periods of 200 years or less (greater than 200 years) [15].

than the Earth's oceans. Ceres has a surface temperature of about 233 K [7].

**14**

*Largest Kuiper Belt Objects.a*
