*2.2.4 Meteorites*

The collision of asteroids produces a collection of smaller objects known as meteoroids. These collisions produce trajectories governed by the gravitational interaction of Solar System bodies. When a meteoroid enters the atmosphere of a planet, it is heated by friction and becomes a meteor. If the meteor strikes the planet's surface, its surviving fragments are called meteorites [15].

Meteorite material is also produced by the fracturing of comets that are exposed to the increased heat of the Sun particularly in the vicinity of the inner Solar System planets. These occurrences often lead to showers of micrometeorites that impact a planet's atmosphere [15].

Meteorites play a key role in planetary development. By depositing chemical elements or prebiotic material, meteorites can influence the evolution of a plant during its formative years. The extent of this influence depends on their size, frequency of impact, and composition. Meteorites striking a mature planet can cause ecological harm including impacts on the climate.

#### **2.3 Exoplanetary Systems**

Exoplanets are planets that orbit stars outside the Solar System. Given the diversity of star types and sizes, exoplanets have a wider range of physical characteristics than the planets that inhabit the Solar System. The various types of exoplanets include the most massive or gas giant planets, intermediate mass or Neptune planets, and low mass planets that include terrestrial and ocean planets or water worlds [9, 26]. Although most exoplanets orbit their host stars, rogue exoplanets are also possible [8].

### *2.3.1 Gas Giants*

Gas giant exoplanets are similar to Jupiter and Saturn. Their composition is dominated by hydrogen and helium with smaller contributions from heavier elements and complex molecules. Their structures may include cores of rock or ice [9, 15, 26]. However, a recent publication suggests that hot Jupiters could exhibit a more diverse chemical composition [34]. For example, an analysis of HD 209458b atmospheric data suggests the presence of water, carbon monoxide, hydrogen cyanide, methane, ammonia, and acetylene [34].

Hot Jupiters are a classification of gas giants that typically reside near their star usually within 0.05 to 0.5 AU [23]. They could have formed near their host star or migrated toward the star after forming at a more distant location. Given the proximity to their host star, temperatures can exceed 2,000 K [23]. Considering their size and proximity to their host star, they are readily detected and are one of the most common types of exoplanet detected to date. A commentary of detection methods is presented in subsequent discussion.

**17**

*Solar System Planets and Exoplanets*

*2.3.2 Neptune Class*

*2.3.3 Terrestrials*

planets Neptune and Uranus [23].

zone where liquid would water could exist [23].

the ice melted, and covered the planet in an ocean [23, 26].

Earths could be Chthonian Planets [23].

*2.3.4 Water worlds*

**3. Detection methods**

radius, and density [23, 33].

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

Neptune are representative of this class of planets.

Exoplanets known as the Neptune class are also giant planets, but heavy elements comprise most of their mass [9, 26]. The Neptune class of exoplanets has a thick hydrogen and helium layer, but these elements are not the dominant constituents as they were in the gas giants. Within the Solar System, both Uranus and

Uranus and Neptune are Solar System analogues of Neptune class exoplanets. These systems have a characteristic blue color. They are also known as ice giants because many models suggest that the bulk of the planet's mass resides within a sea that probably is comprised of ammonia, methane, and water [9]. However, there is likely a significant diversity in the composition of Neptune class exoplanets.

Terrestrials are exoplanets that are similar in structure to the inner planets of the Solar System including Mercury, Venus, Earth, and Mars. These exoplanets have compositions that are dominated by elements including carbon, oxygen, magnesium, silicon, and iron [9, 26]. Terrestrials are interesting because these bodies present the possibility of finding a planet similar to Earth that could support life. A sub-classification of terrestrials is Super-Earths. Super-Earths are rocky planets that have a mass greater than the Earth, but usually defined to be less than 10 Earth masses. Given their mass, some Super-Earths may be similar to Solar System

Exo-Earths are terrestrial exoplanets that have similarities to Earth in terms of their mass, radius, and temperature. Their orbits would reside within the habitable

Chthonian Planets are a proposed class of exoplanets that began as gas giants. During subsequent evolution, their orbits were altered to bring these planets in proximity to their host star. This proximity caused their atmosphere to be removed with only the rocky core remnant remaining. Given their similarity, some Super-

Exoplanets, referred to as ocean planets or water worlds, are dominantly comprised of water. Computer models suggest these exoplanets could be created by ISM enriched in icy material. As a candidate water world migrated toward the host star,

A number of detection methods have been utilized to observe exoplanets. These

Ref. [32] notes that in order to estimate an exoplanet's mass, the mass of the host star must be determined. The host star's mass estimate is based on its spectral type.

include, but are not limited to, transient methods, direct detection, and radial velocity measurements. Each of these three basic methods is addressed in subsequent discussion. If concurrent radial velocity and transient methods measurements are available, this combination can be used to determine the planet's mass,
