**2.1 Solar System planets**

*Solar System Planets and Exoplanets*

large body collided with the planet.

the orbits of Mars and Jupiter.

the terrestrial and gas giant planets.

ing life?

references.

discovered.

exoplanetary systems.

utilizing the accompanying reference list.

**2. Planetary overview**

which led to these bodies generally having more moons than the less massive terrestrial planets. Some moons were formed by planetary gravitational capture of rocky structures and asteroid fragments. Other moons (e.g., Earth's moon) formed when a

Following the creation of the initial planets and their moons, the Solar System still contained considerable debris that collided with these bodies. The Moon's craters are an example of the effect of the resulting impact of this debris. Some of this debris, particularly icy structures, formed beyond Neptune's orbit and as is known as the Kuiper Belt. An Asteroid Belt comprised of rocky structures formed between

This simplified model of planetary creation has been supplemented with a bifurcation model. Within the bifurcation model, planet formation occurred in spatially and temporarily distinct domains through a postulated mechanism that was driven by the presence of water [24]. Although the details of this mechanism are unknown, the domains evolved in distinct physical modes with different volatile materials. Model calculations suggest that these physical differences led to the formation of

As the capability to observe exoplanetary systems and their atmospheres improves, it will be interesting to determine if the characteristics of the Solar System and life on Earth are unique. Will further exoplanet observations reveal a variety of star and planetary systems having the capability of sustain-

The reader should note that the literature provides a range of values for planetary data including their associated composition. Given this consideration, specific references are cited when particular data are noted. Significant figures are usually

Although Solar System planets have been studied for centuries, the observation of exoplanets is only a few decades old. The first exoplanet orbiting a star outside the Solar System (i.e., 51 Pegasi), discovered by Mayor and Queloz [2], did not occur until 1995. Since that time, progress in exoplanet discovery and characterization has increased rapidly. As of January 2021, 4341 exoplanets have been

General characteristics of Solar System planets are addressed in Section 2.1 and other Solar System bodies (i.e., planetary moons, the Asteroid Belt, comets, Kuiper Belt Objects, and meteoroids) are discussed in Section 2.2. Section 2.3 is devoted to a discussion of exoplanets. Exoplanet detection methods are provided in Section 3. Section 4 summarizes the variety of space probes utilized to examine planetary and

The presentation of this chapter is designed to facilitate the flow of subsequent material. Selected content provides an overview of subsequent chapters. Since there are numerous references to the characteristics of Solar System planets and exoplanets, the presentation of this chapter is necessarily incomplete. However, the text does provide an overview of the subject and the basis for more detailed study

This chapter provides a general overview of Solar System planets and exoplanets. It's intended to introduce these systems to readers not well versed in planetary science. Additional planetary details are provided in this chapter's

provided to accommodate the variation in literature values.

**4**

There are eight Solar System planets as well as dwarf planets, planetary moons, the Asteroid Belt, comets, Kuiper Belt Objects, and meteorites. These spatial bodies are addressed in subsequent discussion.

An overview of the Solar System planets and a general classification scheme is summarized in **Table 1**, and illustrated in **Figure 1**. The Solar System planets can be grouped in terms of structural characteristics with the terrestrial planets being compact objects that are primarily rocky objects. Gas giant planets are a combination of gas, rock, and ice.

The terrestrial planets are closest to the Sun and are smaller, warmer, and less massive than the gas giants. Although more massive, the gas giants have a lower density. The gas giants have more moons and exhibit ring structures. These general characteristics are summarized in **Table 1**.

**Table 2** provides additional data for the Solar System planets including their orbital characteristics (i.e., distance from the Sun, orbital period, and orbital eccentricity). Their surface gravitational acceleration in m/s2 is also provided. These data are important for spacecraft and probes attempting to investigate these worlds. Detailed orbital calculations are required to plan missions that would reach these planets, and successfully orbit and land on these worlds [4].
