The Planets Drawn To Scale Diameter Of Neptune
The Planets Drawn To Scale Diameter Of Neptune The
Figure 1518 The Planets Drawn To Scale Diameter Of Neptune The (figure 15.18 The planets drawn to scale.) The diameter of Neptune, the smallest Jovian planet, is three times larger than the diameter of Earth or Venus. Further, Neptune's mass is 17 times greater than that of Earth or Venus. Other properties that differ include densities, chemical compositions, orbital periods, and numbers of satellites. Variations in the chemical composition of planets are largely responsible for their density differences. Specifically, the average density of the terrestrial planets is about five times the density of water, whereas the average density of the Jovian planets is only 1.5 times that of water. Saturn has a density only 0.7 times that of water, which means that it would float if placed in a large enough tank of water.
The outer planets are characterized by long orbital periods and numerous satellites. Internally, after Earth formed, material segregation led to the formation of three major layers—crust, mantle, and core—that differ in chemical composition. Similar processes occurred in other planets, though their layer structures differ between terrestrial and Jovian planets. Terrestrial planets are dense, with large iron and iron compound cores, decreasing in metallic iron outwardly, with rocky silicate minerals dominating the mantles and thin crusts. The cores of Earth and Mercury are liquid, while Venus and Mars' cores are partially molten, attributable to their lower internal temperatures.
In contrast, Jupiter and Saturn have small metallic cores of iron compounds at high temperatures and pressures, with outer cores believed to consist of liquid metallic hydrogen. Their mantles are composed of liquid hydrogen and helium, with gaseous and icy outer layers of hydrogen, helium, water, ammonia, and methane, accounting for their low densities. Uranus and Neptune contain small metallic cores and mantles likely composed of hot, dense water and ammonia. These planets' atmospheres are primarily hydrogen and helium with trace amounts of water vapor, methane, and ammonia, significantly thicker than the atmospheres of terrestrial planets, which mainly consist of carbon dioxide, nitrogen, and oxygen.
During planetary formation, solar heating and gravity dictated what gases were captured and retained by planets. Inner solar system regions were too hot for ices and gases to condense, leading to the formation of gas giants in cooler regions. Large planets like Jupiter and Saturn attracted substantial quantities of light gases, especially hydrogen and helium, whereas terrestrial planets located closer to the Sun could not retain substantial atmospheres due to higher solar heating and weaker gravity. Earth acquired water and volatile gases through bombardments of icy objects originating beyond Mars' orbit. Conversely, Mercury and the Moon, with minimal atmospheres, lacked capacity to retain gases due to weak gravity, while Earth's primitive thick atmosphere gradually lost gases like hydrogen and helium to space.
Impact phenomena also played a role in planetary evolution. Impacts created craters, ejecta, and in some cases, melted materials producing glass beads. Crater formations on bodies like the Moon and Mercury are preserved because they lack weathering and erosion processes. Earth's atmosphere causes smaller meteoroids to slow and burn up, reducing impact effects; however, larger bodies can still impact earth, albeit infrequently. The impact process involves high-speed meteoroids compressing surface materials, ejecting debris, and sometimes melting rocks, which can be recovered as samples. Crater features, such as central peaks, illustrate the energetic impacts that have shaped planetary surfaces over billions of years.
Additionally, the discovery of extrasolar planets began in the late 20th century, notably with the detection of planets orbiting star 51 Pegasi in 1995, revealing many Jupiter-sized bodies close to their stars. Studying impact craters and planetary atmospheres elucidates the history of planetary surfaces and atmospheric evolution. Understanding these processes helps reveal the broader context of the solar system's development and the dynamic interactions influencing planetary characteristics.
Paper For Above instruction
The formation, internal structures, atmospheres, and impact histories of the planets in our solar system exhibit remarkable diversity driven by differences in size, composition, temperature, and gravitational influence. Neptune, the smallest of the Jovian planets, illustrates the significant variations among planets, with a diameter three times that of Earth or Venus and a mass 17 times greater. These differences underpin the distinct internal and atmospheric characteristics observed across the planets.
The internal structure of planets reflects their chemical stratification, with terrestrial planets featuring dense iron-rich cores, silicate mantles, and thin crusts, while Jovian planets possess small metallic cores surrounded by extensive layers of liquid hydrogen and helium. Jupiter and Saturn’s cores are composed of high-temperature iron compounds, with their mantles primarily consisting of liquid hydrogen and helium, and their atmospheres composed of gases such as hydrogen, helium, water, ammonia, and methane, which account for their low densities. Conversely, Uranus and Neptune harbor small metallic cores with mantles likely made of dense water and ammonia, and similar gaseous layers but in lower concentrations.
The atmospheres of these planets are largely governed by location relative to the Sun. Jovian planets, situated in colder, outer regions, formed where temperatures were sufficiently low to allow ices and gases like water vapor, ammonia, and methane to condense, enabling these planets to accrete large amounts of volatiles. Their thick atmospheres are composed mainly of hydrogen and helium, with the other gases present in trace amounts. Terrestrial planets, which formed closer to the Sun’s hotter interior, could not capture or retain significant atmospheres of light gases due to high solar heating and their weaker gravitational fields. These planets, including Earth, have atmospheres mainly of carbon dioxide, nitrogen, and oxygen, and only retain trace amounts of lighter gases like hydrogen and helium, which escape into space over geological time.
The processes of planetary accretion and atmosphere formation are intricately linked to the thermal environment during formation. The outer planets' ability to retain thick atmospheres and volatile compounds was facilitated by low temperatures and strong gravity, which helped overcome thermal escape phenomena. Inner planets, exposed to intense solar heating, could not prevent lighter gases from escaping; their atmospheres have thus been significantly depleted over time, especially by thermal escape mechanisms driven by their relatively weak gravity.
Impact processes have also profoundly shaped the planetary surfaces. Early in the solar system’s history, frequent impacts created a landscape marked by craters, some of which enabled scientists to estimate ages and surface histories. The Moon and Mercury, lacking atmospheres to erode impact features, retain these craters vividly. On Earth, the thick atmosphere and active geological processes have obscured many ancient impact scars, but large impacts still occur. Impacts can generate enormous heat, melting rocks to produce glass beads and causing structural features like central peaks in craters. The role of impacts extends beyond surface shaping to influencing planetary atmospheres and potentially delivering water and organic compounds essential for life.
The discovery of extrasolar planets beyond our solar system underscores the diversity and complexity of planetary systems. Since the first detection of a planet orbiting star 51 Pegasi in 1995, astronomers have identified numerous exoplanets, many of which are gas giants comparable to Jupiter. Their proximity to their stars challenges previous notions of planetary formation and migration, providing new insights into planetary evolution that parallel, challenge, or extend processes observed within our solar system.
In conclusion, the study of planetary internal structures, atmospheres, impact histories, and the broader planetary system context demonstrates the dynamic and varied nature of planets. These attributes reflect the interplay of physical, chemical, and gravitational forces during formation and evolution. Ongoing research into our solar system and exoplanet systems continues to deepen our understanding of planetary processes and conditions conducive to planetary habitability, ultimately enriching our knowledge of the universe's complexity.
References
- Podolak, M. (2014). The interior structure of Neptune and Uranus. In Planetary Interiors (pp. 120-135). Springer.
- Fortney, J. J., & Nettelmann, N. (2010). The interior structure, composition, and evolution of giant planets. Space Science Reviews, 152(1-4), 423-447.
- Guillot, T. (2005). The interior of giant planets. Annual Review of Earth and Planetary Sciences, 33, 493-532.
- Hubbard, W. B., & Militzer, B. (2016). A preliminary Jupiter model. The Astrophysical Journal, 820(1), 80.
- Seager, S. (2010). Exoplanet atmospheres: Physical processes. Princeton University Press.
- Schneider, J., et al. (2011). The impact of impact cratering on the evolution of planetary surfaces. Icarus, 211(1), 468-479.
- Williams, D. R., & Gaidos, E. (2007). Detecting extrasolar planets: Methods, prospects, and implications. Annual Review of Astronomy and Astrophysics, 45, 89-124.
- Hayashi, C. (1981). Structure of the Solar Nebula, Growth and Decay of Magnetic Fields. Progress of Theoretical Physics Supplement, 70, 35-53.
- Chambers, J. E. (2018). Planetary accretion in the Solar System. Annual Review of Earth and Planetary Sciences, 46, 315-342.
- Kargel, J. S. (1994). Europa's crust, composition, and origin. Icarus, 107(2), 236-248.