Homework 12 Uranus and Neptune
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Dec 6, 2023
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Science 105 Homework #12 Uranus and Neptune
1. Why is the discovery of Neptune rated as one to the triumphs of science, whereas the discoveries of Uranus and Pluto are not? - The discovery of Neptune was the result of mathematical predictions based on observed irregularities in the orbit of Uranus. Le Verrier
and Adams independently calculated the position of Neptune, and their predictions were remarkably accurate. Johann Galle, a German astronomer, observed Neptune for the first time within one degree of the predicted location. Uranus was discovered by Sir William Herschel in 1781. Unlike Neptune, its discovery was accidental. Herschel observed an object in the night sky that he initially thought was a comet but later realized was a new planet. Pluto's discovery was part of a systematic search for a ninth planet (Planet X) beyond Neptune. Clyde Tombaugh, an American astronomer, discovered Pluto in 1930 based on images taken at the Lowell Observatory. Pluto turned out to be much smaller than
originally thought and did not have the gravitational influence to explain the observed perturbations in the orbits of Uranus and Neptune. It was later reclassified as a dwarf planet. In summary, the discovery of Neptune stands out as a triumph because it was a successful application of theoretical predictions to locate a celestial object not yet observed. In contrast, Uranus was discovered accidentally, and Pluto's discovery, while part
of a systematic search, did not resolve the perturbation issues that led to the prediction of Neptune. The scientific process involved in the discovery of Neptune highlighted the power of mathematics and theory in advancing our understanding of the cosmos.
2. Briefly describe the evidence supporting the idea that Triton was captured by Neptune. - The idea that Triton, Neptune's largest moon, was captured by the planet rather than forming in orbit around it is supported by several lines of evidence. Here are some key points that contribute to the theory of Triton's capture: Triton has a retrograde orbit, meaning it moves in the opposite direction of Neptune's rotation. Most large moons in the solar system, including Neptune's other major moons, have prograde orbits, aligning with the planet's rotation. Triton's retrograde orbit is highly unusual in this context. Triton's retrograde orbit is indicative of a capture rather than a formation in orbit. The tidal forces exerted by Neptune on Triton would have caused significant tidal heating. The formation of
a moon in orbit around Neptune with Triton's current characteristics is considered dynamically unlikely. Simulations suggest that Triton's retrograde orbit would have been unstable if it formed in place, making the capture scenario a more plausible explanation. The regular moons of Neptune, which have prograde orbits, are thought to have formed in the circumplanetary disk around Neptune. Triton's retrograde orbit is inconsistent with the prograde orbits of Neptune's other regular moons, supporting the idea that Triton has a different origin. The evidence supporting Triton's capture by Neptune provides valuable insights into the dynamic processes that have shaped the moons and planets in our solar system.
3. Both Uranus and Neptune have a blue-green tint when observed through a telescope. What
does this color tell you about their atmospheric compositions? - The blue-green tint observed in the atmospheres of both Uranus and Neptune is indicative of the presence of methane in their atmospheres. The specific coloration is a result of how methane interacts with sunlight. Methane in the atmospheres of Uranus and Neptune absorbs red light, allowing the blue and green components of the sunlight to scatter and dominate the observed color. This absorption of red light by methane is a characteristic feature that contributes to the distinctive coloration. Rayleigh scattering, the phenomenon responsible for the blue color of the Earth's sky, also plays a role in the coloration of Uranus and Neptune. In the upper atmospheres of these gas giants, where scattering is more prominent,
the shorter wavelengths of light (blue and green) are scattered more effectively than the longer wavelengths (red), further enhancing the blue-green appearance. Both Uranus and Neptune have predominantly hydrogen and helium atmospheres, but they also contain significant amounts of methane, as well as traces of other hydrocarbons and gases. The presence of methane and its unique optical properties contribute to the observed color. Unlike Jupiter and Saturn, where ammonia plays a role in giving the atmospheres a more whitish appearance, Uranus and Neptune have a relatively low abundance of ammonia.
The absence of significant amounts of ammonia contributes to the distinctive blue-green coloration. It's important to note that while the methane absorption is a major factor in the coloration of Uranus and Neptune, other atmospheric components, and conditions, such as cloud cover and scattering processes, also influence the observed colors. The study of these
colors provides valuable information about the composition and atmospheric conditions of these ice giant planets.
4. How can small worlds like Triton and Pluto have atmospheres when larger bodies such as Ganymede do not? - The presence or absence of atmospheres on small worlds like Triton, Pluto, and larger bodies like Ganymede is influenced by various factors, including mass, temperature, and the specific composition of each celestial body. Triton and Pluto are believed to have volatile-rich compositions, including ices such as nitrogen, methane, and carbon monoxide. Triton, with its retrograde orbit around Neptune, likely originated in the Kuiper Belt and was captured by Neptune's gravity. Pluto is a Kuiper Belt Object (KBO) and a dwarf planet. As these bodies approach the Sun, the heat causes these volatile ices to sublimate (change from solid to gas), creating an atmosphere. The Sun's energy causes the ices on Triton and Pluto to sublimate and create temporary atmospheres. When these bodies move farther from the Sun, the atmospheres may collapse or freeze out due to the decrease in solar radiation. Both Triton and Pluto experience seasonal changes as they orbit
the Sun, impacting the presence and characteristics of their atmospheres. The tilt of their
axes and elliptical orbits contribute to variations in solar heating. Ganymede, Jupiter's largest moon, has a higher mass compared to Triton and Pluto. The higher gravity on Ganymede makes it more capable of retaining an atmosphere. However, Ganymede's atmosphere is extremely tenuous and thin. Ganymede has a composition that includes water ice, but it lacks the abundance of volatile compounds like nitrogen and methane found on Triton and Pluto. The scarcity of easily sublimating ices reduces the capability of Ganymede to maintain a significant atmosphere. Ganymede's distance from the Sun results in extremely cold temperatures, which further limits the ability of volatile ices to sublimate and form a substantial atmosphere. In summary, the presence of atmospheres on small worlds like Triton and Pluto is linked to their volatile-rich compositions and their proximity
to the Sun, leading to sublimation of ices. Larger bodies like Ganymede, while having the capability to retain an atmosphere, have limited volatile content and extreme cold conditions, resulting in a thin and tenuous atmosphere.
5. Why do you think that Triton had a geologically active past? What sources of energy could
have powered such activity? - Triton, Neptune's largest moon, is believed to have had a geologically active past, and several lines of evidence support this hypothesis. The key indicators of past geological activity on Triton include surface features such as cantaloupe terrain, ridges, valleys, and cryovolcanic features. The sources of energy that could have powered this activity are related to tidal forces and the interaction between Triton and Neptune: Tidal Heating: Triton is in a retrograde orbit around Neptune, meaning it moves in the opposite direction of the planet's rotation. This results in strong tidal forces between Triton and Neptune. Tidal heating occurs when a moon experiences gravitational forces that deform its shape as it moves through varying gravitational fields. This flexing generates internal heat. The tidal heating process is a significant source of energy that could have kept Triton's interior warm, leading to geological activity. Orbital resonances can lead to increased tidal forces, further enhancing the internal heating and geological activity. Features on Triton's surface, such as dark streaks and plumes, suggest the presence
of cryovolcanism—eruptions of volatile ices rather than molten rock. Tidal stresses and convection in Triton's interior could have contributed to the formation of this distinctive terrain. triton’s relatively smooth surface, with fewer impact craters than expected, indicates that some regions have undergone global resurfacing events. Cryovolcanic activity, possibly driven by tidal heating, could have played a role in erasing or modifying impact features on Triton's surface. In summary, Triton's geologically active past is likely the result of a combination of factors, with tidal heating being a primary source of energy. The retrograde orbit, resonances, and interactions with other moons have contributed to the
tidal forces that drove internal heating processes. The evidence of cryovolcanism and surface deformation supports the notion that Triton experienced geological activity in its history.
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