Astronomy Exam 3

Planets, Dwarf Planets

Explain why Mercury is the most challenging planet to view from Earth. What is the best way to overcome this challenge?

difficult to observe due to its close proximity to sun and its small size. Observing Mercury during its greatest elongation, when it is farthest from the sun in the sky, is the best way to view it.

What is the process of radar ranging? Describe how this process is used to determine the distances to planets. What other information about a planet can be determined via this technique?

a technique that involves sending radar signals to a planet and measuring the time it takes for the signals to return. This process allows astronomers to calculate the distance to the planet and can also provide data on its surface characteristics, rotation, and atmosphere.

How is the core of Mercury different from the cores of the other terrestrial planets?

unusually large, comprises about 75% of its radius, which is significantly larger than the cores of other terrestrial planets. composed mainly of iron

Describe why Mercury’s atmosphere has become so tenuous.

its low gravity, which is unable to hold onto gases, and its close proximity to the Sun, which causes any gases to be stripped away by solar wind.

What is a scarp? By what process do astronomers say formed the scarps on Mercury?

extended cliffs along the surface. it’s caused by uneven internal cooling.

Describe how the Caloris Basin formed. How is the formation of the Caloris Basin related to the hilly terrain located on the opposite side of the planet?

formed from a massive impact event early in Mercury's history, creating a large crater. This impact caused seismic waves that generated hilly terrain on the opposite side of the planet, known as the "Anti-Caloris" region.

Where do astronomers think water ice has been found on Mercury? How does this relate to NASA’s LCROSS mission

Polar craters, high radar albedo detected along bottoms near the north pole.

Orbital resonance is any situation where the orbit of an object is synchronized with some other movement. Describe the orbital resonance of Mercury. How has this
affected the length of the solar day on Mercury? What effect has this had on the surface conditions?

Orbital resonance of Mercury refers to its 3:2 spin-orbit resonance, meaning it rotates three times for every two orbits around the Sun. This affects the length of the solar day, making it longer than its rotational day, resulting in extreme temperature variations on its surface.

What is meant by the precession of Mercury’s orbit? What is its importance to our
understanding of how gravity works

Precession of Mercury's orbit refers to the gradual shift in the orientation of its elliptical orbit over time. This phenomenon is significant as it provides evidence for the predictions of General Relativity, enhancing our understanding of gravitational forces.

List the properties of Venus that are similar to Earth. What are some of its’ differences?

size, mass, and surface gravity. However, it differs significantly in atmospheric conditions, with a thick carbon dioxide atmosphere and extreme greenhouse effect, resulting in much higher surface temperatures.

What is a transit? How often does Venus transit the Sun? Why doesn’t Venus transit the Sun more regularly? What other planet(s) will be seen to transit the Sun from Earth?

An astronomical event where a planet passes directly between the Earth and the Sun, appearing as a small dot moving across the Sun's face. Venus transits the Sun approximately every 121.5 years, and it doesn’t transit more regularly due to its tilted orbit relative to the Earth's plane. Mercury is another planet that can be seen to transit the Sun from Earth.

What prevents us from observing the surface of Venus directly from Earth? How do
astronomers work around this issue?

Its thick atmosphere makes it difficult to observe. Astronomers use radar mapping and surface landers to penetrate the clouds and study the surface.

How does the geologic activity of Venus compare to that of Earth?

Venus exhibits geologic activity such as volcanism and tectonics, but it lacks plate tectonics like Earth. Its surface shows evidence of relatively recent volcanic activity and a lack of erosion, suggesting a dynamic geology.

How do the atmospheric conditions of Venus compare to those of Earth?

Venus has a thick, toxic atmosphere primarily composed of carbon dioxide, with clouds of sulfuric acid, resulting in a strong greenhouse effect and surface temperatures hot enough to melt lead.

Describe the runaway greenhouse effect. Explain why Venus and Earth ended up with such different atmospheric conditions.

The runaway greenhouse effect occurs when a planet's atmosphere traps heat, leading to increasing temperatures that prevent the escape of greenhouse gases. Venus experienced this effect due to its proximity to the Sun and its thick carbon dioxide atmosphere, while Earth's more moderate conditions and presence of liquid water allowed it to maintain a stable climate.

In what ways are Mars and the Earth similar?

Mars and Earth share similarities such as having polar ice caps, seasons due to axial tilt, and evidence of past water flow, indicating they once had more Earth-like conditions. The only other terrestrial world with natural satellites, and it has a similar rotation period which yields a similar solar day.

How is the atmosphere of Mars similar to Venus? In what ways is it different?

Mars has a thin atmosphere primarily composed of carbon dioxide, similar to Venus; however, it lacks the thick clouds of sulfuric acid and the extreme greenhouse effect. This results in much lower surface temperatures and conditions that are less hostile to potential life.

Due to it having a similar axial tilt, Mars will experience seasons very similar to Earth’s. How are changes in the seasons on Mars visible from Earth

through its polar ice caps and dust storms, which can be observed through telescopes.

What is the reason Mars ended up with a reddish-brown color to its surface?

The reddish-brown color of Mars is primarily due to iron oxide, or rust, on its surface, which reflects sunlight and gives it its distinctive hue.

How does Olympus Mons compare to similar structures found on Earth? What led to the formation of Olympus Mons?

Olympus Mons is the largest volcano in the solar system, significantly larger than any volcano on Earth. Its formation is attributed to the lack of tectonic plate movement on Mars, allowing lava to accumulate over time and create its massive shield shape.

How does Valles Marineras compare to similar structures on Earth? What is thought to be the process that led to its formation?

Valles Marineris is a vast canyon system on Mars, significantly larger than the Grand Canyon, showcasing tectonic activity and erosion processes that may have shaped its formation.

What evidence is there that liquid water once flowed heavily on the surface of Mars??

There are various features on Mars, such as river valleys, lake beds, and mineral deposits, that suggest the past presence of liquid water. Additionally, data from orbiters and rovers have detected signs of ancient water flows and sedimentary rock formations.

Is there any evidence of liquid water on Mars today?

Yes, there are indications of briny water flows, particularly in recurring slope lineae, as well as ice deposits detected by orbiters and rovers.

What missions/experiments have been performed in an effort to find life on Mars?

Various missions, including NASA's Mars rovers (like Curiosity and Perseverance) and the Viking landers, have searched for signs of microbial life, analyzed soil and rock samples, and studied the planet's atmosphere for biosignatures.

What is the current state of affairs with regards to the search for life on Mars?

Ongoing missions, such as Perseverance and Curiosity rovers, are exploring the Martian surface for signs of past life, while orbiters analyze the atmosphere and surface for potential biosignatures. The search includes studying Martian soil and rocks for organic compounds and monitoring seasonal changes in surface features.

What is the overall chemical composition of Jupiter?

Jupiter is primarily composed of hydrogen and helium, with trace amounts of methane, water vapor, ammonia, and other compounds.

Describe the process of belt/zone circulation.

Belt or zone circulation refers to the large-scale movement of air in Earth's atmosphere, driven by solar heating and the planet's rotation. This creates distinct wind patterns, including the trade winds in the tropics, westerlies in the mid-latitudes, and polar easterlies near the poles, forming three main atmospheric cells: Hadley, Ferrel, and Polar cells.

Describe the Great Red Spot. How large is it? How strong is it? When was it first
observed? What has been happening to it recently

massive, persistent storm on Jupiter. about 16,000 kilometers (10,000 miles) wide, roughly 1.3 times the diameter of Earth, can reach speeds of up to 432 km/h (268 mph). It was first observed in 1665 by astronomer Giovanni Cassini. The Great Red Spot has been shrinking in size over the past few decades and is also becoming more circular in shape.

Describe the JUNO mission.

The JUNO mission is a NASA spacecraft mission to study Jupiter. The mission aims to learn about Jupiter’s atmosphere, magnetic field, and internal structure to understand the planet's formation and its role in the solar system

What is the Roche Limit of a planet? What is the connection between the Roche Limit and the location of a planet’s ring system?

minimum distance from a planet at which a moon or other object held together by its own gravity will be torn apart by the planet's tidal forces. This occurs when the planet's gravitational force exceeds the object's self-gravity. helps explain the location of a planet's ring system. Rings typically form within or near the Roche Limit, where the planet’s tidal forces prevent objects (like moons or debris) from coalescing into a single body. Instead, the material remains as a spread-out ring of particles. If a moon or object moves within this limit, it may be torn apart and contribute to the formation of a ring system.

What is liquid metallic hydrogen? Where is this material found on Jupiter?

a phase of hydrogen that exists under extreme pressure, where hydrogen behaves like both a liquid and a metal. In this state, hydrogen atoms are compressed so much that their electrons become free, allowing the material to conduct electricity like a metal. in the planet's interior at pressures and temperatures so high (around 1-3 million times Earth's atmospheric pressure and temperatures over 10,000 K) that hydrogen becomes metallic. It is thought to make up a significant portion of Jupiter's core region and outer interior.

What makes Saturn’s density so unique?

the least dense of all the planets in the solar system. Its average density is lower than water, about 0.687 grams per cubic centimeter. This low density is due to Saturn being primarily composed of hydrogen and helium, which are light gases, and its overall size (about 95 times the mass of Earth) compared to its volume.

Why is Saturn’s ring system so noticeable? How is Saturn’s ring system different from the ring systems of the other giant planets?

it is the largest and brightest of any planet in the solar system, made up of billions of ice and rock particles that reflect sunlight. Saturn's rings are much more extensive, primarily made of ice particles, which reflect sunlight and make them appear bright and reflective, thick and well-defined, whereas the rings of the other giant planets are much thinner and less distinct.

Who discovered Uranus? Describe how it was discovered.

Uranus was discovered by William Herschel on March 13, 1781. He found it while using a telescope to survey the night sky, originally thinking it was a star. Upon further observation, he realized it was a planet, making it the first planet to be discovered with a telescope.

Describe what makes Uranus’ rotational axis unique

Uranus' rotational axis is unique because it is tilted at an extreme angle of about 98 degrees. This means Uranus essentially rolls on its side as it orbits the Sun, with its poles pointing nearly directly at the Sun. Most planets have their axes tilted by a few degrees, but Uranus’ extreme tilt results in very unusual seasonal changes and extreme variations in sunlight across its surface.

How was Uranus’ ring system discovered?

Uranus' ring system was discovered in 1977 by James L. Elliot and his team using the Kuiper Airborne Observatory. They observed the planet as it passed in front of a star (an event called a stellar occultation), and noticed that the star's light dimmed in a series of patterns. This revealed the presence of faint rings around Uranus, which were blocking the starlight in distinct intervals.

What makes the discovery of Neptune unique as compared to other planets?

The discovery of Neptune is unique because it was predicted before it was directly observed. In the 1840s, astronomers noticed irregularities in the orbit of Uranus that couldn't be explained by known forces. Using mathematical calculations, Johann Gottfried Galle and Heinrich d'Arrest discovered Neptune on September 23, 1846, based on predictions made by Urbain Le Verrier and John Couch Adams, who independently calculated the planet's location. This made Neptune the first planet to be discovered through mathematical theory rather than direct observation.