ASTR1003 Planets Practice Exam Questions

Q1: What is the significance of the term “Planet” and its origin in ancient Greek?

• Originates from the Greek word planetos meaning “wanderer”

• Described bright celestial bodies moving differently than stars

• Applied to Mercury, Venus, Mars, Jupiter, and Saturn

Q2: What three clues about the motion and characteristics of planets contributed to the development of the heliocentric theory proposed by Copernicus?

• Venus and Mercury always appear close to the Sun

• Venus shows crescent phases; Mars, Jupiter, Saturn do not

• Jupiter’s moons orbit it, proving not all celestial bodies orbit Earth

Q3: What problem did accurate observations, particularly those by Tycho Brahe, pose for the heliocentric model, and how was this issue addressed?

• Observations showed heliocentric model couldn’t predict planet positions precisely

• Elliptical orbits replaced circular ones to improve accuracy

Q4: Is it accurate to say “there is no air in space”? What would be a more accurate statement about air in space?

• Not accurate; a better statement: air is so sparse that wind resistance is negligible

Q5: Is there gravity in space, and why do astronauts appear weightless in space stations?

• Gravity exists in space

• Astronauts are in continuous free-fall, creating a sensation of weightlessness

Q6: In space, why does an object keep moving in a straight line after being pushed, and how does the concept of “free-fall” explain weightlessness experienced by astronauts?

• No friction or resistance = straight-line motion

• Free-fall around Earth causes the sensation of weightlessness

Q7: What are the two different ways to explain orbits, and how does centrifugal force contribute to maintaining an orbit?

• Sideways motion + gravity = continuous falling around Earth

• Centrifugal force balances gravity depending on speed and altitude

Q8: What determines the shape of an orbit, and how do different speeds result in circular, elliptical, or escape trajectories?

• Right speed = circular orbit

• Slightly faster or slower = elliptical orbit

• Much faster = escape trajectory (parabolic/hyperbolic)

Q9: What method was used to measure the distances within the solar system? And what unit is typically used to measure distances within the solar system?

• Method: Parallax (measuring angle differences from two viewpoints)

• Unit: Astronomical Unit (AU)

Q10: How do astronomers measure the properties of objects in space, specifically concerning distance, size, and mass?

• Distance: signal timing or radio wave bounces

• Size: images + angular size

• Mass: gravity’s effects on moons or orbits; estimated using density if needed

Q11: What are the main features of the Sun, and how does its mass compare to the combined mass of the planets in the solar system?

• Contains 99.85% of solar system’s mass

• Dominates in size, mass, and brightness

Q12: What distinguishes Gas Giants (Jupiter and Saturn) from Ice Giants (Uranus and Neptune), and what is the likely composition of their interiors?

• Gas Giants: mostly hydrogen and helium, fast cloud layers, possible metallic cores

• Ice Giants: more ices like water, methane, ammonia, and denser interiors

Q13: What are the categories of objects in the solar system, and what distinguishes Ice Worlds from Rocky Planets?

• Rocky Planets: small, dense, solid (e.g., Earth, Mars)

• Gas Giants: large, mostly gas

• Ice Giants: smaller, icy cores

• Ice Worlds: frozen surfaces (e.g., Pluto, Triton)

Q14: What distinguishes the atmosphere of Earth, Venus, Mars, and Mercury, and how do their atmospheres compare in thickness?

• Earth: thick atmosphere

• Venus: very dense but thin layer over surface

• Mars: thin atmosphere

• Mercury: no atmosphere

Q15: What is the significance of the common composition of the Sun and meteorites, as revealed by spectroscopy?

• Similar compositions = common origin

• Suggests Sun and planets formed from the same cloud

Q16: Explain the role of angular momentum in the formation of a protoplanetary disk, and why disks are inevitable during the formation of stars and planets.

• Angular momentum increases as cloud collapses

• Spinning causes formation of a flat disk around the new star

Q17: What role do solid grains play in the formation of planets in the protoplanetary disk, and what are the likely compositions of these grains in the inner and outer regions of the disk?

• Grains = building blocks of planets

• Inner disk: rocky grains

• Outer disk: icy grains (water, methane)

Q18: How do planets form from the solid grains in the protoplanetary disk, and what is the role of collisions in shaping the final configuration of the solar system?

• Grains → pebbles → planetesimals through collisions

• Final planet formation shaped by giant impacts and gravitational interactions

Q19: How do gas giants like Jupiter and Saturn form, and why do they have significantly larger sizes than other objects in the solar system?

• Reached a critical mass to attract hydrogen and helium

• Became large due to gas accumulation

• Uranus and Neptune didn’t grow large enough to capture much gas

Q20: How do scientists determine the chemical composition of planetary bodies in the outer solar system, where direct sampling is not feasible?

• Use spectroscopy to analyze light spectra

• Identify materials remotely using telescopes and orbiters

Q21: How does gravity impact the shape of celestial bodies, and what is the effect on mountains and overall appearance on planets and asteroids?

• Stronger gravity = smoother planets

• Weaker gravity = irregular shapes, taller mountains

Q22: What are the two main causes of craters on planets and moons, and how do they differ in terms of their geological features?

• Meteorite impacts: crater dips below surface

• Volcanic craters: raised and centered on volcano tops

Q23: How does the debris from a meteorite impact contribute to the geological composition of celestial bodies like Mars and the Moon, and what significance does it hold for studying these surfaces?

• Ejecta spreads rock fragments across surface

• Helps scientists study diverse regions from one sample

Q24: What is the primary factor causing the difference in crater density between the lunar highland regions and the Mares? How could dating Moon rocks help verify this difference?

• Highlands are older → more craters

• Rock dating confirms age differences and crater history

Q25: How does potassium-argon dating work, and why is argon-argon dating considered a more convenient method for dating Moon rocks?

• K-Ar: measures decay of potassium-40 to argon

• Ar-Ar: easier, smaller sample, single instrument

Q26: Explain the concept of the “Late Heavy Bombardment” and its potential role in the Moon’s geological history. How does this event correlate with the age of lunar rocks?

• ~4 billion years ago: intense meteor impacts

• Mare rocks are younger; highlands show older impact record

Q27: How does the evidence of impact craters on planetary surfaces help in dating different regions within our solar system, and what insights can it provide about the geological history of these celestial bodies?

• More craters = older surface

• Crater counts help reveal resurfacing history

Q28: What plays a crucial role in maintaining the internal heat of small rocky planets like Earth and Venus, preventing them from cooling down and allowing volcanic activity to persist?

• Radioactive decay of isotopes like uranium maintains heat

Q29: What geological process is responsible for the formation and growth of Earth’s continents, and how does this process relate to the distribution of land and ocean on the planet?

• Mantle convection + volcanic activity creates lightweight crust

• Low-density rocks form floating continents

Q30: Describe the geological features observed on Venus and explain why it lacks evidence of plate tectonics, contrasting it with Earth’s geological processes.

• Few impact craters = recent resurfacing

• Flat volcanoes, uniform terrain

• Lacks water, which may be key to Earth’s tectonics

Q31: Explain the formation of volcanic features on Mars, such as Olympus Mons, in comparison to volcanic formations on Earth. How does the absence of plate tectonics on Mars contribute to the development of these colossal volcanoes?

• Mars’ fixed hotspots allow volcanoes to build up over time

• Earth’s moving plates prevent this kind of growth

Q32: Why do moons like Io, Europa, and Enceladus, despite being smaller than rocky planets like Mercury, have active volcanoes?

• Tidal heating from gravitational interactions keeps them geologically active

Q33: How does Pluto’s geology differ from that of larger rocky bodies, and what unusual features were observed during the New Horizons mission?

• Frozen nitrogen glaciers, water ice mountains

• Little to no craters in some areas

• Possible cryovolcanoes

Q34: How does the James Webb Space Telescope achieve its cooling for optimal infrared observations, and why is this method effective?

• Uses sunshields to radiate heat away

• Enables ultra-cold conditions for infrared detection

Q35: What is responsible for the smaller temperature ranges on planets with atmospheres, such as Earth, compared to vacuum worlds like the Moon?

• Atmospheres transport heat via convection and circulation

Q36: What role does gravity play in retaining an atmosphere, and why do smaller planets tend to have thinner atmospheres or none at all?

• Strong gravity holds onto gases

• Smaller planets can’t retain lighter gases

Q37: Titan, Saturn’s moon, has a thick atmosphere despite being smaller and less massive than Mars. What factors contribute to Titan’s substantial atmosphere?

• Cold temperatures reduce gas escape

• Less solar wind due to distance

• Composition allows ices to vaporize into gases

Q38: The “Greenhouse Effect” is a phenomenon that warms a planet by trapping outgoing infrared radiation. Which gases in a planet’s atmosphere contribute to this effect, and how do they accomplish it?

• CO₂, H₂O, CH₄ absorb and trap infrared heat

• Allow sunlight in, block heat from escaping

Q39: Why does Venus have such a thick atmosphere of carbon dioxide, and how does its isotope ratio provide insights into its atmospheric history?

• Runaway greenhouse effect evaporated water

• Deuterium/hydrogen ratio suggests past water loss

• No plate tectonics to bury CO₂ into rocks

Q40: What geological features on Mars indicate the presence of liquid water during the Noachian and Hesperian periods, and what challenge does Mars’ early warm and wet history pose in light of the Sun’s brightness at that time?

• Features: water channels, deltas, clay minerals

• Problem: Sun was ~30% dimmer, hard to explain warmth

Q41: How does Earth’s past climate compare to its present climate, and what factors have influenced these changes over geological time?

• Past: warmer periods (dinosaurs), ice ages

• Factors: greenhouse gases, atmospheric changes, human influence

Q42: Why were the objects discovered between Mars and Jupiter initially classified as planets, and what led to their later classification as “asteroids”?

• Initially called planets due to motion

• Reclassified as asteroids due to small size and faint appearance

Q43: What are the Trojan asteroids, and why are they safe from Jupiter’s gravitational influence?

• Located at Lagrange points (L4 & L5)

• Gravitationally balanced zones = stability

Q44: What is the “Grand Tack” model, and how does it explain the formation and characteristics of the asteroid belt?

• Jupiter moved inward then outward

• Scattered and cleared the asteroid belt

• Explains low mass and mixed types in the belt

Q45: What are the three main types of asteroids based on their spectra, and what types of meteorites are associated with each?

• C-type → carbonaceous chondrites

• S-type → stony meteorites

• X/M-type → metallic meteorites

Q46: What is the significance of the iridium layer found at the Cretaceous-Paleogene boundary, and how does it support the theory of a meteorite impact causing a mass extinction event?

• Iridium rare on Earth, common in meteorites

• Global iridium layer supports impact theory

Q47: How do Near Earth Asteroids potentially originate from the main asteroid belt?

• Caused by collisions and solar radiation

• Altered orbits → Kirkwood gaps → gravity assists → Earth-crossers

Q48: How does the risk of asteroid impacts vary based on their size, and what is the potential impact on human civilization?

• Small: frequent, low damage

• Medium: regional destruction

• Large (1–10 km): global catastrophe

Q49: How do telescopes in programs like the US Spaceguard detect asteroids, and what has been the outcome of these surveys?

• Use wide-field images + software to track motion

• ~95% of large (1km+) asteroids found

• Focus now on smaller 100m ones

Q50: How can the orbit of an asteroid be changed to prevent a potential collision with Earth, and what are some proposed methods for diverting asteroids?

• Impact mission (e.g. DART)

• Gravity tug, sunlight pressure, nukes (speculative)

Q51: What was the phenomenon initially observed on Mars that triggered a widespread belief in the existence of intelligent life, and what were these features believed to be?

• “Canals” (misinterpreted channels) seen as artificial

• Believed to be built by intelligent Martians

Q52: Why would the discovery of bacteria in space be significant, and what does it suggest about the potential ubiquity of life in the universe?

• Unrelated = life can form independently → life may be common

• Related = panspermia possible (life transfer between worlds)

Q53: What are the key considerations for searching for microbial life beyond Earth, and why is Mars considered a potential candidate for past or present life?

• Look for water, hydrocarbons

• Mars had liquid water → life could exist or have gone underground

Q54: Why is the presence of liquid water on moons like Enceladus, Europa, and Callisto considered significant in the search for extraterrestrial life?

• Subsurface oceans = potential habitats

• Life on Earth thrives without sunlight → same could apply

Q55: Why is colonization seen by many as an immoral practice, particularly from an Indigenous perspective?

• Involves land theft, racism, slavery, destruction of environment and culture

Q56: What three arguments in favour of colonizing the solar system?

• Survival (safe haven from disasters)

• Social innovation (new societies)

• Population/resource pressure relief

Q57: What are the key factors to be considered when choosing a location for space colonization, and why are gas giants, Venus, and the icy bodies in the outer solar system initially excluded from potential colonization options?

• Need water, minerals, moderate temps, pressure, radiation protection

• Gas giants lack solid surfaces

• Venus is too hot; outer icy bodies are too far/cold

Q58: Why might the Moon be a potential candidate for colonization, and what unique challenges does it pose for human settlement?

• Close to Earth, has minerals, some polar water

• No atmosphere, extreme temperatures, radiation risks

Q59: What advantages do robots have over humans for space exploration and colonization, and how might artificial intelligence play a role in the future of space activities?

• No life support needed

• Can withstand extreme environments

• AI could lead future colonization efforts, even replicate human minds