Astro Lecture 5 Flashcards
Q: What is the Solar Nebular Hypothesis?
The theory that our solar system formed from the gravitational collapse of a giant molecular cloud 4.6 billion years ago which was possibly triggered by a shock wave from nearby supernovae.
Q: What likely triggered the collapse of the molecular cloud that formed our solar system?
A shock wave from nearby supernovae which also enriched the cloud with elements only formed in massive star explosions.
Q: How long ago did the solar system form?
Approximately 4.6 billion years ago.
Q: How long did the planet-building process take?
Approximately 3-10 million years
Q: What direction do most planets rotate relative to their orbit?
Most planets rotate in the same direction as they orbit the Sun with Venus and Uranus being exceptions.
Q: What is the distribution of mass and angular momentum in the solar system?
The Sun contains 99.9% of the system’s mass while the planets have 99.7% of the angular momentum.
Q: How do the compositions of inner and outer planets differ?
Inner terrestrial planets are small, dense and made of silicates and metals; outer jovian planets are large, massive, and composed primarily of hydrogen and helium with abundant ices and volatiles.
Q: What is Earth’s composition by mass?
32% Iron, 30% Oxygen, 15% Silicon, 14% Magnesium, plus other elements.
Q: What is Jupiter’s composition by mass?
75% Hydrogen, 24% Helium, plus trace elements.
Q: What are the main phases of solar system formation?
1) Collapse Phase, 2) Contraction Phase, 3) Formation of Planetesimals, 4) Formation of Planets, 5) Clearing of leftover material
Q: What happens during the Collapse Phase of solar system formation?
A large, irregular, weakly rotating cloud of gas begins to collapse due to gravitational forces.
Q: What occurs during the Contraction Phase of solar system formation?
Most mass collects at the center forming the Sun, while the remaining material forms a disk that increases its spin, flattens, heats up, and becomes more dense.
Q: How do planetesimals form?
As the disk cools, solid particles begin sticking together, growing through accretion until they form approximately 1 km chunks called planetesimals.
Q: What causes the end of the planet formation process?
The Sun fully igniting and generating solar wind that cleared out remaining gas and dust.
Q: How do planets form from planetesimals?
Once planetesimals reach sufficient size, they gravitationally attract each other and surrounding materials, growing into planets.
Q: What are asteroids and where are they primarily found?
Asteroids are rocky bodies left over from terrestrial planet formation, composed primarily of iron and silicates, and are mainly found in the Asteroid Belt between Mars and Jupiter.
Q: What are comets and what is their origin?
Comets are small icy bodies leftover from the formation of the jovian planets that were either deflected into the inner solar system or to the edges in the Oort Cloud or Kuiper Belt.
Q: What is the Kuiper Belt?
A region beyond Neptune containing various small icy bodies, including comets, dwarf planets like Pluto, and other objects.
Q: What three criteria define a dwarf planet?
1) Large enough to be rounded by its own gravity, 2) Orbits the Sun (not a moon), 3) Too small to clear its orbital neighborhood.
Q: Name the five officially recognized dwarf planets.
A: Ceres (in the asteroid belt), Pluto, Eris, Haumea, and Makemake (in the Kuiper Belt).
Q: What is the Giant Impact Theory?
The theory that the Moon formed when a Mars-sized body collided with Earth approximately 50 million years after Earth’s formation, ejecting material that condensed to form the Moon
Q: How is Earth’s Moon unusual compared to other planet-moon systems?
Earth’s Moon is unusually large relative to its planet compared to most planet-moon systems.
Q: What challenge exists with the Giant Impact Theory regarding the Moon’s composition?
Explaining why the Moon’s composition so closely matches Earth’s, when it should contain more material from the impacting body.
Q: What is tidal locking and how does it affect the Moon?
Tidal locking occurs when an orbiting body’s rotation period matches its orbital period. The Moon is tidally locked to Earth, which is why we only see one side from Earth.
Q: How are the Earth and Moon moving relative to each other and why?
They are moving apart at approximately 4 cm per year due to tidal forces causing energy loss in the orbital system.
Q: How has the Earth-Moon system changed since the Moon’s formation?
When formed, the Moon was much closer (about 1/20th current distance), Earth’s day was only 5 hours, and the Moon orbited every 6.5 hours. Now they continue to move apart with Earth’s day lengthening.
Q: How might the Moon have contributed to the evolution of life on Earth?
1) It stabilized Earth’s rotation axis, creating a stable climate, and 2) Its tidal forces created tidal pools that may have provided ideal conditions for the formation of the first biological cells.
Q: What is a planetesimal?
Building blocks of planets, kilometer-sized bodies formed through accretion of smaller particles in the protoplanetary disk.
Q: What distinguishes a planet from a dwarf planet?
A planet has cleared its orbital neighborhood of other objects, whereas a dwarf planet has not.
Q: What is tidal locking?
When a celestial body’s rotation period equals its orbital period, causing the same side to always face the body it orbits.
Q: What causes tidal forces on Earth?
Differences in gravitational pull across Earth, with the side nearest the Moon experiencing stronger pull than the far side.
Q: Where is Sedna located and what is it?
Sedna is a potential dwarf planet located in the far outer solar system, discovered in 2003.
