What is the solar nebula theory?
A theory that the solar system formed from a rotating cloud of gas and dust that collapsed under gravity, flattened into a disk, formed the Sun at the center, and planets from the surrounding material.
What evidence supports the solar nebula theory?
Planets orbit in the same direction, lie in nearly the same plane, and the Sun contains most of the mass.
Where did the atoms in our solar system originate?
Hydrogen and helium from the Big Bang, heavier elements from stars and supernovae.
How old is the solar system and how is this determined?
About 4.6 billion years old, determined using radioactive dating of meteorites.
What is half-life?
The time required for half of the radioactive atoms in a sample to decay into daughter elements.
What are the main characteristics of planetary orbits?
Nearly circular, lie in the same plane, and orbit the Sun in the same direction.
What defines a planet (IAU definition)?
Orbits the Sun, is spherical due to gravity, and has cleared its orbital region of debris.
What are terrestrial planets?
Small, dense, rocky planets with thin or no atmospheres (Mercury, Venus, Earth, Mars).
What are Jovian planets?
Large, low-density planets made of gas/ice, with many moons and rings (Jupiter, Saturn, Uranus, Neptune).
How do terrestrial and Jovian planets differ?
Terrestrial = small, rocky, dense; Jovian = large, gaseous/icy, low density, many moons/rings.
What is the asteroid belt?
A region between Mars and Jupiter containing rocky debris that failed to form a planet.
What are comets made of and what happens near the Sun?
Ice and dust; they form tails of gas and dust when heated near the Sun.
Where do short-period and long-period comets originate?
Short-period: Kuiper Belt; Long-period: Oort Cloud.
What is the difference between a meteoroid, meteor, and meteorite?
Meteoroid = rock in space; Meteor = streak of light in atmosphere; Meteorite = reaches Earth’s surface.
What is the condensation sequence?
The order in which materials condense from the solar nebula based on temperature and distance from the Sun.
What is the ice line?
The distance from the Sun beyond which temperatures are low enough for water vapor to freeze into ice.
Why is the ice line important for planet formation?
Beyond it, ices can form, providing more material and allowing Jovian planets to grow large
What is a planetesimal?
A small solid body formed from dust and gas that can grow into a protoplanet.
What is accretion?
The process where solid particles stick together to form larger bodies.
What is condensation (in planet formation)?
Growth of particles atom-by-atom from surrounding gas.
What is a protoplanet
A growing planetary body formed from collisions of planetesimals.
What happens when a protoplanet reaches ~15 Earth masses?
it undergoes rapid growth by gravitational collapse, pulling in large amounts of gas.
What is outgassing?
The release of gases from a planet’s interior to form an atmosphere.
What was the heavy bombardment period?
An early period of intense impacts on planets during the first ~0.5 billion years.
