12) Formation of Planetary Systems Flashcards
What is a Protoplanetary disc?
A Protoplanetary disc is a rotating disk of dense gas and dust surrounding a newly formed star
What is a frost line?
A frost line marked the boundary beyond which it was cold enough for volatiles to freeze onto tiny particles of dust; within the frost line, only metals and rock could condense into solid grains
How did the planets form?
Accretion
What is accretion?
Accretion is when small grains of solid material collide and stick into each other forming larger flakes. These collide into other pieces forming larger and larger bodies.
How long did it take before the accreted pieces formed the cores of planets?
After ~100 million years, the accumulated pieces formed the metallic and silicate cores of the planets
What happened to the bodies beyond the frost line?
Beyond the frost lines, the cores of the protoplanets grew to much bigger sizes due to the large abundance of ices. The gravitational attraction of these massive cores were able to draw in large amounts of hydrogen and helium that were present in the outer solar system to form the atmospheres of four gas giant planets
What factors affect the presence of an atmosphere?
A planet’s or moon’s mass
Temperature
Magnetic Field
How does temperature affect the presence of an atmosphere?
The hotter the temperature, the faster the gas molecules move, making them more likely to escape the gravitational attraction of the planet or moon
How does a planet’s mass affect the presence of an atmosphere?
The greater the mass, the greater the gravitational pull on the atmosphere
How many bodies were there estimated to be in the early solar system?
50 bodies
Why are there only 8 bodies currently in the Solar System?
The 50 bodies collided, broke apart and re-formed a significant number of times before becoming an ordered system with stable orbits around the Sun
How is Mercury evidence for previous collisions?
Mercury’s iron core occupies over 60% of its volume; the planet is thought to have lost most of its rocky interior due to a collision with a protoplanet about one sixth of its size
How does axis tilts provide evidence for previous collisions?
The backwards spin of Venus and sideways spin of Uranus suggests that these two planets had significant collisions during the Solar System’s history
What is tidal heating?
Tidal heating is when internal friction and the interior of a Moon becomes warm
What happens during tidal heating?
Thermal energy is produced at the expense of rotational kinetic energy, and the moon’s spins slows down a little. Over time, this results in a synchronised rotation where the Moon’s rotational and orbital period are the same
How is energy transferred during tidal heating?
The Internal friction produces energy which heats up the moon
What happens when the moon’s rotation becomes synchronised with it’s orbit?
Tidal heating doesn’t end because most moon orbits aren’t perfectly circular: A varying orbital speed means that tidal bulges still occur and oscillate about a mean position
What is the orbital interaction between various bodies called?
Orbital Resonance
How does orbital resonance work?
Orbital Resonance works when the different moons are aligned and and ‘tugged’ out of shape meaning they don’t have circular orbits
What is tidal heating responsible for?
Tidal heating is responsible for the molten layers that are beneath the rocky or icy crusts of large moons. This is responsible for active volcanoes or cryovolcanoes (ice volcanoes)
What happens if a moon’s elastic forces aren’t strong enough?
If a moon’s internal elastic forces that resist deformation aren’t strong enough, the tidal forces will break up the body or prevent one from forming
How are planetary rings formed?
Planetary rings are believed to be formed after a moon was broken up by tidal forces and the fragments spread around the planet
What is the Roche Limit?
The Roche limit is the minimum distance a large satellite can approach its parent body without being torn apart
What are the Lagrangian points?
The Lagrangian points are the stable positions near large objects in orbit. These are the points where a small object is able to orbit
How can a Satellite be stable in the Lagrangian points?
The Lagrangian points in a two body system (an example is the Earth and Sun) at which their combined force of gravity is equal to the centripetal force needed to maintain the circular motion of a third object (a satellite)
What are Exoplanets?
Exoplanets are planets that orbit a star outside the Solar System
What observation methods of stars can you use to discover exoplanets?
- Astrometry
- Transit Method
- Radial Velocity Method
What is Astrometry?
Astrometry is when massive Exoplanets orbit their star and their combined gravitational pull can cause the star to move or wobble slightly in its position around the common centre of gravity