Week 2: Orbits and Tides Flashcards
Define all 3 Laws of Kepler in words
1) K1: All planets move along elliptical paths with the Sun at one of the focus
2) K2: A line connecting the planet and the sun sweeps out area at a constant rate, due to the conservation of angular momentum
3) Orbital period squared is proportional to semi-major axis cubed
Name 4 mechanisms causing changes to orbits
1) Collisions
2) Jets from comet nuclei
3) Yarkovsky effect
4) Jupiter’s gravitational influence
Define “circular restricted three-body problem”
An orbital system containing 3 bodies: 2 massive bodies in circular motion with each other, and 1 body of much smaller mass called a ‘test particle’.
Define the term “Lagrange points” and illustrate the relative position of L1, L2, L3
5 points where the test particle feels no net force in a circular restricted three-body problem.
What causes tides
Tides are caused by the fact that the gravitational force exerted by the moon on Earth is 7% stronger on the near side than on the far side, resulting in tidal force. This causes water to bulge at the equator, called a tidal bulge, as water moves to minimize PE and reach eqm.
The tidal force has 2 components: The radial component which stretches/ compresses material radially, and the tractive component which stresses material tangentially. It is the latter that pushes the water to the peak of the tidal bulge
Define the term “Roche limit” and state its approximations
The distance from a celestial body, below which a smaller body will be torn apart by tidal force.
Inside the Roche limit, an object will be disrupted by tidal force and debris will disperse to form rings
Outside the Roche limit, an object will be held together by self-gravity and debris will coalesce
Approximations:
1) Closely orbiting bodies have synchronous rotations with circular orbits
2) The limit only applies to stray bodies and high e orbits
