The Solar System

Question 1

What is the approximate radius of the solar system in AU?

Answer 1

30 AU

Question 2

What are the two types of planets in our solar system?

Answer 2

Inner terrestrial planets and the outer giants.

Question 3

What are asteroids?

Answer 3

Smaller solar system bodies (large rocks etc).

Question 4

What is the definition of a planet?

Answer 4

A celestial body that is in orbit around the Sun, has sufficient mass for self-gravity to overcome rigid body forces and overcome hydrostatic equilibrium, and has cleared the neighbourhood around it’s orbit.

Question 5

What is the definition of a dwarf planet?

Answer 5

A celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium, and has not cleared the neighbourhood around its orbit. Not a satellite.

Question 6

What is the Oort cloud?

Answer 6

Large asteroid belt surrounding the solar system.

Question 7

What is a comet tails radiation pressure?

Answer 7

Photons have momentum p = E/c = hv/c, and radiation field thus exerts an apparent force, Frad = dp/dt, equivalent to a pressure of Prad = F/area

Question 8

What is the equation for the radiation pressure due to the Sun at distance d?

Answer 8

Prad = (dE/dt)/(4picd^2) = L (sun) / (4picd^2)

Question 9

What is the equation for gravity and radiation for a dust grain with size r at distance d? What does the ratio of these forces mean?

Answer 9

gravity: m GM/d^2 = (4/3 * pi * ρ * r^3) * GM/d^2
radiation: (L(sun)/(4picd^2) x pi*r^2

Ratio of these two forces is independent of distance to Sun, but scales as 1/r.

Question 10

What is the equation for temperature of a planet in equilibrium?

Answer 10

Teq = (L(sun)/16piσd^2)^(1/4)

Question 11

Why do planets form in a disc?

Answer 11

• Collapsing cloud of gas, angular momentum of one “blob” of gas is l=vr
• From Keplers law, l = sqrt(GM)/r *r = sqrt(GMr)
• DIsc configuration minimises collisions and potential energy.

Question 12

What does the graph of temperature in Kelvin against distance from Sun in AU look like?

Answer 12

Constant negative gradient, with temperature ranging from 10^3 to 10^3, and distance in AU ranging from 10^0 to 10^2

Question 13

What happens in the inner zone of the solar system?

Answer 13

Gases escape by radiation pressure, clumps of metal rich dust - compact terrestrial planets.

Question 14

What happens in the middle zone of the solar system?

Answer 14

Lots of ice, good gas condensation and clumping - gas giants and icy giants.

Question 15

What happens in the outer zone of the solar system?

Answer 15

Methane ice, no collisions - Kuiper Belt with small objects

Question 16

What is the equation for the temperature of a planet to be habitable?

Answer 16

Tp = T*sqrt(R/2d) - liquid water

Question 17

Approximately how many exoplanets are known?

Answer 17

3500

Question 18

What are the two methods for detecting exo-planets?

Answer 18

Wobble (transit) and doppler shift.

Question 19

How does the transit method work for detecting exo planets?

Answer 19

As the exo planet orbits a star, we can see a drop in the intensity of the star, meaning something is passing in front of it - could be an exo planet. If planet is not in plane of view, may make the star “wobble” due to gravity.

Question 20

What is the equation for the doppler shift of light due to velocity v?

Answer 20

λ’ = λ0*(1+v/c), where λ’ is the observed wavelength and λ0 is the rest wavelength.