graph:

horizontal axis - planetary mass in units of Earth masses

top of graph - equivalent value in Jupiter masses

vertical axis - planetary radius in earth masses

right axis - equivalent Jupiter radii

green dots are planets in our solar system

red dots - extrasolar planets where both mass and radius are known, which means it was discovered with the transit method for radius and follow-up observations with the Doppler method for mass

once you know the mass and radius you can calculate the densities

3 dashed curves represent particular densities

the middle curve represents the density of water (1 gram per cubic centimeter)

dots to the left of the middle curve have lower densities

dots to the right of the middle curve have higher densities

left curve represents the density of styrofoam

the left curve represents the density of iron

all planetary systems should form from material that is 98% or more hydrogen and helium and the remainder in the form of hydrogen compounds, rock, and metal

yellow color swath - planets with rock and metal like terrestrial planets

pink swath - planets made mostly of hydrogen and helium

blue swath - planets made mostly of hydrogen compounds

hot Jupiters - planets similar in composition to Jupiter but with larger radii and higher surface temperatures and surprising because they’re close to their stars

hot jupiters most likely formed in the outside part of the solar system and then migrated close to their stars

Super-Earths - planets similar in composition to Earth but more massive

water worlds - planets that are made predominantly of water, either solid or liquid

Detecting Earth’s planets from other stars is like trying to see a ball on a ball-point pen from 4,000 km away

Indirect planetary detection methods

1. Observing a star’s motion caused by the gravity of orbiting planets; the Doppler method and astrometric method

2. Observing changes in a star’s brightness as planets pass in front of it; transit method

larger Doppler shift = larger velocity

velocities are negative when an object is moving towards us and positive when it is away from us

the time from one peak to the next peak on a velocity curve represents the orbital period

the maximum height of the velocity curve represents the maximum velocity

the orbital period of the planet must be equal to the orbital period of the star around the system’s center of mass

If one star has a planet that is more massive than the planet orbiting another star, the planet will cause the star to move at a faster speed

For a particular orbital distance, the force of gravity depends on the product of the two masses.

If two objects of the same mass are attracting each other gravitationally, each time you double the distance you square the first number