Lecture 14: Formation of Planets

Question 1

what is the basic way in which planets form?

Answer 1

cloud of gas and dust collapses due to self-gravity overcoming thermal pressure

angular momentum causes cloud to spin faster as it collapses, then settling into thin disc

star forms in the centre, planets form in the proto- stellar discs

Question 2

how do we estimate the disc lifetime?

Answer 2

existence can be inferred from the infrared excess radiation (J, H, K, L wavelength bands)

Question 3

how might solids grow in the disc?

Answer 3

solids condense to form micron-sized grains

grains collide and grow to cm-sized pebbles, km-sized planetesimals

large planetesimals sweep up small ones to grow

Question 4

what is the snow line?

Answer 4

disc heated by radiation from protostar

temperature decreases with radius

heavy elements condense to form small grains at large radius

boundary beyond which gas giant planets form and inside which terrestrial planets form

this is because there is more solid, planet-building material beyond the snow line