Dusty Disks -- ? Pictoris ~ 107 -108 years old
First discoverd via infrared excess by IRAS satellite
- infrared emission from dust orbiting star
- many small dust grains much easier to see than planets
- Surface area much larger for a given amount (volume) material
- Human lung has surface area of 80 m2
- ~ size of the floor of this classroom
- area from many tiny alveoli ~ 0.01 mm in diameter
- demo with Post-It notes
- when spread out scatter much more light
- same reason Comets are bright when near the sun
- dust boils off the surface to produce coma and tail
- area/volume ratio 1013 times bigger for dust grains than planet
- dust heated by starlight to about 100 K
- peak emission at 30,000 nm, i.e. infrared
- cf. star radiates at 300 nm (i.e. 10,000 K)