7-15. Solar System Fundamentals Goals: 1. Learn the basic astrophysics of solar system objects. 2. Introduce basic solar system terminology, which differs from other areas of astronomy. 3. Discuss some of the rationale behind searches for other planetary systems.

Consider the case of a small black sphere of radius a and albedo A orbiting the Sun at a distance of r A.U. from it. Albedo = fraction of incident light reflected. The radiance at the Sun’s surface is σT 4 where T  = 5779 K. The surface area of the Sun is 4πR  2, so the total emergent radiant flux from the Sun is = 4πR  σT  4. At a distance r from the Sun, a small disk of radius a intercepts a fraction of the Sun’s light amounting to:

The amount absorbed by the sphere is (1−A), where A is the albedo of the sphere. So the radiant flux absorbed by the sphere is: The absorbed energy heats the sphere, which reradiates it into space. If T bb is the black body temperature of the ball when it reaches equilibrium, then the total energy reradiated by the sphere is:

For equilibrium, the total radiant energy absorbed by the sphere must be equal to the total radiant energy reemitted, so. or: For R  =  10 8 m and T  = 5779 K one can calculate the expected temperature of various spheres of differing A as a function of orbital radius r in the solar system.

Insertion of values for the Sun, and normalization of the distances in terms of A.U. produces: For a slowly-rotating planet the temperature of the sunlit side, T ss, is given by:

PlanetPredicted T bb Observed T Mercury440K~650 K 625 K (noon) Venus229 K210 K (clouds), 750 K (surface) Earth246 K290 K Moon 273 K,~205 K 386 K (noon) Mars216 K~230 K Jupiter102 K150 K (cloud tops)

Note that this also predicts an exponentially decreasing temperature T with increasing distance r from the Sun (or any star).

Planeta (A.U.)R/R  M/M  Mercury Venus Earth Moon Mars Jupiter Saturn Uranus Neptune Pluto

Distances from the Sun: Mercury0.4 D  Venus 0.7 D  Earth 1.0 D  Mars 1.5 D  Jupiter 5.2 D  Saturn 9.6 D  Uranus 19.2 D  Neptune 30.1 D  Pluto 39.8 D  Distances from the Sun: Mercury0.4 D  Venus 0.7 D  Earth 1.0 D  Mars 1.5 D  Jupiter 5.2 D  Saturn 9.6 D  Uranus 19.2 D  Neptune 30.1 D  Pluto 39.8 D 

Some Men Very Early Made All Jars Stand Up Nearly Perpendicular

Say ! My Very Energetic Maiden Aunt Just Served Us Nine Pizzas

Sun Mercury Venus Earth Mars Asteroids Jupiter Saturn Uranus Neptune Pluto

Mnemonic Mostly Nonsense Easing Memorization Of Names In Columns

The Asteroid Belt

The Terrestrial Planets Earth + 1Venus + 0 Mercury + 0 Mars + 2 Moon

The Ringed Gas Giants Earth + 1 Uranus + 27 Neptune + 14 Jupiter + 67 Saturn + 62

The Plutinoes Earth + Moon Pluto + 5 Kuiper-Edgeworth Belt Objects Eris + 1

Planets − Bright “stars” on the ecliptic.

Jupiter and Venus

Waning Crescent Moon, Venus & Jupiter.

Comets

Comet Tails

Comet Origins Kuiper Cloud

Comet Origins Oort Cloud

Shepherd Satellites

Tides F~1/r 3

Tidal Friction

Displays of the aurora borealis imaged by Wilf Meyer from Yellowknife.