• initial attempts to produce orbit for Uranus unsuccessful

• 1821: Bouvard produces orbit based on contemporary observations

• includes gravitational influences of Jupiter and Saturn

• discrepancy possibly due to gravitational perturbations of an unknown planet

• deviations between prediction and observations (perturbations) increase with time

Problem: use the observed perturbations to predict location of the unknown

NEPTUNE

Adams (English)• approximate method to determine location and mass (1843) • used Newton's laws of Mechanics and Gravitation • assumed circular orbit, twice the radius of Uranus' • dropped assumptions when more accurate data obtained• calculated orbit and mass of the unknown (1845) • orbit presented to Challis and Airy at Cambridge Observatory • search delayed due to concerns of Challis and Airy

LeVerrier (French)

• determined size of perturbations very precisely by examining effects of Jupiter and Saturn • assumed orbit fit T-B law (38.8 AU) • also used Newton's Laws • produced ephemeris (August, 1846)

The Race

• Adams becomes aware of Leverrier's work , requests Challis begin search for object• Challis begins observing (July 1846) • Cambridge lacked detailed sky maps of region • necessitates large amount of data analysis, Challis reluctant

• uses new Star Map of the Berlin Academy (created in response to discovery of asteroids)• locates a new object within 52' of prediction• Galle and Enke confirm object moves

• Leverrier's ephemeris sent to Galle at Berlin Observatory (Sept. 23, 1846)

• must be planet - Neptune

The Aftermath

• British had observed Neptune on Aug. 4 and 12 • didn't analyse the observations until after discovery at Berlin• controversy over credit • Galileo may have observed it in 1612-13 • Neptune's orbit has radius of 30.1 AU, period 164 years • T-B law discredited • discovery added credence to Newton's theories

• LeVerrier examines Mercury's orbit • perihelion advance (1.5° per century) • gravitational perturbations account for all but 40" of the advance • suggested existence of another planet (Vulcan)- never found

Mercury

PLUTO

• Uranus' orbit apparently still had unaccounted perturbations • Lowell predicts position of another unknown object • Clyde Tombaugh searches for planet at Lowell Observatory• uses blink comparator• Feb. 1930: discovers object within 6° of Lowell's prediction – Pluto

• perturbations of Uranus were not produced by Pluto

Pluto and Charon

• orbit: 39.5 AU, period 248 years

MOONS AND MINOR BODIES

• many new moons discovered as telescope resolution improves • 1877 - 2 moons of Mars

• Jupiter - 63, Saturn - 34

• 1978 - Pluto's moon Charon• 2005 - 2 more moons for Pluto (discovered with HST)

Phobos

Deimos

• collection of rocky/icy bodies out to 50,000 AU • home of long-period comets

Kuiper Belt (1951)• rocky objects beyond Pluto, out to 500 AU • home of short-period comets • Quaoar, Sedna - similar to Pluto

Sedna

Quaoar’s orbit

• Eris (2006) - larger than Pluto

Oort Cloud (1950)

• round due to gravity

• not heavy enough to clean majority of nearby space

• Pluto, Ceres

Trans-Neptunian Objects

Dwarf Planets (August 2006)