• 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)