Small Bodies of the Solar System Pluto Comets

Small Bodies of the Solar System Pluto, Comets, Asteroids, Meteors and Zodiacal Light

PLUTO God of the Underworld

Pluto Physical Data • • Discovered by Clyde W. Tombaugh in 1930 Diameter: 2294 km (0. 18 Dearth) Mass: 1. 2 x 1025 g (0. 002 Mearth) Density: 1. 84 g/cm 3 Rotation Period: 6. 39 days o Tilt of Axis: 96 (retrograde!) o Surface Temperature: 43 K (-382 F)

Pluto Physical Data • • Orbital Semi-Major Axis: 39. 44 AU Orbital Period: 247. 7 years o Orbital Inclination: 17. 2 Orbital Eccentricity: 0. 250 Surface Gravity: 0. 06 Earth gravity Satellites: 1 Magnetic Field: unknown

The Discovery of Planet X • Discovered Feb 8, 1930 by then 24 -year old Clyde Tombaugh • Its existence was predicted by Percival Lowell using the same techniques that Leverrier used to find Neptune

The Discovery of Planet X January 23, 1930 January 29, 1930 The Plates on which Clyde Tombaugh found Pluto

Pluto’s Surface • This image was taken by the Hubble Space Telescope and is the best surface map yet made • Only contrasts are seen, no features • Pluto has not yet been visited by spacecraft

Pluto’s Atmosphere • • Very thin atmosphere (when closest to Sun) Envelopes its moon too Mostly made of Nitrogen and Methane Atmosphere condenses and snows to the surface of Pluto and its moon when they are farther from the Sun

Pluto’s Moon CHARON: • Discovered by James Christy in 1978 • Saw a bump move from one side of Pluto to the other about every six days • About half the size of Pluto, orbits retrograde One of Christy’s images

Pluto’s Moon • As seen by Hubble Space Telescope Charon Pluto 19, 700 km

Pluto’s Strange Orbit • Pluto’s Orbit is highly eccentric (0. 250), highly inclined to the plane of the solar o system (17. 2 ), and its orbit crosses Neptune’s! • Since Jan 23, 1979 and until March 15, 1999 Pluto is closer to the Sun the Neptune!

Pluto’s Orgin • Since Pluto and Charon are thought to have the same composition as Neptune’s Triton, it is suggested that they might be escaped satellites of Neptune (dynamicists say no) • Or Triton, Pluto and Charon all formed near Neptune and only Triton was captured

Asteroids

The Asteroid Belt Theory 1: • Material between Jupiter and Mars tried to form a planet when the Solar System was forming, but Jupiter’s gravitational influence wouldn’t let it happen Theory 2: • A planet did form between Jupiter and Mars (Asteroidia), and some catastrophic event destroyed the planet, leaving the asteroids

The Discovery of Asteroids • On the first day of the 19 th C. (Jan 1, 1801), Ceres (the largest known asteroid) was discovered by Giuseppe Piazzi • By the end of the 19 th C. , several hundred were known • We now know of more than 7000

Particular Asteroids CERES: • The largest asteroid by far • Diameter : 914 km • Contains 25% of the mass of all the asteroids combined The next largest are Pallas, Vesta, and Hygiea which are between 400 and 525 km in diameter All other known asteroids are less than 340 km across

Particular Asteroids IIDA and DACTYL: • Ida was encountered by the Galileo spacecraft in 1993 • Ida was found to have a small satellite, Dactyl • Dactyl’s size is 1. 6 x 1. 2 km, and orbits 90 km above Ida

Comets Comet West

Comet Basics • Comets are mostly (~50%) water ice • Comets are referred to as “dirty snowballs” • They are a mixture of water ice, frozen gases, and silicate materials • Comets have very eccentric orbits • They only have tails when close to the Sun • The tails are made of gas and dust released by the comet.

Anatomy of a Comet Direction of Comet’s Motion Ion Tail Coma Nucleus To Sun Hydrogen Cloud Dust Tail

History of Comets m

Comet Halley • Orbits Sun every 76 years • Furthest point in its orbit is just beyond the orbit of Neptune • Nucleus: 15 x 8 km • Rotates every 7. 6 days

Recent Comets Comet Hyakutake in March of 1996 Image taken by J. De Buizer and J. Radomski of the University of Florida Department of Astronomy

Recent Comets Comet Hale-Bopp in March 1997 Image taken by J. De. Buizer and J. Radomski of the University of Florida Department of Astronomy

Meteors, Meteorites, and Meteor Showers

Meteor Nomenclature Meteoroids - interplanetary debris Meteor - Also called “shooting star” When a meteorite has entered the atmosphere creating a streak of light Meteorite - Those few meteoroids that make it to the Earth’s surface

Types of Meteorites IRONS: • Mostly made of iron with about 9% nickel STONES: • Primarily silicates similar to Earth rocks STONY-IRONS: • Mixture of the above two types

Meteor Showers • Associated with debris left behind by comets • Typically very small meteoroids, so no meteorites are produced during a shower • Can be as many as 100 meteors per hour in a good shower

Meteor Impacts • One catastrophic meteor impact every 26 million years • Might have been responsible for dinosaur extinction Barringer crater in Arizona (1200 m in diameter, 200 m deep)

Zodiacal Light and Gegenschein • Zodiacal light is due to dust, concentrated in the plane of the solar system, that reflects the light of the Sun towards our eyes • Reflection from the dust also causes a patch of light Horizon directly opposite the Sun, called the gegenschein Ecliptic Zodiacal Light Sun