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 D earth ) Mass: 1.2x10 25 g (0.002 M earth ) Density: 2.03 g/cm 3 Rotation Period: 6.39 days Tilt of Axis: 96 o (retrograde!) Surface Temperature: 43 K (-382 o F)

Pluto Physical Data Orbital Semi-Major Axis: AU Orbital Period: years Orbital Inclination: 17.2 o Orbital Eccentricity: Surface Gravity: 0.06 Earth gravity Satellites: 3 known Magnetic Field: unknown

The Discovery of Planet X? Discovered Feb 8, 1930 by then 24-year old Clyde Tombaugh by coincidence. The existence of a planet X was predicted by Percival Lowell using the same techniques that Leverrier used to find Neptune – but turned out to be based on measurement noise.

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

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 but “New Horizons” is on the way. Stay tuned for Pluto’s surface is probably a methane and water ice mixture (1) covering a water ice mantle (2) with an ice/rock core (3).

Surfaces of Charon, Nix and Hydra This image was taken by the Hubble Space Telescope and is the best surface map yet made Only contrasts are seen, no features Charon’s surface is mostly water ice due to lower surface gravity. Nix and Hydra probably also have water ice surfaces Nix and Hydra discovered in 2005 by the Hubble Space Telescope's Pluto Companion Search Team

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 Named after the ferryman who rowed souls across the River Styx to Pluto's realm in the underworld of Greek and Roman mythology.

Pluto’s Moon As seen by Hubble Space Telescope 19,700 km Pluto Charon Density 2.03 g/cm 3 70% rock and 30% water ice much like Triton Density 1.65 g/cm 3

Pluto system to be visited by the New Horizons mission in Nix and hydra discovered in 2005 by the Hubble Space Telescope's Pluto Companion Search Team NOT picture. Best picture currently possible from the ground.

Possible formation of Charon Charon’s orbit within deg of Pluto’s equator supports this scenario.

Pluto’s Orbit not so Strange anymore? Pluto’s Orbit is highly eccentric (0.250), highly inclined to the plane of the solar system (17.2 o ), and its orbit crosses Neptune’s! From Jan 23, 1979 and until March 15,1999 Pluto was closer to the Sun than 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 as many other Kuiperbelt objects did and only Triton was captured

Many more Trans-Neptunian objects now discovered

Neptune’s satellite Triton Methane surface sprinkled by impact craters and geysers

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 19th C. (Jan 1,1801), Ceres (the largest known asteroid) was discovered by Giuseppe Piazzi By the end of the 19th C., several hundred were known We now know of more than 10,000

Particular Asteroids CERES: The largest asteroid by far Diameter : 914 km Contains 25% of the mass of all the asteroids combined. The water asteroid – having more water than the Earth Dawn to arrive at Ceres 2015, Vesta in 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 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 IIDA and DACTYL: Dactyl was blasted of Ida and will eventually fall back. Many asteroids were smashed-up and reassembled.

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 – because their orbits have been recently perturbed sending them much closer to the Sun. 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 Dust Tail Ion Tail Coma Direction of Comet’s Motion To Sun Nucleus Hydrogen Cloud

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 x 8 km Rotates every 7.6 days 1986 Halley mission – first picture of a comet nucleus

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

Iron Meteorite Lodged in Tree Trunk Meteorite interiors remain cold throughout atmospheric flight and can therefore preserve valuable information on how the solar system formed.

Some inclusions formed in an oxygen-rich environment and date to billion years old, while other chondrules were formed in an oxygen setting much like that on Earth and date to billion, or less, years old. Example of what we Learned Heat from Shock waves in gas … so gas was there Temp. [K]

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 on average Might have been responsible for dinosaur extinction Earth population of 7.6 billion means fatalities are. Watch out for statistics …. (compare 2004 Asian tsunami above 226,000 fatalities) Barringer crater in Arizona (1200 m in diameter, 200 m deep)

Impact frequency

Fatality Probability 2004 Tsunami

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 directly opposite the Sun, called the gegenschein Ecliptic Sun Horizon Zodiacal Light

Zodiacal Light and Gegenschein The zodiacal light in the eastern sky before the beginning of morning twilight. The planet Venus and the open cluster M44 are also visible in this photograph. Zodiacal Light