General Astronomy The Solar System The Smaller Objects
The Smaller Members The smaller members of the System are composed of the: Minor Planets (Asteroids) Comets Meteoroids Dust and Gas
Titus-Bode "Law" In 1766, Johann Titus notices a peculiar pattern in the distances to the known planets; in 1772, Bode brings it into prominence: Known to Titus and Bode
Asteroids • The discovery of Uranus in 1781 was found to fit nicely into "Bode's Law" • A search for the 'missing planet' was organized since nothing at 2.8AU had been found • On January 1, 1801, Piazzi (a Sicilian astronomer) noted a new object which he watched until February 11. He wrote Bode of his discovery, but by the time Bode looked for it, the object was too near the direction of the Sun for observation. • In November, Gauss predicted the location of this object based on Piazzi's observations; it was found on Dec 31, 1801 • Piazzi named the object "Ceres" after the protecting goddess of Sicily • The missing planet had been found at a distance of 2.77 AU
Asteroids • It came as a surprise, when Olbers found another, Pallas, in March 1802 • In short succession, came the discoveries of: • Juno (1804) • Vesta (1807) • By 1890, more than 300 'planets' had been found. All where Bode's "Law" said one should be located.
Asteroids Orbits • Most minor planets, or asteroids, orbit the sun in the same direction as the rest of the system • Most are reasonably close to lying in the ecliptic plane • The average inclination is 9½° • About two dozen, have inclinations over 25° • The distances lie in a range from 2.3 to 3.3 AU
Lagrangian Points • In 1772, Lagrange realize that there were two peculiar point in Jupiter's orbit where the balancing of forces would permit asteroids to remain indefinitely: Jupiter Trojans (Eastern) Trojans (Western) 60° 60° * These are named after Homeric heroes. The custom is to name the eastern group after Greeks and the western group after the Trojans. (This custom began after several names had been assigned; so there is one Greek spy in the Trojan group and one Trojan spy in the Greek group)
Kirkwood’s Gaps The asteroid orbits are not evenly distributed throughout the asteroid belt between Mars and Jupiter. There are several gaps where no asteroids are found These correspond to resonances of the orbits with the orbit of Jupiter.
Non-Belt Asteroids Not all asteroids orbit within the asteroid belt. Apollo-Amor Objects: Trojans:Sharing stable orbits along the orbit of Jupiter. Asteroids with elliptical orbits, reaching into the inner solar system. Some potentially colliding with Mars or Earth.
Asteroid Names Once a minor planet is discovered and found to make at least one orbit about the Sun, it is given both a name and a number. The number is the next value in the sequence of discovery; the name is left to the discoverer: 1 Ceres 2 Pallas 433 Eros 1566 Icarus
433 Eros Mission to another world The NEAR spacecraft was sent to the asteroid 433 Eros. It arrived and went into orbit and was eventually landed on the asteroid. 433 Eros is an airless, irregular rock
433 Eros: Boulders and Craters • The NEAR spacecraft in orbit
433 Eros: Touchdown • At a height of 123 meters, this photo spans 6 meters. The rock at the top is about 4 meters across. • The bottom is where the transmission ended as the spacecraft landed on the asteroid on 12 FEB 2001
Ida and Dactyl Dactyl is the small "moon" orbiting asteroid Ida
Comets Comets were once thought to bring tidings of bad fortune. It was, for King Harald, when Halley's comet appeared in 1066 and he lost the English throne to William of Normandy. The ancient Chinese named them 'Broom Stars' In any event, they are beautiful and spectacular visitors to our night sky.
Structure The current model of a comet is known as the Dirty Snowball Model Comets are composed of: • Nucleus • Coma • Hydrogen Cloud • Tail • Ion Tail • Dust Tail • Jets
The Nucleus is ice, dirt and Frozen gases – a Slush ball! As the heat of the Sun warms the comet, the Hydrogen Cloud forms More warmth and the Coma makes the comet 'fuzzy' Structure
Deep Impact In December 2004, a Delta II rocket launched the combined Deep Impact spacecraft which left Earth's orbit toward the comet. In early July 2005, 24 hours before impact, the flyby spacecraft pointed high-precision tracking telescopes at the comet and released the impactor on a course to hit the comet's sunlit side. The impactor is a battery-powered spacecraft that operates independently of the flyby spacecraft for just one day. It is called a "smart" impactor because, after its release, it takes over its own navigation and maneuvers into the path of the comet. A camera on the impactor captures and relays images of the comet's nucleus just seconds before collision. The impact is not forceful enough to make an appreciable change in the comet's orbital path around the Sun. After release of the impactor, the flyby spacecraft maneuvered to a new path that, at closest approach passes 500 km (300 miles) from the comet. The flyby spacecraft observed and recorded the impact, the ejected material blasted from the crater, and the structure and composition of the crater's interior. After its shields protected it from the comet’s dust tail passing overhead, the flyby spacecraft turned to look at the comet again. The flyby spacecraft took additional data from the other side of the nucleus and observed changes in the comet's activity. While the flyby spacecraft and impactor did their jobs, professional and amateur astronomers at both large and small telescopes on Earth observed the impact and its aftermath.
Preliminary Findings • Comet Temple I has a very fluffy structure – weaker than a bank of powder snow • Distinct layers with impact craters and topography • Much carbon-containing molecules – substantial amount of organic molecules • Very porous – provides a good heat insulator for the core • Considerable water present
What are good little comets made of? These "comet soup" ingredients are pictured above: (in the back from left to right) a cup of ice and a cup of dry ice; (in measuring cups in the middle row from left to right) olivine, smectite clay, polycyclic aromatic hydrocarbons, spinel, metallic iron; (in the front row from left to right) the silicate enstatite, the carbonate dolomite, and the iron sulfide marcasite. Materials are courtesy of Dr. George Rossman of the California Institute of Technology's Geology and Planetary Sciences department.
The Nucleus This is the nucleus of Halley's Comet as seen by the Hubble Space Telescope It is a chunk of ice and sand grains and other frozen gases
The Tail • Gas Tail • Ionized Gases • Blue emitted light • Dust Tail • Sand & dirt • White reflected light • Jets • Gas pockets breaking through the crust
0 Two Types of Tails Ion tail: Ionized gas pushed away from the comet by the solar wind. Pointing straight away from the sun. Dust tail: Dust set free from vaporizing ice in the comet; carried away from the comet by the sun’s radiation pressure. Lagging behind the comet along its trajectory
0 Gas and Dust Tails of Comet Mrkos in 1957
0 Comet Hale-Bopp in 1997
Fragmentation of Comet Nuclei Comet nuclei are very fragile and are easily fragmented. Comet Shoemaker-Levy was disrupted by tidal forces of Jupiter Two chains of impact craters on Earth’s moon and on Jupiter’s moon Callisto may have been caused by fragments of a comet.
Fragmenting Comets Comet Linear apparently completely vaporized during its sun passage in 2000. Only small rocky fragments remained.
Comet Types • Short Period Comets • Periodic, returning in less than 200 years • Mostly orbit in the same direction as the rest of the Solar System objects • Tend to be in or near the ecliptic plane • Long Period Comets • May not be periodic (or have such a long period that it takes thousands of years to orbit. • May come from any angle to the ecliptic • May have any direction
Kuiper Belt • The short-period comets appear to share the ecliptic plane and the general direction of motion. • Their origin is in a belt about 30-50AU • The numbers of icy-bodies (comets) are estimated to be in the millions. • If nudged by Neptune's gravity, some are occasionally moved from their orbits and sent toward the Sun • Many astronomers now consider Pluto to be "just another" KBO (Kuiper Belt Object)
Oort Cloud • The long-period comets can come from any direction and at any angle. This suggest that their origin is spherically-distributed about the sun. • Their origin is now considered to be in a cloud, or shell, about the Sun at a distance of about 50,000 AU • Their numbers are estimated to be in the billions.
Meteors "I would more easily believe that two Yankee professors would lie than that stones would fall from heaven" - Supposedly said by Thomas Jefferson after hearing of meteorite exploding over Weston, Connecticut on December 14, 1807.
Chunks of rock and iron floating in space, their name reflects where they are found: • Meteoroid • In space • Meteor • In the Sky • Bolides • (Fireball) • Meteorite • On the ground
Stony meteorites are commonly made of familiar minerals like plagioclase, pyroxene, and olivine. It is believed that they were formed in the outer parts of asteroid belt. Stony meteorites look a lot like Earth rocks, and are often not recognized as meteorites. Their outer surfaces are usually melted as they pass through our atmosphere, giving them dark "fusion crusts." Iron meteorites are made almost entirely of iron metal with some nickel. As with stony meteorites, iron meteorites also have fusion crusts and show distinct molten metal shapes and flow markings Some meteorites are mixtures of iron and fragments of rock; they are called stony-iron meteorites. Probably formed at the boundary between the metal core and the rocky mantle of an asteroid. Meteorites Their sizes range from dust to grains of sand to the size of houses Meteorites come in several flavors:
Dawn Midnight Meteor Showers • As Earth’s on its orbit intersects the dust trail of a comet, we observe meteor showers (or sometimes storms) • These appear to radiate outward from a given constellation (the radiant) and are named accordingly. For example, the Leonides. • The best time to see them is after midnight:
Meteor Showers Most meteors appear in showers, peaking periodically at specific dates of the year.
0 Meteoroid Orbits Meteoroids contributing to a meteor shower are debris particles, orbiting in the path of a comet. Spread out all along the orbit of the comet. Comet may still exist or have been destroyed. Only few sporadic meteors are not associated with comet orbits.
Radiants of Meteor Showers Tracing the tracks of meteors in a shower backwards, they appear to come from a common origin, the radiant. ↔ Common direction of motion through space. The Perseid Meteor Shower
Earth Impacts Earth retains the poorest record of impact craters amongst terrestrial planets Why? • Plate tectonics • Erosion • Sedimentation • Life • Oceans are relatively young and hard to explore • Many impact structures are covered by younger sediments, others are highly eroded or heavily modified by erosion. • Few impact craters are well preserved on the surface There are about 160 known impact craters
1992 Peekskill Fall On October 9, 1992, a fireball was seen streaking across the sky from Kentucky to New York.
Chicago/Trinity Park, IL Sunday, March 30, 2003 Colby Navarro was sitting in her computer room about midnight Thursday, chatting on the phone with a friend, when she heard a boom that sent plaster shards from her ceiling falling to her carpeted floor. "It scared the living daylights out of me for sure," said Navarro. "I first thought a gunshot went off and ducked to the ground, but then I saw the 4- to 5-inch diameter hole in my ceiling. Then there was a burning smell." What crashed through Navarro's ceiling was a meteorite about the size of a grapefruit that landed less than 2 feet from where she was sitting. She touched it. It was warm and smoking and smelled like fireworks.