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General Astronomy The Solar System The Smaller Objects

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The Smaller Members The smaller members of the System are composed of the: Minor Planets (Asteroids) Comets Meteoroids Dust and Gas

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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: N(4+N)/10ObjectAU 00.4Mercury0.4 30.7Venus0.7 61.0Earth1.0 121.6Mars1.5 242.8 485.2Jupiter5.2 9610.0Saturn9.5 19219.6Uranus19.3 38439.0Neptune30.6 76877.2Pluto39.4 Known to Titus and Bode

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Asteroids.

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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

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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.

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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 9 About two dozen, have inclinations over 25 The distances lie in a range from 2.3 to 3.3 AU

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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 (Western) Trojans (Eastern) 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)

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Kirkwoods 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.

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Non-Belt Asteroids Apollo-Amor Objects: Not all asteroids orbit within the asteroid belt. Asteroids with elliptical orbits, reaching into the inner solar system. Some potentially colliding with Mars or Earth. Trojans: Sharing stable orbits along the orbit of Jupiter.

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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

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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

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433 Eros: Boulders and Craters The NEAR spacecraft in orbit

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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

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Ida and Dactyl Dactyl is the small "moon" orbiting asteroid Ida

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Exploring the Asteroids Dawn The Dawn spacecraft was launched September 27, 2007 Went into orbit around Vesta on July 17, 2011 Dawn left Vesta orbit on September 5, 2012 Currently Dawn is about 250 million miles from the Sun heading for Ceres (at over 40000 mph) Anticipated arrival time at Ceres is late March or early April of 2015

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Vesta

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A wall structure And Marcia crater

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Vesta Marcia crater

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When Dawn arrives (2015) at Ceres we should get much better views! Even more interesting, the signature of water has been detected. It is thought that icy plumes are emitted as parts of the surface are heated by the Sun Well know for sure when Dawn goes into orbit Next Stop: Ceres

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Comets

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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.

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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

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Structure 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'

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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 comets 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.

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Deep Impact The approach

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Deep Impact: The Collision

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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

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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.

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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

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Rosettas Mission Summer 2014, the Rosetta spacecraft intercepts and goes into orbit about comet 67P/ChuryumovGerasimenko at that time between the orbits of Mars and Jupiter after travelling for 10 years, 5 months and 4 days.

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Rosetta

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Philae as seen by Rosetta The first probe ever to land on the surface of a comet performed some serious science before going into hibernation. Philae lander found organic molecules in the comet's atmosphere and discovered that the frigid object's surface is as hard as ice. On Nov. 12, 2014, Philae became the first probe to softly land on the face of a comet. After being released from the orbiter, the lander actually bounced off Comet 67P/Churyumov-Gerasimenko twice before coming to its current less-than-ideal resting spot. Because of the low sunlight conditions, Philae went into hibernation after only about 57 hours on the comet when its battery depleted. Before shutdown, one of Philae's instruments managed to "sniff" the first organic molecules detected in the atmosphere of the comet scientists still aren't sure what kind of organics carbon-containing molecules that are the building blocks of life on Earth were found.

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Philaes Final resting place (in the shadows)

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Rosetta and Philae Rosetta spacecraft captured these images of Philaes bouncing landing during its historic touchdown on Nov. 12, 2014

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The Tail Gas Tail Ionized Gases Blue emitted light Dust Tail Sand & dirt White reflected light Jets Gas pockets breaking through the crust

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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 suns radiation pressure. Lagging behind the comet along its trajectory

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Gas and Dust Tails of Comet Mrkos in 1957

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Comet Hale- Bopp in 1997

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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 Earths moon and on Jupiters moon Callisto may have been caused by fragments of a comet.

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Fragmenting Comets Comet Linear apparently completely vaporized during its sun passage in 2000. Only small rocky fragments remained.

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Comet Orbits

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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

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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)

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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.

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Image from JPL

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The BIG Picture

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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.

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Chunks of rock and iron floating in space, their name reflects where they are found: Meteoroid In space Meteor In the Sky Meteorite On the ground Bolides (Fireball)

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Meteorites Meteorites come in several flavors: 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. Their sizes range from dust to grains of sand to the size of houses

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Meteor Showers As Earths 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: Midnight Dawn

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Meteor Showers Most meteors appear in showers, peaking periodically at specific dates of the year.

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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.

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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

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The Leonid Meteor Shower in 2002

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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

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Earth's Known Impact Craters

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1992 Peekskill Fall On October 9, 1992, a fireball was seen streaking across the sky from Kentucky to New York.

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1992 Peekskill, NY

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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.

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Wabar, Saudi Arabia (0.072mi)

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Wolfe Creek, Australia Wolfe Creek, Australia (0.55mi)

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Barringer Crater, Arizona (0.75 mi) It is estimated that the meteorite that produced the Barringer Crater was still traveling at 11 km/second when it struck what is now the Arizona desert 49,000 years ago.

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Roter Kamm, Namibia (1.6mi)

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Brent, Canada (2.4 mi)

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Spider, Australia (8.1mi)

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Manicouagan, Canada (62mi)

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Popigai, Russia (62 mi)

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Vredefort, South Africa (125-185mi)

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Tunguska, Siberia 1908

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Chesapeake Crater, VA Marine impact event, about 35 Myr old, with typical inverted sombrero shape due to multi- layer nature of target region: soft sediments + hard rock Its existence explains several geological features of the area including the saline groundwater and higher rate of subsidence at the mouth of the Chesapeake Bay. Inner basin (the head of the sombrero) is about 25 miles wide - Outer basin (the brim of the sombrero) extends to about 53 miles.

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Mystery Structure #1

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Gosses Bluff Crater, Australia Complex crater with a central peak ring (143 million years old) Crater diameter: 22 km Mostly eroded away only spotted by the different color of the vegetation Inner ring: 5 km Round bluff that is fairly easy to spot.

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Mystery structure #2

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Aorounga crater, Chad Complex crater with a central peak ring Crater diameter: 12.6 km Buried under rocks and sand for a long time, it has been uncovered again by recent erosion. Possible crater Aorounga may be part of a crater chain

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Mystery structure #3

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Clearwater, Canada two craters, both 290 Million years ago Clearwater West: 22.5 miles Complex structure Clearwater East: 16 miles Probably they were made by a double asteroid, like Toutatis

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Mystery structure #4

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Chicxulub Structure, Mexico 65 Myr old (end of dinosaurs!) Structure diameter: 106 miles Crater is not really visible at the surface

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Dino Killer? A large body of scientific evidence now exists that support the hypothesis that a major asteroid or comet impact occurred in the Caribbean region at the boundary of the Cretaceous and Tertiary periods in Earth's geologic history. Artist: Don Davis Such an impact is suspected to be responsible for the mass extinction of many floral and faunal species, including the large dinosaurs, that marked the end of the Cretaceous period. Until now, the remains of such an impact crater have escaped detection. The Cenote Ring off Yucatan represents a prime candidate for the impact site of a global catastrophic event.

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Evidence for Chicxulub In 1980, Nobel laureate Luis Alvarez, his geologist son Walter Alvarez, nuclear chemist Frank Asaro, and paleontologist Helen Michael published on their discovery of high levels of the element Iridium in a clay layer separating marine sediments of Cretaceous and Tertiary age. The thin clay layer that marks the boundary between the Cretaceous and Tertiary rocks. This layer has been found at many localities around the Earth. (Courtesy of Canadian Museum of Nature, Ottawa)

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This three-dimensional map of local gravity and magnetic field variations shows a multi-ringed structure called Chicxulub named after a village located near its center. The impact basin is buried by several hundred meters of sediment, hiding it from view. This image shows the basin viewed obliquely from approximately 60 above the surface looking north, with artificial lighting from the south. (Courtesy of V. L. Sharpton, LPI) Chicxulub, Yucatan Peninsula, Mexico This leads to the idea of a mass extinction at the K-T boundary by the impact of an asteroid (~10 Km diameter). The crater that remains is about 150 300 Km diameter. No land animal > 25 Kg survived.

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Earth Impact?

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Earth's Recent 2 nd Moon 2006 RH 120 was discovered on 14 September 2006 by the 27-inch Schmidt camera of the Catalina Sky Survey. Preliminary orbital calculations indicated it was captured by Earth's gravity Analysis shows the body must be a dense rocky body or at least regularly shaped. One hypothesis is that the object is a piece of lunar rock ejected by an impact. However, the object was later confirmed to be minor planet. The object made four Earth orbits before being ejected after the June 2007 perigee. At that perigee, it dipped inside the Moon's orbit to a distance of approximately 200,000 miles. Douglas R. Allen, Dordt College