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