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Small Bodies & the Origin of the Solar System
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Unused Spare Parts
• Comets, asteroids, and meteors are the unused leftovers from the formation of the solar system.
• Their chemical compositions and distribution yield clues as to how the solar system formed.
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Asteroids – rocky leftovers of the inner solar system
• Location
– Asteroid Belt
– Trojan or Lagrange Asteroids
– Random Orbits
• Types of Asteroids
• Minor planets
• NEO’s
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Asteroid belt
• Generally, just outside Mars’ orbit
• 2.7 A.U. average distance
• Total mass of all asteroids is <5% of the earth’s mass (2 to 4 of our moons.)
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Lagrange Asteroids
• Clusters of asteroids co-orbit with the gas giant planets, 60o ahead and 60o behind the positions of the planets.
• The clusters are centered on the L4 and L5 Lagrange points (points in space where Jupiter’s gravitational influence equals the sun’s gravitation.)
• Jupiter’s Lagrange asteroids are known as the Trojan asteroids.
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Types of Asteroids
• S – Stony
• C – Carbonaceous (modified stony asteroids with dark surfaces and interiors)
• M – Metallic (comparatively rare)
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Gaspra – a typical stony asteroid
Stony Asteroids
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Some asteroids are thought to be rubblepiles held together by very low gravity.
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Major Asteroids or Dwarf Planets?
• Over 200 objects have diameters of >100 km.
• Ceres – largest, the size of Texas (1030 km). Named after the Roman goddess of the harvest (cereal). Recently named a dwarf planet.
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Rotation of Ceres Best Model
We don’tknow whatthe whitespot is yet.
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Major Asteroids
• Vesta – smaller (450 km diameter), but much brighter. Barely visible to naked eye.
• Movie of Vesta’s rotation.http://atropos.as.arizona.edu/aiz/teaching/nats102/images/Vesta.mpg
• Pallas• Juno
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Vesta shows signs of having been moltenat one point in its history.
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NEO’s (Near Earth Objects)and PHA’s (Potentially Hazardous
Asteroids)• Hundreds of asteroids cross
earth’s orbit !
• Several have approached within 600,000 km of earth (2 times moon’s orbital distance)
• Collisions with Earth have occurred in the past
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•Barringer Crater in Arizona – from an impact
within the last 50,000 to 100,000 years
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•This asteroid has its own little moon !
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•Toutatis – one of the closest !
Toutatis spins on 2 axes.
5 km long. Passed just 29 lunar distancesfrom the earth in 2000. 19
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Mission to Asteroids
• Deep Space 1 flew by asteroid 1992 KD Braille in 1999.
• N.E.A.R. took close-up photos of, then landed on asteroid Eros, Feb. 12, 2001.
• JAXA Hayabusa visited asteroid Itokawa in 2005. It had a small lander which should have landed on the asteroid, but malfunctioned.
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NEAR “landing” on Eros.
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Hayabusa - ion propulsion - autonomous navigation - sample return
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Comets – outer S.S. messengers
• Structure• Orbits & Types• Oort Cloud vs. Kuiper Belt• Famous Comets• What message do they convey?
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Structure
• Nucleus– Water ice, frozen CO2, N2, methane,
ammonia, HCN, (CN)2 (cyanogen), amino acids, sugars all detected.
– Embedded with rocks and dust– Extremely dark, tarry surface.
• Coma– Envelope of water vapor and H2 around
nucleus25
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Structure (2)
• Ion tail – ionized gas pushed directly away from the sun by solar wind.
• Dust tail – heavier particles that follow along behind the path of the comet.– The dusty path of a comet lingers for
decades, even centuries. When the earth passes through the dusty path again later, a meteor shower is produced.
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StructureDirty Snowballs
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Sunlight causes
jets of gas to
spew from
the comet’s
nucleus. This
creates the
coma.
Jets of gas
•Dark, tarry organic coating
Photo by
Giotto spacecraft
(ESA)
Nucleus of Halley’s Comet
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Nucleus of Borrelly
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•Ion or plasma tail•Dust tail
•Direction of comet’s movement
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Comet Origins & Orbits
• Kuiper Belt
– Short period comets (return <200 yrs)
– 50 to 200 A.U.
– Several billion comets
– Cometary orbits are more often near the ecliptic, but may be prograde or retrograde.
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Comet Origins & Orbits (2)
• Oort Cloud
– Long period comets (return >200 years or may only pass by sun once)
– Spherical shell of matter up to 2 light years (65,000 A.U.) in radius.
– Trillions of comets
– Comets may come in from any direction, with prograde or retrograde orbits.
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Famous Comets
• Halley (1984)
• Hale Bopp (’96)
• Hyakutake (’94)
• Shoemaker-Levy 9 (‘94)
• Kohoutek (’75)
• West (‘75)
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Halley’s comet1986
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Halley’s Comet Orbit
•Many comets have retrograde orbits38
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Comet Shoemaker-Levy 9 broke into aseries of fragments before impactingJupiter.
The ‘fireball’from eachimpact waslarger thanthe earth.
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An atmospheric “scar” left by the impactof Shoemaker-Levy 9. These faded afterseveral weeks.
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Comet Hale Bopp, 2002
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CometSwanhas beenvisiblein oursky thepast fewweeks.
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Past Missions to Comets
• There have been 11 past missions to comets, with 2 current missions.
• Giotto – examined Halley’s comet in 1986. Photographed the nucleus from a distance of only 200 km, then continued on to comet Grigg-Skellerup in 1992.
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Past Missions to Comets (2)
• Deep Impact – launched a 350 kg copper impactor into the nucleus of comet 9P/Tempel 1, in July, 2005.
– A 100 m x 25 m crater was created.
• Visible and infrared spectrometers on the parent craft looked for the composition of the nucleus.– 250,000 kg of water vapor were detected.
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Current Missions to Comets
• Stardust – sampled the coma of P Wild 2 from a distance of 236 km above the nucleus.
• Returned comet particles back to the earth for microscopic examination and chemical testing.
You can help with the microscopic work bysigning up at the following website.http://stardust.jpl.nasa.gov/home/index.html
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Stardust inside comet Wild’s coma.
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Comet particlestrapped in theaerogel (a lightsilicon gel).
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5151
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Current Missions to Comets (2)
• Rosetta – launched 2004 to comet 67P/Churyumov-Gerasimenko. Rosetta will fly along with the comet for 2 years as it approaches the sun, beginning in 2014. It also has a small lander which will explore the comet’s nucleus.
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Formation of the solar system
• Accretion from a nebula of gas and dust.
• Spinning nebula flattens to a disk• Different materials condense at
different distances from the sun (temperature gradient).
• Other solar systems may be quite different from ours.
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•A rotating cloud of gas & dust
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•Rotation causes the nebula to flatten
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•A star ignites in the center and a
temperature gradient forms.
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•Solids condense close to the star
•Volatiles & ices condense farther out
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We’re unsure of our model
• Solar systems that we’ve observed around other stars are quite different from ours.
– Planets Jupiter-sized and larger have been observed orbiting at Mercury-like distances from their stars.
– Do gas giants form closer to the star and then migrate outward, or vice versa?
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http://www.newscientist.com/data/images/ns/cms/dn8259/dn8259-3_506.jpghttp://www.fli-cam.com/images/comet-liner.jpghttp://www.nasa.gov/images/content/116911main_spitzer-comet-060205-browse.jpghttp://galileo.rice.edu/images/things/comet_1532_apian-l.gifhttp://www.astrocentral.co.uk/comet_diagram.gifhttp://www.solarviews.com/thumb/comet/comet.gifhttp://physics.uoregon.edu/~jimbrau/BrauImNew/Chap14/FG14_06.jpghttp://www.mallorcaweb.net/masm/Aster/astervarios.JPGhttp://en.wikipedia.org/wiki/Image:Ceres_Rotation.jpghttp://near.jhuapl.edu/http://www.isas.jaxa.jp/e/enterp/missions/hayabusa/index.shtmlhttp://www.daviddarling.info/encyclopedia/N/NEAR.htmlhttp://www.nasa.gov/worldbook/comet_worldbook.htmlhttp://herschel.jpl.nasa.gov/images/kuiper_oort.jpghttp://www2.jpl.nasa.gov/sl9/gif/sl9hst.gifhttp://bluepoint.gen.tr/sagan/sholevy9.gifhttp://nssdc.gsfc.nasa.gov/planetary/sl9/image/sl9g_hst5.gifhttp://www.magma.ca/http://www.spaceweather.com/swpod2006/25oct06/lawrence.jpghttp://solarsystem.nasa.gov/missions/profile.cfmhttp://www.hour25online.com/pix/comet-tempel1-orbit_01a.jpghttp://www.cfa.harvard.edu/press/Deep-Impact_lores.jpg
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http://deepimpact.jpl.nasa.gov/gallery/jpg/HRI_937_1.jpghttp://stardust.jpl.nasa.gov/images/gallery/Wild2Encounter2.jpghttp://stardust.jpl.nasa.gov/images/gallery/aerogel_tracks.jpghttp://stardust.jpl.nasa.gov/images/gallery/aerogelhand.jpghttp://boojum.as.arizona.edu/~jill/NS102_2006/Lectures/Lecture6/09-13.jpg
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Meteoroids – asteroids on a collision course…with us!
• Meteor – the trail of light & ionized gas left by a meteoroid
• Meteorite – what’s left of a meteoroid that hits the Earth.
• Bolide – a fireball or especially bright meteor.
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Types of Meteorites
• Types – just like asteroids!– stony (incl. carbonaceous
chondrites) – irons & iron / nickel (90% / 10%)– stony-irons (a combination of
materials)– the type of meteorite tells you
where it came from.
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•A stony meteorite (hard to find)
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•An iron meteorite (easier to find)
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•A carbonaceous chondrite
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Meteoroids were formed in parent bodies (planetessimals)
• Stonies were formed in the:
mantle• Irons were formed in the:
core
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Meteoroids – early planet stuff
• Meteoroids come from the earliest condensed stuff in the solar system. They give us the chemical composition of the earliest planetissimals.
• Most are about 4.6+ billion years old.
