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Asteroids and Meteorites
Asteroid Facts
• Asteroids are rocky le2overs of planet forma7on. • Asteroids are cratered and not round. • The largest is Ceres, diameter ~1000 kilometers. • 150,000 in catalogs, and probably over a million with
diameter >1 kilometer. • Small asteroids are more common than large asteroids. • All the asteroids in the solar system wouldn’t add up to
even a small terrestrial planet.
Asteroids with Moons
• Some large asteroids have their own moon.
• Asteroid Ida has a 7ny moon named Dactyl.
Asteroid Orbits
• Most asteroids orbit in the asteroid belt between Mars and Jupiter.
• Trojan asteroids follow Jupiter’s orbit.
• Orbits of near-‐Earth asteroids cross Earth’s orbit.
Origin of Asteroid Belt
• Rocky planetesimals between Mars and Jupiter did not accrete into a planet.
• Jupiter’s gravity, through influence of orbital resonances, s7rred up asteroid orbits and prevented their accre7on into a planet.
If you discover an asteroid and track its orbit, you get to name it.
Meteorites
Meteor Terminology
• Meteorite: a rock from space that falls through Earth’s atmosphere
• Meteor: the bright trail le2 by a meteorite
• Falling star = meteor
• Bolide = a really bright meteor
Near Earth Asteroids
Meteorite Impact
Chicago, March 26, 2003
Meteorite Types
1) Primi7ve: unchanged in composi7on since they first formed 4.6 billion years ago
2) Processed: younger; have experienced processes like volcanism or differen7a7on
3) Stony Meteorites; Iron Meteorites
Stony Meteorite
Iron Meteorite
Meteorites from Moon and Mars
• A few meteorites arrive from the Moon and Mars.
• Composi7on differs from the asteroid fragments.
• A cheap (but slow) way to acquire Moon rocks and Mars rocks
Collec7ng meteorites in Antarc7ca and other places…
Robert A Haag has flown ultralight plane over Sonoran Desert Looking for black rocks.
Finding meteorites in Antarc7ca is big science business.
Meteor Showers
• Many meteors seeming to come in along radiants
Meteors in a meteor shower appear to emanate from the same area of sky because of Earth’s mo7on through space.
Tek7tes Glassy fragments, Probably formed by impacts
Impacts and Mass Ex7nc7ons
K-‐T Boundary • K-‐T Boundary (Cretaceous-‐Ter7ary)
• There is an excess of iridium everywhere on the Earth at the layer which was laid down 65 million years ago.
• Iridium is rare on Earth, but is common in certain types of meteorites.
• 65 million years ago, there was a mass ex7nc7on, 75-‐80% of all species died suddenly, including the dinosaurs, pterosaurs, ammonites and most marine rep7les
• A large impact killed the dinosaurs
Other Mass Ex7nc7ons
At least 5 other mass ex7nc7ons in the fossil record
Largest was at the end of the Permian Period, 245 million years ago, when over 96% of the species alive at the 7me became ex7nct.
There is no evidence for a meteor impact causing any of the other mass ex7nc7ons
Should we worry? Es7mate that the odds that you will die from an impact of an asteroid in any given year is about 1 in 20,000
NASA has funded several searches for NEAs
Cause Odds of Dying in the US
Motor Vehicle accident 1 in 100
Murder 1 in 300
Fire 1 in 800
Firearms Accident 1 in 2,500
Electrocu7on 1 in 5,000
Asteroid impact 1 in 20,000
Airplane Crash 1 in 20,000
Flood 1 in 30,000
Tornado 1 in 60,000
Venomous Bite or S7ng 1 in 100,000
Pluto and Charon Kuiper Belt and Comets
Discovery of Pluto
• Pluto was discovered in 1930 by Clyde Tombaugh (1906 – 1997)
• Irregulari7es in the orbit of Uranus and Neptune lead to predic7ons of a 9th planet
• The calcula7ons were in error, but Tombaugh discovered Pluto anyway
• Discovery was at Lowell Observatory in Flagstaff, AZ
Tombaugh built his own telescope in 1926, at age 20 Sent his drawings to the professional astronomers at Lowell Observatory They hired him to search for Pluto
In 1932 he went to college at the University of Kansas, received his B.S.
During WWII he served in the Navy and Taught naviga7on
A2er the War, Lowell didn’t have enough money to hire Tombaugh so he went to work for the military at the ballis7cs research labs at the White Sands Missile Range in Las Cruces, New Mexico, where he worked Un7l 1973.
Pluto’s Moons: Charon and others • In 1978, it was discovered that Pluto has a moon, given the name
Charon, a2er the ferryman who ferries dead souls to the underworld, where they enter the realm of Pluto, the roman god of the underworld
• Pluto: diameter = 2300 km • Charon diameter = 1200 km • Pluto-‐Charon distance = 20,000 km, half the circumference of the Earth
What is Pluto like?
• Its moon Charon is nearly as large as Pluto itself (probably made by a major impact).
• Pluto is very cold (40 K). • Pluto has a thin nitrogen atmosphere that will refreeze onto the surface as Pluto’s orbit takes it farther from the Sun.
Hubble’s View of Pluto and Its Moons
Pluto’s Orbit – 248 Earth years
• Pluto will never hit Neptune, even though their orbits cross, because of their 3:2 orbital resonance.
• Neptune orbits three 7mes during the 7me Pluto orbits twice.
Is Pluto a Planet?
• Much smaller than the terrestrial or jovian planets • Not a gas giant like other outer planets • Has an icy composi7on like a comet • Has a very ellip7cal, inclined orbit • Has more in common with comets and Kuiper Belt Objects than with the eight major planets
• But it is spherical, has an atmosphere, and has moons.
Other Icy Bodies
• There are many icy objects like Pluto on ellip7cal, inclined orbits beyond Neptune.
• The largest of these, Eris, was discovered in summer 2005, and is even larger than Pluto.
Kuiper Belt Objects
• These large, icy objects have orbits similar to the smaller objects in the Kuiper belt that become comets.
• So are they very large comets or very small planets?
Other Kuiper Belt Objects
• Most have been discovered very recently so liqle is known about them.
• NASA’s New Horizons mission will study Pluto and a few other Kuiper belt object in a planned flyby.
• Launched in 2006, will arrive at Pluto in 2015
Comets
Comet Facts
• Formed beyond the frost line, comets are icy counterparts to asteroids.
• Nucleus of comet is a “dirty snowball.” • Most comets do not have tails. • Most comets remain perpetually frozen in the outer solar system.
• Only comets that enter the inner solar system grow tails.
Sun-‐Grazing Comet
Nucleus of Comet
• A “dirty snowball”
• Source of material for comet’s tail
Deep Impact
• Mission to study nucleus of Comet Tempel 1
• Projec7le hit surface on July 4, 2005.
• Many telescopes studied a2ermath of impact.
Anatomy of a Comet
• A coma is the atmosphere that comes from a comet’s heated nucleus.
• A plasma tail is gas escaping from coma, pushed by the solar wind.
• A dust tail is pushed by photons.
Growth of Tail
Comets eject small par7cles that follow the comet around in its orbit and cause meteor showers when Earth crosses the comet’s orbit.
Where do comets come from?
Kuiper belt: on orderly orbits from 30–100 AU in disk of solar system
Oort cloud: on random orbits extending to about 50,000 AU
Only a 7ny number of comets enter the inner solar system. Most stay far from the Sun.
How did they get there?
• Kuiper belt comets formed in the Kuiper belt: flat plane, aligned with the plane of planetary orbits, orbi7ng in the same direc7on as the planets
• Oort cloud comets were once closer to the Sun, but they were kicked out there by gravita7onal interac7ons with jovian planets: spherical distribu7on, orbits in any direc7on
Halley’s Comet
• Most comets come near the Sun once and then are destroyed
• A few are “periodic” – Halley’s Comet comes by once every 75 years
• Last 7me: 1986 • First 7me recorded: 240 BC • Edmund Halley (pal of Isaac Newton) described orbit in 1705
• Appeared in 1066 (omen for Baqle of the Has7ngs)
• King Harold cowers a2er seeing Halley’s comet • Depic7on in the Bayeux Tapestries, 1070s • See panorama on Wikipedia
