Solar System Debris Material leftover from the formation of the Solar System Gives important clues about its origin Composition: Asteroids and Meteoroids: rock and iron Comets: ice and dust The basic building blocks of planets! Asteroids Large rocky debris orbiting the Sun Discovering Asteroids Ceres, the largest asteroid Recently reclassified as a Dwarf Planet! 1
Discoverers of asteroids can name them! Subject to approval by the International Astronomical Union (IAU) Some Interesting Asteroid Names 4147 Lennon 4148 McCartney 4149 Harrison 4150 Starr 4305 Clapton 12818 Tomhanks 12820 Robinwilliams 13070 Seanconnery 13681 Monty Python The Asteroid Belt The asteroid belt does not look like this! Volume of the asteroid belt is so large that the average spacing a several million km! The Kirkwood Gaps The Trojan Asteroids of Jupiter Caused by orbital resonances! 2
Other Asteroid Families Planet-crossing Asteroids Armor Asteroids: cross the orbit of Mars Apollo Asteroids: cross the orbit of Earth Aten Asteroids: found within the orbit of Earth Can collide with the inner planets! Asteroid Collisions Asteroid Size Distribution Large asteroids are rare! Near Earth Asteroids Projects Attempting to locate all asteroids that could potentially hit the Earth There are currently 1167 Potentially Hazardous Asteroids (Nov 2010) 3
The Asteroid 1999 RQ36 is 560 m in diameter and has a 5.4 x 10-4 probability of hitting the Earth in 2182. How would this threat be classified on the Torino scale? Recent Impacts Meteor Crater, AZ This 1 km diameter crater was formed when a 10 m sized object hit the Arizona desert around 50,000 years ago. Tunguska Impact 30 m object exploded above the ground in over Siberia in 1908. No impact crater formed, although trees were flattened and set on fire for 100 s of km 4
Noctilucent Clouds Explanation 76-85 km Noctilucent Clouds after Shuttle Launches What was the Tunguska object? Noctilucent clouds were also seen for many days after the Tunguska impact This evidence suggests the object was an icy comet rather than a rocky meteoroid This is also consistent with the object exploding above ground as ice is easier to disintegrate Formed from water vapor produced during launch The Dinosaurs Appeared 245 mya during Triassic Period The K-T Boundary Suddenly became extinct 65 mya! Layer of soot 65 my old Rich in rare earth element Iridium (Ir) 5
The Impact Hypothesis Impact of 10 km asteroid 65 mya Effects of the Impact the asteroid hit the Earth with a force of 100 million hydrogen bombs a shower of red-hot debris was blasted up into the atmosphere and then settled down on the continents igniting massive wildfires huge tsunamis formed which flooded surrounding land more than 1000 km inland debris remained suspended in the atmosphere for months, blocking sunlight and causing global temperatures to fall photosynthesis would have halted killing many organisms throughout the food chain large quantities of harmful compounds would have been introduced into the atmosphere which killed many marine organisms along with acid rain that killed vegetation and polluted the water The Chicxulub Impact Crater Result Mass Extinction! 75% of all species became extinct, including the dinosaurs! K-T Impact Survivors What if the Dinosaurs had not become extinct? What would they look like today? 6
Other Mass Extinctions A least 5 major mass extinction events over the past 500 my! A Dinosauroid! The Permian Extinction (245 mya) Not all mass extinctions are caused by impacts! Mass extinctions do not always slow down evolution! By enabling new sets of organisms to dominate, evolution can sometimes be accelerated! Asteroid Compositions Determined by studying reflected light C-type: carbon-rich S-type: rocky M-type: iron-rich 7
Asteroid light curve reveal their irregular shapes! Irregular shapes are evidence for collisions! Asteroid 951 Gaspra Asteroid 253 Mathilde Asteroid 2867 Steins Asteroid 243 Ida Rosetta probe 2008 8
Asteroid 21 Lutetia Most asteroids have densities much lower than solid rock! They are loose collections of rock! Rubble Piles! Rosetta probe 2010 Near Earth Asteroid Rendezvous (NEAR) Mission (2000) Asteroid 433 Eros The Surface of Eros 9
Hayabusa Mission (2005) Land micro rover on surface Collect and return asteroid sample to Earth Arrival at Asteroid 25143 Itokawa Collecting Sample from Surface (11/26/05) September 2005 Not sure whether sample actually collected! June 13 th 2010 Capsule Recovered in the outback of Australia July 2010 Minute particles found in sample container 10
The Dawn Mission Launched September 27 th 2007 Will be placed in orbit about two of the largest asteroids, 1 Ceres and 4 Vesta Will arrive at 4 Vesta in 2011 Will arrive at 1 Ceres in 2015 Uses an ion propulsion system Comets Chunks of ice and dust orbiting the Sun Dirty Snowballs 11
Comets have highly eccentric orbits! Comets are named after their discoverers! Examples: Comet Halley Comet Hale-Bopp Comet Wild 2 The Three Types of Comet Short period: orbital periods < 20 yrs aphelion distances < 7 AU Intermediate period: orbital periods 20-200 yrs aphelion distances: 7-35 AU Long period: orbital periods 10 3-10 4 yrs aphelion distances: out to 1 light year Comet Wild 2 a short period comet Comet Wild 2 Orbital Period = 6.39 yrs 12
Comet Halley an intermediate period comet Comet Halley Orbital period = 76 years Comet Hale-Bopp a long period comet Comet Hale-Bopp Orbital period = 4000 yrs Short and intermediate period comets originate in the Kuiper Belt In 2009 the Hubble Space Telescope discovered a Kuiper Belt Object only 3,200 ft across when it occulted a star The object was 4.2 billion miles away! 13
Long period comets originate in the Oort Cloud A long period comet can be transformed into a short period comet if it passes close to a planet! Sun-grazing comets In 1992 Comet Shoemaker-Levy 9 passed close to Jupiter and was torn into at least 20 fragments! Can sometimes crash into the Sun! In 1994 the fragments crashed into Jupiter s outer atmosphere generating huge fireballs! They left temporary scars in Jupiter s atmosphere which eventually dispersed 14
July 20 th 2009 Infrared (IR) Image 3 rd June 2010 Comets are small typically around 10 km The chunk of ice and dust is called the nucleus of the comet As a comet approaches the Sun, the ices start to evaporate forming a coma When comets are far from the Sun they are very faint and cannot be seen! Most comets are discovered at this stage! 15
A Comet has two tails! When a comet enters the inner solar system it develops a tail which always points away from the Sun! Comet Hale-Bopp (1997) Close-up of a comet at perihelion The Giotto flyby of Comet Halley (1986) The nucleus of Comet Halley Deep Space 1 Mission flyby of Comet Borrely (2001) An icy dirtball! 16
The nucleus of Comet Borrely The Stardust sample return mission Stardust collected samples of dust from Comet Wild 2 in 2004 Samples were successfully returned to Earth in Jan 2006 Deep Impact Mission (2005) Fired a projectile into Comet Temple 1 in 2005 17
Producing a huge explosion on the surface Found that comets have densities much lower than solid ice with a composition similar to a fluffy snowball Comet Hartley 2 The European Rosetta Mission will place a lander on Comet Churyumov-Gerasimenko in 2011 EPOXI probe flyby Nov 2010 Origin of meteoroids? Meteoroids Small rocky debris orbiting the Sun Much more common than asteroids! Asteroid Collisions! 18
A meteor or Shooting Star 300 tons of material fall through the Earth s atmosphere each year! Small rocks completely burn up in the atmosphere Sporadic Meteors Meteors coming from random directions On average we see one sporadic meteor per hour Meteor Shower Many meteors seen coming from a particular direction of the sky at roughly the same time each year A Meteor Shower Radiant = the direction of the sky that the meteors are seen to come from Named after the constellation that the radiant is found in 19
Caused by the Earth passing through the debris left in the orbit of an old comet A Fireball Earth passes through debris at same time each year Larger objects only partially burn up! Fireball over Western Ontario, Canada Result: something hits the Earth! A meteorite! Meteor Crater? Most fall in the oceans or uninhabited areas They are very difficult to identify! 20
A few fall in populated areas! Antarctica the best place to find meteorites! A continent covered with a thick ice sheet Meteors are found lying on top of the ice! There are four main types of meteorites! Carbonaceous Chondrite Meteorite Achondrite Meteorite Fragments of C-type asteroids Fragments of S-type asteroids 21
Iron Meteorite Planetary Achondrite Meteorite Fragments of M-type asteroids Rarest kind! Meteor seen in Martian sky! An iron meteorite found on Mars! 22