Asteroids Titius-Bode Law (1766) 2 The distances between the planets gets bigger as you go out. Johann Daniel Titius ( 1729 1796) Johann Elert Bode (1747-1826) updated May 16, 2013 Titius & Bode came up with a law that predicted the size of the orbits BIG gap between Mars (1.6 AU) & Jupiter (5.2 AU). Predict planet at 2.8 AU Log(AU) 2 1.5 1 0.5 0-0.5-1 y = 0.2387x - 0.6824 R 2 = 0.9945 Mercury Titius-Bode Law Missing Planet Jupiter uranus Saturn Mars Earth 0 1 2 Venus 3 4 5 6 7 8 Ceres Discovered 1801 3 Orbit of 1 Ceres 4 First Asteroid discovered by accident by Piazzi 1801 Giuseppe Piazzi. It s the biggest, 950 km in diameter (small compared to moon) Contains 32% of mass of entire asteroid belt! Combined mass of all asteroids is only 4% of earth s moon Structure of Ceres 5 6 Ceres (Hubble Space Telescope) Mass determined from perturbations on another asteroid [348 May] which make 3 close approaches between 1891 and 1984. Interior is possibly rocky core with icy mantle 60 to 120 km thick (containing about as much as all the fresh water on the earth). Dawn Mission (2007) will arrive at Ceres in Feb 2015 1
The Minor Planets 7 8 Sizes determined from occultations of stars by the asteroid Name 1 Ceres Date 1801 Orbit AU 2.76 Size (km) 950 Notes Biggest Dawn Mission (2007) 2 Pallas 3 Juno 1802 1804 2.77 2.67 500 235 Share orbit with Ceres Stony 4 Vesta 1807 2.36 530 Brightest, Calcium on surface 9 10 Vesta: Recent Data (Dawn Mission) Dawn Mission entered orbit around Vesta on 16 July 2011 for a one-year exploration, and left Vestan orbit on 5 September 2012 Vesta: Recent Data (Dawn Mission) 11 Vesta: Recent Data (Dawn Mission) 12 July 17, 2011 July 24, 2011 Range 5200 km 2
Vesta: Recent data 13 Vesta probably is Differentiated 14 Meteorites with Calcium in them possibly come from Vesta! It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. Debris from this event has fallen to Earth as howardite eucrite diogenite (HED) meteorites, a rich source of information about the asteroid In 1830 more discovered (1 per year) No more found for 38 years 15 90% of asteroids are in the Asteroid Belt between Mars and Jupiter 136,000 cataloged 16 Now several hundred thousand are known between Mars and Jupiter 13,500 have official names. Jupiter s gravity helped shape the asteroid belt 17 Apollo Asteroids 18 Even today, gravitational perturbations by Jupiter deplete certain orbits within the asteroid belt The resulting gaps, called Kirkwood gaps, occur at simple fractions of Jupiter s orbital period First Discovered 1932 Cross Orbit of Earth Icarus goes closer to sun than Mercury! 3
Jupiter s gravity also captures asteroids in two locations, called Lagrangian points, along Jupiter s orbit 19 20 Hilda Asteroids are in a 3/2 resonance with Jupiter Spacecraft have visited a few asteroids. 21 Asteroid Ida has its own little moon, Dactyl, which is 1.5 km in diameter Ida is 56 km long 22 Several small bodies (asteroids, satellites of Mars, and a comet nucleus) shown in their relative sizes Gaspra is 18 km long 23 Mars satellite Phobos 24 Phobos is cratered, but has an overall smooth surface. Note the long grooves and chains of craters. The chains of craters are probably caused by gas coming out of the interior of Phobos. The other craters are from impacts. Phobos is probably an asteroid. 4
Asteroid #216 Kleopatra, mostly made of metal, mapped by reflection of radar signals (2000) 217x94 km. 25 An asteroid mission in progress the Japanese Hayabusa mission at asteroid 25142 Itokawa 26 Itokawa is about 500 meters long it is a Near-Earth asteroid (NEA) A landing device will grab a sample of Itokawa and return it to Earth. This will be the first asteroid sample-return mission. 27 Another Near-Earth asteroid, 433 Eros, was visited by an orbiting spacecraft. The spacecraft was called NEAR (Near Earth Asteroid Rendezvous) 28 Why aren t there any impact craters on this asteroid? (I have no idea!) 29 NEAR took pictures all the way down to the surface. After orbiting 433 Eros for about a year, the spacecraft This frame shows an area about the size of our classroom. settled down onto the surface in a controlled crash landing. 30 Boulders in the bottom of a depression on Eros surface. 5
Asteroids occasionally collide with one another 31 Asteroids collide with one another In these sketches, an asteroid is shattered by a large impact (C). It then reassembles into a broken mass (E), and is again hit by a big impactor (F) and flies apart. 32 A B C Asteroids undergo collisions with each other, causing them to break up into smaller fragments D E F 33 The Zodiacal Light Milky Way 34 Asteroid fragments hit the planets and sometimes fall to the ground as METEORITES Meteorites are free samples of other worlds. Collisions among the asteroids also produce very fine dust particles. These are illuminated by sunlight and form a faint band across the sky, visible at sunrise and sunset. This is the Zodiacal Light Horizon NEA: Near Earth Asteroids The asteroids that have orbits that cross the orbit of the Earth have the possibility to collide with our planet The Apollo and Amor family asteroids are most likely to hit Earth About 2200 Near-Earth (NEA) asteroids are known There are more NEAs that have not yet been found PHA: Potentially Hazardous Asteroids, 836 known, that come closer to Earth than 0.05 AU and about 100m in size, i.e. can cause a global catastrophe. 35 The 1 mile diameter Barringer Crater (Arizona) was probably created by a 45 meter object, 50,000 years ago. 36 6
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