Asteroids and Meteors Physics 1800 Lecture updated May 17, 2014

2 Titius-Bode Law (1766) The distances between the planets gets bigger as you go out. 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 Johann Daniel Titius ( 1729 – 1796) Johann Elert Bode (1747 - 1826) Missing Planet

Ceres Discovered 1801 at 2.77 AU from sun! 3 Ceres Discovered 1801 at 2.77 AU from sun! First Asteroid discovered by accident by Piazzi 1801 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 Giuseppe Piazzi.

Ceres (Hubble Space Telescope) 4 Ceres (Hubble Space Telescope)

5 Structure of Ceres 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

More “Minor Planets” discovered 6 More “Minor Planets” discovered Sizes determined from occultations of stars by the asteroid Name Date Orbit AU Size (km) Notes 1 Ceres 1801 2.76 950 Biggest 2 Pallas 1802 2.77 500 Share orbit with Ceres 3 Juno 1804 2.67 235 Stony 4 Vesta 1807 2.36 530 Brightest, Calcium on surface

7 Dawn Mission (2007)

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Vesta: Recent Data (Dawn Mission) 9 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) 10 Vesta: Recent Data (Dawn Mission) July 17, 2011

Vesta: Recent Data (Dawn Mission) 11 Vesta: Recent Data (Dawn Mission) July 24, 2011 Range 5200 km

12 Vesta: Recent data 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

13 Vesta probably is Differentiated Meteorites with Calcium in them possibly come from Vesta!

In 1830 more discovered (1 per year) 14 No more found for 38 years In 1830 more discovered (1 per year) Now several hundred thousand are known between Mars and Jupiter

90% of asteroids are in the Asteroid Belt between Mars and Jupiter 15 90% of asteroids are in the Asteroid Belt between Mars and Jupiter 136,000 cataloged 13,500 have official names.

Jupiter’s gravity helped shape the asteroid belt 16 Jupiter’s gravity helped shape the asteroid belt 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

Apollo Asteroids 17 First Discovered 1932 Cross Orbit of Earth Icarus goes closer to sun than Mercury!

18 Jupiter’s gravity also captures asteroids in two locations, called Lagrangian points, along Jupiter’s orbit

Hilda Asteroids are in a 3/2 resonance with Jupiter 19 Hilda Asteroids are in a 3/2 resonance with Jupiter

Spacecraft have visited a few asteroids. Several small bodies 20 Spacecraft have visited a few asteroids. Several small bodies (asteroids, satellites of Mars, and a comet nucleus) shown in their relative sizes

Asteroid Ida has its own little moon, Dactyl, which is 21 Asteroid Ida has its own little moon, Dactyl, which is 1.5 km in diameter Ida is 56 km long

22 Gaspra is 18 km long

Mars’ satellite Phobos 23 Mars’ satellite Phobos 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.

24 Asteroid #216 Kleopatra, mostly made of metal, mapped by reflection of radar signals (2000) 217x94 km.

25 Japanese Hayabusa mission at asteroid 25142 Itokawa, landed Nov 2005, returned samples to earth June 2010 [chondrite type asteroid] Itokawa is about 500 meters long – it is a Near-Earth asteroid (NEA)

26 Another Near-Earth asteroid, 433 Eros, was visited by an orbiting spacecraft in 2001 The spacecraft was called NEAR (Near Earth Asteroid Rendezvous)

27 After orbiting 433 Eros for about a year, the spacecraft settled down onto the surface in a “controlled crash” landing.

28 NEAR took pictures all the way down to the surface. This frame shows an area about the size of our classroom. Boulders in the bottom of a depression on Eros’ surface.

Asteroids occasionally collide with one another 29 Asteroids occasionally collide with one another Asteroids undergo collisions with each other, causing them to break up into smaller fragments

Asteroids collide with one another … 30 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. A B C E D F

Asteroid fragments hit the planets and sometimes fall to the ground as 31 Asteroid fragments hit the planets and sometimes fall to the ground as METEORITES Meteorites are free samples of other worlds.

asteroids also produce very fine dust particles. These 32 The Zodiacal Light Milky Way 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 33 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.

The 1 mile diameter Barringer Crater (Arizona) was probably created by a 45 meter object, 50,000 years ago. 34

Formation of an impact crater 35 Formation of an impact crater Impacts occur at velocities some 10-20 times the speed of a rifle bullet. This produces a powerful explosion. 35

Meteors – Comet dust particles entering our atmosphere and burning 36 Meteors – Comet dust particles entering our atmosphere and burning up from the friction. Every year about Nov. 18 the Earth goes through the path of an old comet.

Meteorites are … Most come from the asteroids, but some are chips from 37 Meteorites are … Most come from the asteroids, but some are chips from the Moon and some are from Mars.

1992 The Peekskill, NY Meteorite Fall 38 1992 The Peekskill, NY Meteorite Fall A meteor streaked across the skies of for 40 minutes, then hit a car

Peekskill Meteorite The car and the meteorite 39 Peekskill Meteorite The car and the meteorite Now in the Smithsonian!

40 A meteorite the size of a car streaks across the sky, headed for Canada, but doesn’t strike the ground. It “skips” off the atmosphere.

October 17, 2012, a car-sized meteor passed northward over the Hayward hills. 41 http://www.youtube.com/watch?v=pFjC04A8_WU http://earthsky.org/space/many-in-bay-area-heard-and-saw-bright-meteor-on-october-17

Feb 15, 2013, Russian Meteor Event 42 Feb 15, 2013, Russian Meteor Event http://en.wikipedia.org/wiki/2013_Russian_meteor_event Videos: http://rt.com/news/meteorite-crash-urals-chelyabinsk-283/ http://www.youtube.com/watch?v=L-VlIWSDbn4

Some meteorites are big 43 Some meteorites are big 15-ton meteorite found in the Willamette Valley, Oregon Known to native Americans, but “discovered” in 1902. Now in the Hayden Planetarium, New York City. 1906 photo This is an iron meteorite

Many meteorites have been recovered in Antarctica 44 Many meteorites have been recovered in Antarctica Meteorites are preserved in the Antarctic ice cap. The are concentrated in certain areas by the motion of the ice. Meteorites are easier to find in the ice because there are very few “native” rocks. A few thousand have been found so far.

Melted and unmelted meteorites come from different kinds of asteroids 45 Melted and unmelted meteorites come from different kinds of asteroids This is an asteroid that has melted and differentiated. The iron has mostly gone to the core. These two asteroids have not melted, and have not differentiated.

Chondrites are meteorites that contain chondrules 46 Chondrite meteorites Chondrites are meteorites that contain chondrules Chondrules are little BB-size blobs of minerals and mineral glass that were once melted and quickly solidified. They look like gravel.

Ordinary chondrites contain metal (iron and 47 Ordinary chondrites contain metal (iron and nickel). Note the tiny shiny flakes in this meteorite.

48 Very important ! The ordinary chondrites have the overall composition (metal + silicate minerals) of the Earth and the other terrestrial planets. If we put the Earth in a giant blender and ground it all up (core, mantle, and crust) into small pieces, it would have the overall composition of an ordinary chondrite. + =

differentiated asteroid 49 This sketch shows a cut through an asteroid that has melted and mostly differentiated. The iron and other metals were sinking to form a core, and the lighter silicate minerals were floating to the top. The asteroid was small, and solidified before differentiation was entirely complete. The outer layer is made of silicate rocks. The core is made of iron + nickel. The intermediate zone is a mix of metal and silicate minerals. We can call this a differentiated asteroid

50 When differentiated asteroids are shattered, they produce at least three kinds of meteorites. Two iron meteorites from the core of an asteroid

A stony-iron meteorite from the region near the core. Note the green 51 When differentiated asteroids are shattered, they produce at least three kinds of meteorites. A stony-iron meteorite from the region near the core. Note the green olivine crystals.

A basaltic meteorite from the volcanic crust of a 52 When differentiated asteroids are shattered, they produce at least three kinds of meteorites. A basaltic meteorite from the volcanic crust of a differentiated asteroid

The Importance of Meteorites 53 The Importance of Meteorites They are the oldest material that we have. Their ages are consistently 4.45 to 4.57 billion years. Meteorite ages are determined from the radioactive atoms in them. You have seen these two figures before …