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Asteroids Astronomy 311 Professor Lee Carkner Lecture 15 Where is the water on Mars? a) b) c) d) e) Underground In the atmosphere In the polar caps a and b only a and c only What is currently the principle resurfacing agent on Mars? a) b) c) d) e) Water Volcanism Wind and dust Glaciers Impacts Which of the following correctly orders Mars missions from oldest to most recent? a) b) c) d) e) Phoenix, Spirit, Viking, Mariner 4 Viking, Spirit, Phoenix, Mariner 4 Mariner 4, Viking, Spirit, Phoenix Mariner 4, Spirit, Phoenix, Viking Spirit, Mariner 4, Viking, Phoenix What two compounds likely make up the ice caps of Mars? a) b) c) d) e) Water and methane Carbon dioxide and water Carbon dioxide and ammonia Ammonia and methane Water and methane Temperature of Mars Temp of Mars from radiation balance TM = [RS/(2 DS)]½ TS TM = [6.96X108 / (2)(1.5)(1.496X1011)]½ (5778) TM = 227.7 K TF = 1.8TK -460 = (1.8)(227.7)-460 = -50.1 F How good is this estimate? Principle source of error is that we have ignored the effects of Mars’s atmosphere Since atmosphere is very thin, error is small How hot must Sun be for liquid water on Mars? TM = [RS/(2 DS)]½ TS TS = TM /{[RS/(2 DS)]½} TS =(227.7) / {[6.96X108 / (2)(1.5)(1.496X1011)]½} TS= 6926.2 K Quiz #2 Friday Quiz 2 similar format as Quiz 1 ~20 multiple choice/matching ~4 short answer Covers lectures 9-15 bring pencil and calculator Rocks in Space Asteroid -- Meteoroid -- a small piece of rock in space Meteor -- the flash of light when a meteoroid hits the Earth’s atmosphere sometimes called a falling or shooting star Meteorite -- a meteoroid that hits the ground Types of Meteorites Meteorites are classified based on their composition Irons are composed of metal Chondrites are composed of silicates (rock) Irons make up only ~5% of falls But, irons are much easier to find Chondrites look a lot like normal Earth rocks What are the properties of chondrites and irons and how can you identify them? Iron Meteorites Have small depressions on surface caused by heat of passage through atmosphere Often show Widmanstatten patterns when etched with acid Helps to distinguish true meteorites from terrestrial rocks Widmanstatten Patterns Chondrite (Stony) Meteorites Composed of silicates Contain chondrules, small glassy inclusions of material that were heated and quickly cooled Chondrites are old Carbonaceous chondrites also contain volatiles (water and carbon compounds) and thus represent unprocessed material from the very early solar nebula Chondrules The Missing Planet In the 18th century astronomers noticed that there was a gap between Mars and Jupiter with no planets This turned out to be a small planet (diameter 918 km) which he named Ceres This is the asteroid belt The Asteroid Belt Asteroid Myths Are the asteroids debris from a planet that exploded? Is the asteroid belt dangerous to travel through? There is on average about one million kilometers between asteroids Asteroid Facts Size: Ceres (918 km), Pallas (522 km), about 200 larger than 100 km, most are less than 1 km Orbit: Description: very small, irregularly shaped, cratered Formation of the Asteroid Belt Jupiter’s gravity: Ejected most near-by planetesimals Alters the orbits of the remaining asteroids Studying Asteroids Several asteroids have been observed at close range In 2005 the Japanese mission Hayabusa studied asteroid Itokawa and tried to collect a sample for return to Earth Asteroid Features Only Ceres, Pallas and Vesta (the 3 largest asteroids) have enough gravity to form a sphere Asteroids show many craters During the heavy bombardment period asteroid collisions must have been frequent Composition of Asteroids Asteroids are divided into three major groups based on composition S Type C Type M type composed of iron and nickel Formation of Asteroids C type asteroids are found in the outer belt where temperatures are lower Need low temperatures to keep volatiles Formation of Meteoroids Some asteroids became large enough to differentiate decay of radioactive materials provided the heat These asteroids were then broken up by collisions Fragments of the crust form achondritic stonys Asteroids that never differentiated formed chondrites NEOs Some asteroids cross the Earth’s orbit and are called Near Earth Objects (NEO) About 1 big one every few hundred years Consequences of impacts Local damage and small climate change Very large tidal waves Mass extinctions What Use is an Asteroid? Mining Space Habitats Spaceships Put engines on the space colony Providing Material for Life in Space Summary Asteroids are small bodies that orbit the Sun Most are in the asteroid belt between Mars and Jupiter (2-3.5 AU) Jupiter’s gravity prevented the asteroids from forming a planet Description: Small (most less than 1 km) Max size is few hundred km Irregularly shaped Heavily cratered Summary: Meteoroids Iron made of metal formed from core of asteroids (M type) Achondrites (Stony) made of rock with no inclusions made from crust of asteroids (S type) Chondrites (Stony) made of rock with small inclusions made from undifferentiated asteroids (S and C type)