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Asteroids Astronomy 311 Professor Lee Carkner Lecture 15 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 =(273) / {[6.96X108 / (2)(1.5)(1.496X1011)]½} TS= 6926.2 K Rocks in Space Asteroid -- Meteoroid -- a small piece of rock in space Meteor -caused by friction Meteorite -- a meteoroid that hits the ground Types of Meteorites Two major types are iron and chondrite Chondrites are composed of silicates (rock) Chondrites are the most common type of meteorite 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 Composed of iron and nickel Called regmaglypts These are a particular type of crystal that forms only by very slow cooling (millions of years) Helps to distinguish true meteorites from terrestrial rocks Widmanstatten Patterns Chondrite (Stony) Meteorites One distinguishing feature is a fusion crust where the outer layers are heated by friction with the atmosphere Origin uncertain, but indicate that chondrites have never been strongly heated 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 1801 G. Piazzi found a faint moving star in the gap Ceres was too small to be the missing planet, but soon many more smaller objects were found 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 (544 km), Vesta (529 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 Scheduled to move to Ceres in 2015 Asteroid Types S Type M type C Type composed of carbonaceous chondrite material C type asteroids tend to be found in the outer asteroid belt where temperatures are lower Formation of Meteoroids heavier materials (like iron) sank to the core, while lighter elements (silicates) formed the crust decay of radioactive materials provided the heat Fragments of the core form iron meteoroids Asteroids that never differentiated formed chondrites NEOs NEO’s can hit the Earth About 1 big one every few hundred years Consequences of impacts ~50 m diameter ~100 m diameter costal hit Mass extinctions ~1 km diameter 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)