Spacecraft Study of Asteroids DrBill (20361) Romanishin U. Of Oklahoma and Oklahoma City Astronomy Club

Brief Intro to Asteroids Most orbit in main asteroid belt between Mars and Jupiter Some cross paths with Earth (ALWAYS Wear a helmet when outdoors!) Range in size from pebbles to 1000 km across (about size of Texas) As of yesterday 257,455 asteroids have numbers (good orbits), another 282,913

have lesser known orbits- so, over Half a Million asteroids are cataloged! We think there are ~1.5 million with diameters greater than 1 km (0.6 mile) + “billions and billions” smaller ones *But* all asteroids together have mass only ~0.0005 Mass of Earth ----------------------------------------------------- Rich dynamical structure – interactions with mighty Jupiter

What do asteroids look like? From groundbased telescope, just a dot of light, like a star , but it MOVES We have closeup images of only a handful of asteroids from spacecraft flybys Sometimes, pieces of asteroids hit the Earth- these are asteroids you can hold in your hand

Origin and Composition Asteroids probably remains of a “failed planet” – formation stopped by gravity of forming Jupiter (?) What are they made of? Have good idea from meteorites Similar elements to stuff in Earth

Stony or Metallic 1000s of meteorites in collections around world Bewildering array of detailed compositions But to simplify, meteorites are Stony or Metallic

Stony meteorites have minerals that you would hear about in any intro geology course (olivines, pyroxenes etc) One difference from Earth rocks are the chondrules – BB sized bits of minerals that are OLDEST THINGS WE CAN ACCURATELY DATE Chondrules 4560 Myr old- getting to point we can say “this chondrule 10 Myr older”

Another un-terrestrial feature is existence of metallic (iron/nickel) meteorites Iron a common Earth element, but PURE iron is very rare- most iron oxidized on Earth Iron meteorites show Widmanstatten pattern Effect of Slow Cooling of liquid iron

Pure iron from core of Differentated body Some large asteroids must have formed quickly, melted and differentiated, but then were destroyed by collisions releasing iron meteorites Didn’t quite have time to form one big (planet sized) body before Jupiter formed and disrupted the formation process

First closeup images Prior to 1991, asteroids were dots of light Lightcurves gave some info on overall shapes First asteroid closeup from Galileo, a space probe on its way to Jupiter Galileo- launch 1989 Orbited and studied Juipter and moons from 1995-2003

951 Gaspra from Galileo

(243) Ida and companion Dactyl from Galileo 1993

Galileo images showed: (1) cratering a very important process shaping asteroids (2) binary asteroids did exist

NEAR Shoemaker (Near Earth Asteroid Rendezvous) Launch 1996 Flew by 253 Mathilde in 1997 Entered orbit around 433 Eros on 14 Feb 2000 “Landed” on Eros 12 Feb 2001

movie

Eros regolith

Eugene M. Shoemaker 1928-1997 Meteor Crater Apollo SL9 He got to the Moon.

Hayabusa Japanese effort to land on asteroid and return sample of surface Launch 2003 to 25143 Itokawa “minilander” robot failed Main craft “bump landed” and tried to collect surface particles Capsule returned to Earth – Landed in Australia in June 2010 November 2010 “some particles in capsule definitely from Itokawa”- Stay Tuned

Rosetta One its way to comet 67P/Churimov-Gerasimenko Flew by 2 asteroids: 2867 Steins in 2008 21 Lutetia in 2010

Comets and Asteroids visited by spacecraft Emily Lakdawalla planetarysociety.org

Coming Attractions- Dawn Dawn Extended visits to 2 asteroids Launch 2007 Currently nearing Vesta (Jul 2011- Jul 2012) On to Ceres (Feb 2015- Jul 2015)

3D shapes from Lightcurves