Asteroids

Asteroid Belt Between Mars and Jupiter there are a number of objects. All are much smaller than a planet. The small amount of light led them to be named asteroids. Mars’ orbit Main belt Jupiter’s orbit

Minor Planets Ceres is the largest asteroid (933 km diameter). 26 asteroids have diameters greater than 200 km. These major asteroids show some differentiation into layers like a planet, including lava flows.

Jupiter’s Pull Jupiter’s gravity keeps asteroids from growing too large. Its gravity also keeps bands of asteroids together with gaps like planetary rings.

Types of Asteroids C-type 75% of asteroids extremely dark (albedo 0.03) oldest material, carbon and other minerals. S-type 17% of asteroids bright (albedo 0.10 to 0.22) iron mixed with silicate rock. M-type 8% of asteroids bright (albedo 0.10 to 0.18) pure iron with nickel and other metals.

Mathilde Mathilde is a main-belt asteroid (66 km long). It is a dark type C. Impacts in Mathilde result in little splash at craters. NEAR/Mathilde

Trojan Asteroids The law of gravity permits an orbit around the sun exactly 60º ahead of and behind Jupiter, called Lagrange points. Several hundred Trojan asteroids are known. There are small asteroids locked to other planets. L4 Trojans Jupiter L5 Trojans

Near Earth Asteroids Asteroids nudged by Jupiter’s gravity head into the inner solar system. Many of these now have orbits that cross the orbit of Earth.

Eros Eros is another near-earth asteroid (30 km long). It is a bright type S. Impacts create boulders that rest on its surface. The NEAR spacecraft also visited here, and safely touched down on the surface. NEAR/Eros next