The Solar System

PART 4 | THE SOLAR SYSTEM

Most asteroids are too small for their

gravity to pull them into a spherical

shape. Impacts break them into

irregularly shaped fragments.

Visual-wavelength image

Enhanced visual image

Visual

Eros appears to be a

solid fragment of rock.

The surface of

Mathilde is very

dark rock.

5 meters

50 km

5 km

If you walked across the

surface of an irregularly

shaped asteroid such as

Eros, you would find

gravity very weak; and in

many places, it would

not be perpendicular

to the surface.

Like most asteroids,

Gaspra would look

gray to your eyes;

but, in this enhanced

image at left, color

differences probably

indicate difference in

mineralogy.

10 km

Visual-wavelength image

1

1a

Seen from Earth, asteroids look like faint points of light moving in front of distant

stars. Not many years ago they were known mostly for drifting slowly through the field of

view and spoiling long time exposures. Some astronomers referred to them as “the vermin of

the sky.” Spacecraft have now visited asteroids, and the images radioed back to Earth show

that the asteroids are mostly small, gray, irregular worlds heavily cratered by impacts.

The Near Earth Asteroid Rendezvous (NEAR) spacecraft

visited the asteroid Eros in 2000 and found it to be heavily

cratered by collisions and covered by a layer of crushed

rock ranging from dust to large boulders. The NEAR

spacecraft eventually landed on Eros.

The mass of an asteroid can be found from its

gravitational influence on passing spacecraft.

Its volume can be measured using images

made from a range of perspectives. The

density is mass divided by volume. Mathilde,

at left, has such a low density that it

cannot be solid rock. Like many

asteroids, Mathilde may be a rubble

pile of broken fragments with large

empty spaces between fragments.

NASA

NASA

NASA

NASA