For many years, the United States space agency has studied the major planets in
An artist''s picture of the Dawn
spacecraft
detail. For example, NASA
is observing Mars from orbit and also on its surface with the Mars Rovers.
Jupiter has also been visited several times by Pioneer, Voyager and Galileo
spacecraft. The Deep Impact mission even visited a comet. But there are
objects in our solar system that remain mysterious. These are the asteroids and
dwarf planets. Now NASA has designed a mission that will visit two of
the important members of this group of objects. A new spacecraft called Dawn
will visit Ceres and Vesta, two large bodies in what is known as the
asteroid belt. The asteroid belt took shape early in the formation of the solar
system, about four and one-half billion years ago. Astronomers believe that the
force of gravity from Jupiter prevented the rocky material between it and Mars
from forming a planet. The result is that there are thousands of rocky bodies
circling the sun between the orbits of Mars and Jupiter.