Here we see a these robotic cousins, the golf-cart-sized MER rover (right)
and a test version of its immediate predecessor Sojourner, no larger than a
microwave.
While both have six wheels, the MER rovers are not mere Sojourner clones in
bigger boxes. Sojourner had to relay its data via a lander, whereas the MER
robot can speak to Earth directly. Both rovers can drive themselves to specific
science targets, but MER's Spirit and Opportunity have collectively driven almost
3 miles (4.8 kilometers) to date, while Sojourner racked up a total distance
of only 328 feet (100 meters) and never ventured farther than 40 feet (12 meters)
from its landing site.
Each MER rover also bears an articulated robot arm laden with spectrometers,
magnets, a microscope imager and a rock abrasion tool. More science instruments
and cameras sit atop a mast, including the famed Pancam
that makes 3-D
images. Using digital technology similar
to a camera you can buy, MER photos are three times sharper than those of
the 1997 Mars Pathfinder mission or the 1970s Viking landers.
Sojourner sent home 550 images. So far, a whopping 39,410 have been returned
by the MER rovers (21,815 from Spirit and 17,605 form Opportunity).
And an entire subset of navigation cameras keep Spirit and Opportunity on their
appointed Martian rounds. The Sojourner rover, on the other hand, carried a
single dedicated science spectrometer, two small black and white cameras, one
color imager and laser for obstacle detection.
