Related ASU Research Stories
Making Tracks on Mars (feature)
Related ASU Web Sites
ASU Mars Education Program
Related Internet Sites
Jet Propulsion Laboratory
Publication Date: Spring 2005
The robotic wheeled rovers Spirit and Opportunity are landmarks in the modern exploration of Mars. Looking for clues contained in the minerals of the actual Martian surface is a new technique. The method has revealed unprecedented scientific evidence for water in the Red Planet’s past. However, the search for water on Mars is not new.
In fact, scientists have been talking about the possibility of water and life on Mars for hundreds of years—but with some big differences.
The Mars that the MER rovers explore is one that is known to be incredibly dry and cold. The scientists controlling the rovers are looking for evidence of how life might have once existed in the very distant past, or how life might somehow, as incredible as it would be, still exist there today.
Scientists of the past were far less cautious in their assessments. Many took life on the Red Planet for granted. The famous Dutch astronomer Christiaan Huygens observed Mars during the 17th century. He calculated Mars to have a day about the same length as an Earth day. He believed that Mars might support life, maybe even intelligent life, and wrote a book on the subject in 1698.
Also in the 17th century, the Italian astronomer Giovanni Domenico Cassini was the first to notice telescopically that Mars had a polar cap.
In the 19th century, astronomer Frederick William Herschel spent more than 15 years observing Mars. Herschel noted the seasonal changes in the polar caps and speculated that they were composed of ice and snow.
Herschel also came to believe that Mars had “a considerable but modest atmosphere.” Herschel even wrote of Martian inhabitants, and said they “probably enjoy a situation similar to our own.”
For some 19th century astronomers, water on Mars was more than a possibility. It was certainty. During the 1870s, the Italian astronomer Schiaparelli saw a Mars where the polar caps froze during winter and melted in the summer. The water from the melting poles produced temporary oceans. He also saw a complex system of channels that provided much needed water to the organic life that he thought existed along their banks.
Later during the 1890s, the American astronomer William Pickering claimed to have seen 40 large Martian lakes and clouds about 20 miles above the Martian surface. Pickering would later team up with the wealthy Bostonian Percival Lowell, who founded the Lowell observatory in Flagstaff, Arizona. Their initial collaboration was to study the hydrographic features of Mars.
Pickering decided that the reason the channels were visible from Earth through a telescope was not that they were incredibly wide, but because there was plant life growing along their edges when the water was flowing. He thought the vegetation explained not only the visibility of the channels, but also the areas of Mars that seemed to darken on a seasonal basis.
Lowell claimed that this vegetation was the agricultural system of an intelligent Martian civilization. Other scientists were more cautious, but believed that life was very probable on Mars.
In 1909, the observations of the Greek-born astronomer E.M. Antoniadi would put a conclusive end to the idea of channels and agriculture on Mars. But life and water on Mars remained a near certainty—even in Antoniadi’s mind.
That idea remained the accepted idea when Mariner 4, NASA’s first flyby mission of Mars, sent back its first images. It was 1965. But scientists still expected to see some kind of plant life on the planet’s surface. Many speculated that lichens or some other primitive form of plant life might survive on Mars’ frigid surface. But the pictures sent back by Mariner 4 looked remarkably barren. The surface looked a lot like the Moon. Mars had spoken with a colder, drier voice than scientists had expected.
Further exploration with other orbiting spacecraft made it clear—any warm watery period on Mars would have to be buried deep in its past.—Matthew ShindellPhysical Science: Space Science