Last week, scientists revealed that parts of Mars, shaken loose by collisions with asteroids, have been colliding with the earth for some time. Many such rocks have landed on the earth and are indistinguishable from earth rocks, the scientists determined. Also last week, at the Institute of Politics, Sen. Alan K. Simpson (R-Wyo.) defended his plan to cut legal immigration. As these two events illustrate, people usually fear the unknown without cause.

For centuries, Mars has inspired fear. The striking redness of the planet portended all sorts of evil to those who viewed it. The Babylonians named it Nergal, after their god of death and pestilence; the Romans called it Mars, after their god of battle. And now we learn that Mars has been among us the entire time. Somehow Mars seems more mundane now.

For at least three centuries, immigration has inspired fear in the United States. The Native Americans resented the British colonists; the English colonists resented the Irish; the Irish resented the Italian immigrants. Now, Simpson is not really speaking against any of these groups since they do not immigrate in significant numbers. They have been among us so long that they no longer inspire fear. But the Asian-American and Latino-American newcomers are still frightening.

Senator Simpson did acknowledge that legal immigration does not hurt the U.S. economy. After all, the Urban Institute has reported that legal immigrants put $25 billion a year more into the country, through taxes, than they take out through services. Simpson stated, however, that legal immigration should be curtailed to appease anti-immigration sentiment across the country. The fear that legal immigrants are using all of the hardworking Americans' money has taken hold of the country, even though the facts state differently.

We should be glad that the world didn't learn of the Martian hailstorm any earlier. Congress might have spent countless dollars building an atmospheric shield. Its members would have had to appease the country when their constituents thought those insidious Martian rocks were soaking up their money by hiding from view all the diamonds in their backyard.

Can we be surprised that people believe legal immigration is the cause of all their problems? After all, this is the same crowd of people that merely 58 years ago believed Martians were invading the earth. When Orson Welles dramatized War of the Worlds over the radio, 20 percent of the six million people listening believed that New Jersey had just been burnt to the ground by Martians. The highways were jammed with people trying to leave; the telephone lines to the police were busy with people asking them to confirm the report.

Of course, all the chaos was blamed on Percival Lowell, who had mapped a system of canals on Mars that he saw through his telescope. Even though he was wealthy, influential and very insistent, a few scientists hesitated to support his views because they couldn't see those canals for themselves. Later it turned out there were no canals; the dots on Mars Lowell squinted at so long probably arranged themselves into lines in his mind. The canals were simply an optical illusion. Lowell was forgiven because he really believed what he saw. But those who supported him without seeing anything were not forgiven.

When a leader such as California Gov. Pete Wilson believes that immigrants cause people to lose jobs and pay large taxes, can we expect anyone to truly question it? If a leader believes strongly in an optical illusion, history will remember him or her as just a misguided fool. But Simpson doesn't even believe that legal immigration is the cause of all the country's problems, because he realizes the facts say otherwise. Yet he does not work to change the country's perception of immigration to fit the facts. Such a leader is cheating the American people. Members of Congress are elected not only to represent their constituents' views, but also to use their own integrity. Simpson is wrong when he says that bills should be passed to appease constituents even when the facts state differently. He has a responsibility to make sure the correct facts are heard.

Even when we know facts in hindsight, it brings a twinge of guilt. How should we feel when we remember, for instance, that astronauts were held in decontamination units to make certain they did not bring any scourges back from space? But bits of Mars have been raining down on us from the beginning of time. Most of what is in the realm of the unknown is no different from what we've known.

We should feel a little ashamed, perhaps, that the entity we've feared for so long is just like us. That rock you skipped across the river last week might have been from Mars or the moon. The stranger you spoke to just yesterday might be a legal immigrant from last year or two centuries ago.

Tanya Dutta's column appears on alternate Mondays.