Walt Kelly had it right. Two inhabitants of his Pogo comic strip stand in the Okefenokee Swamp gazing up at the stars. One asks the other whether he thinks there might be life on other planets, maybe life more advanced than us. On the other hand, he speculates, maybe we are the most advanced creatures in the whole universe.
“Either way, it’s a mighty soberin’ thought,” comes the reply.
Millions of people have been caught up in humanity’s latest attempt to explore Mars, perhaps because of the sheer daring and cleverness of the mission design. Who would have thought that you could combine the use of a parachute, small rockets, and giant airbags–airbags?–to land safely among all those rocks on Mars? Or make a pyramid-shaped design where every side is the same, so that no matter which side faced up after Pathfinder stopped bouncing and rolling, it could open up and let the Rover come out?
Or even, by putting these ideas together, and reusing existing designs, you could go to Mars for less than a tenth of the cost of the first Mars landing 20 years ago?
The rover may look like a radio-controlled toy truck but it has its own little laser feelers and computer brain to help it avoid obstacles. These sensors are critical because it takes 10 minutes for radio signals to travel the 100 million miles from Earth to Mars and 10 more minutes to return.
That means if the rover came to the edge of a cliff and sent back a picture from its TV eye, and you radioed, “Stop!” it would be wheels-up at the bottom of the precipice before it heard your warning.
If you drive a model of the rover (you can do so at the Adler Planetarium) you’ll immediately be struck by the challenge of controlling something by remote TV–even without the radio delay. With a 20-minute delay, you might find navigating impossible. Yet it’s being done. And as the rover holds the University of Chicago’s X-ray spectrometer up against the rocks, to sense what they’re made of, we see it not only working but working well.
But perhaps the biggest reason for the fascination is not the technical wonders, but the thoughts that the exploration of Mars inspires about Earth and ourselves. In the same way that travel to a foreign country can give us a new self-image and perhaps a new appreciation of home, the Mars visit casts our home planet in a new light.
“It looks just like Arizona,” or “west Texas,” or “eastern Washington,” I’ve heard people say about the images streaming back from the Pathfinder spacecraft and Sojourner rover. Some enterprising computer artist could take an image of a cactus, and paste it right in, thereby instantly starting a cult.
But appearances are deceiving. Mars differs from Earth in critical ways. For one, it’s a lot colder. Daytime summer temperatures (as at the site where Pathfinder landed) reach only 10 degrees Fahrenheit, and at night fall to more than 100 degrees below zero. The air is thin, much thinner even than at the top of Mt. Everest, and it has little oxygen. Winds can roar more than 100 of miles an hour, engendering planet-wide dust storms.
And the surface of Mars is very dry. Although the planet’s polar caps can be seen even in backyard telescopes, they are a mix of ice and dry ice–frozen carbon dioxide.
Mars is a grand world of magnificent scale, though. It is home to the largest volcano we know of in the solar system. Olympia Mons dwarfs not only Mauna Kea, but the entire island of Hawaii
So lengthy is Mars’ biggest canyon, the Valles Marinaris, that it would stretch from San Francisco to Washington, D.C.
Some of the excitement of Pathfinder’s exploration is occurring because a strategy designed to allow us to sample the rocks from more than one place with a single landing seems to be working out. The landing area was chosen to be in a region where photographs taken from space on previous missions suggested that water had flowed in the past.
By landing in a floodplain, one could hope to see rocks washed “downstream” from different places. Such evidence that large amounts of water were once present on the surface of Mars was a very laudable goal in itself. Indeed, initial photographs show jumbles of rocks that look as expected after a flood. The first rock examined, dubbed “Barnacle Bill,” is volcanic, likely to have been transported to its current site from elsewhere. That rock looks a lot like it could have come from a volcanic site in the Andes.
That and other evidence lead to an interesting speculation: Maybe Mars is not such a “dead” planet geologically as previously thought.
By dead, scientists mean that Mars stands in contrast to the Earth which is geologically alive because it still is hot inside. Molten rock can well up and power active volcanoes.
But Mars is a smaller planet, so it would cool faster. Just as one slice of pizza cools off more quickly than a whole pizza (this is a rare edible experiment that you may try for yourself). Larger objects take longer to heat or cool, so it has been thought that Mars cooled off a long time ago. But if that cooling happened more recently, Mars may have been more Earthlike than previously thought.
A misfortune (from a human point of view) inherent to a small planet such as Mars is that the gravitational pull on its surface is less than on Earth. While this is nice if you’re a high jumper, allowing leaps approaching 20 feet, or if you want to lose weight–a 200-pound human weighs only 76 pounds on Mars–it also means that your atmosphere is gradually escaping.
Mars’ atmosphere is thin today because gravity cannot hold it, allowing it to slowly leak away into space. Loss of an atmosphere brings another misfortune, so far as humans are concerned: loss of the “greenhouse” effect.
Most of us are used to thinking of that as a bad thing. The effect happens when energy comes in, but can’t easily get out, heating an object. It happens in your parked car. Visible light from the sun shines through the windshield, and heats the car inside. The heated seats radiate infrared light (which you can’t see but can feel as heat), but glass is not transparent to infrared light, so it can’t get out and the inside of your car heats up.
The same thing happens to a planet–its atmosphere can trap heat just like a car’s winshield. If we were to pollute the Earth’s atmosphere and increase the greenhouse effect, we could make the Earth too hot and suffer disastrous consequences.
But think of Mars.
Today it is very cold. In the past, with a thicker atmosphere and more volcanic gases, the greenhouse effect would have made it warmer. A warmer, wetter Mars with a thicker atmosphere would have been more conducive to life as we know it.
But we must be careful not to get carried away before we have sufficient data. We have a tendency to do that, especially where Mars is concerned. In the past, lack of knowledge allowed us to people Mars with creatures of our imagination.
Percival Lowell, a great exponent of life on Mars, said in 1895: “One deduction from this thin air we must be careful not to make (is) that it is incapable of supporting life . . . Lungs are not wedded to logic, as public speeches show, and there is nothing in the world to prevent . . . a being with gills, for example, from being a most superior person.”
But, as the great physicist Richard Feynman put it, “Science is a way of trying not to fool yourself.”
By that he meant that no matter how clever or logical an idea, we shouldn’t completely believe it until we have data–actual evidence–in hand.
Is the universe teeming with life? Or are we completely unique? What’s your pleasure?
The scientific approach is to go out and take a look.
The wonder with us today is that after hundreds of years of speculating about what other worlds such as Mars might be like, we stand on the threshold of holding the evidence in our robotic, and perhaps later human, hands.
