Lee James, age 12, of Houston, Texas, for the question:
How big is Mars in relation to the earth?
We expect that Mars will be the first planet our astronauts will visit when mankind sets forth to cross the vast ocean of space. Naturally then, we are all curious about what this new world will be like, Many of the answers will have to wait until we get there. For example, we do not know for sure whether there is any kind of plant life on the Red Planet, though most experts suspect that there are at least plants. We do, however, know a great deal about the planet itself and have a good idea what precautions and protections the first visitors to Mars will need.
Most of us know that Mars is somewhat smaller than the earth, but we tend to think that this is not important enough to make much difference. This is far from true. Mars is a good deal smaller than the earth and this will make a great deal of difference to our earth¬trained muscles. One good way to measure a planet is from its diameter, a straight line from side to side through the exact center. The diameter of the earth is about 7,927 miles. The diameter of Mars is about 4,200 miles.
In this respect, Mars is only a little more than half as big as the earth, In volume, the earth could swallow almost seven planets the size of Mars. Wha t t s more, the earth i s made of much denser material and therefore heavier for its size.
If placed on the earth's surface, the weight of Mars, because of both its Smaller size and lesser density, would be equal to only .11 the weight of the earth. On the scales, it would take slightly more than nine Mars sized planets to equal the earth.
The surface gravity of a planet depends upon its size and weight. Since Mars is both smaller and made of lighter materials than the earth, we would expect it to have less surface gravity. And this is so. Old Andy, who weighs one hundred pounds on this beautiful planet, would weigh only 38 pounds on the planet Mars.
The visiting astronauts will have quite a time adjusting to the light Martian gravity. The energy used to take a three foot stride on earth will be enough to take a seventy foot stride on the Red Planet: If you can jump three feet into the air on earth, on Mars you could jump eight feet above the ground. Earth trained muscles will have to get used to this easy way of doing things.
This light gravity may be a nuisance to earth trained bodies, but it will be a great help to earthman's dreams. For countless ages, man has dreamed of visiting other worlds across the vast oceans of space. So far, the mighty gravity of the earth has stopped his escape. It will be far easier to escape from the lighter gravity of Mars. Who knows, the little Red Planet may one day have a spaceport from which great ships take off to find new Solar Systems around distant stars.