Mars

DATA BANK

Mars.

Picture Death Valley at its worst. Barren desert. Nothing but rock and sand. Remove every trace of life: get rid of each and every cactus, every bit of scrub, all the lizards and insects and sun-bleached bones and anything else that even looks as if it might have once been alive.

Now freeze-dry the whole landscape. Plunge it down to a temperature of a hundred below zero. And suck away the air until there’s not even as much as you would find on Earth a hundred thousand feet above the ground.

That is roughly what Mars is like.

Fourth planet out from the sun, Mars never gets closer to the Earth than thirty-five million miles. It is a small world, roughly half the diameter of ours, with a surface gravity just a bit more than a third of Earth’s. A hundred pounds on Earth weighs only thirty-eight pounds on Mars.

Mars is known as the red planet because its surface is mainly a bone-dry desert of sandy iron oxides: rusty iron dust.

Yet there is water on Mars. The planet has bright polar caps, composed at least partially of frozen water-covered over most of the year by frozen carbon dioxide, dry ice.

For Mars is a cold world. It orbits roughly one and a half times farther from the sun than the Earth does. Its atmosphere is far too thin to retain solar heat. On a clear midsummer day along the Martian equator the afternoon high temperature might climb to seventy degrees Fahrenheit; that same night, however, it will plunge to a hundred below zero or lower.

The atmosphere of Mars is too thin to breathe, even if it were pure oxygen. Which it is not. More than ninety-five percent of the Martian “air” is carbon dioxide; nearly three percent nitrogen. There is a tiny amount of oxygen and even less water vapor. The rest of the atmosphere consists of inert gases such as argon, neon and such, a whiff of carbon monoxide, and a trace of ozone.

Still, Mars is the most Earthlike of any other world in the solar system. There are seasons on Mars—spring, summer, autumn, and winter. Because its orbit is farther from the sun, the Martian year is nearly twice as long as Earth’s (a few minutes short of 689 Earth days) and its seasons are correspondingly much longer than Earth’s.

Mars rotates about its axis in almost the same time that Earth does. A day on Earth is 23 hours, 56 minutes, and 4.09 seconds long. A day on Mars is only slightly longer: 24 hours, 37 minutes, and 22.7 seconds.

To avoid confusion, space explorers refer to the Martian day as a “sol.” In one Martian year there are 669 sols, plus an untidy fourteen hours, forty-six minutes, and twelve seconds.

Is there life on Mars?

That question has haunted the human psyche for centuries. It is the primary force behind our drive to reach the red planet. We want to see for ourselves if life can exist there.

Or once did.

Or does now.