NASA's mission to Mars: what will the 'Mars Observer' space probe teach us about our planetary neighbors?

What will the Mars Observer space probe teach us about our planetary neighbor?

Here it is, the chance of a lifetime. Blast off to Mars--the planet that has stirred human curiosity since astronomers first imagined life could exist there.

You'll be among the first Earthlings to set space boot on its red, iron-rich, dusty soil--soil on which humans may one day build homes. Ten ... nine ... eight ... Ready for takeoff?

Scientists at NASA are planning such a mission, to take place in your lifetime. But before you blast out of your seat to volunteer, there are some things they think you--and they--should know about your destination.

Like what? Well, for starters, what are the surface and atmosphere like? That info will help you decide where to land and what to bring. You might also want to know if you'll freeze to death, and whether you'll be able to breathe. Will you find any resources you can use? And if Earthlings do decide to develop a Mars colony, can we make it feel like home?

IN SEARCH OF ...

NASA scientists started gathering information to answer these questions back in the 1960s and '70s. That's when they launched a series of Mariner and Viking spacecraft to orbit and land on Mars. These probes sent back amazing pictures and other data, which you can see and read about on these pages.

But for every question answered, the scientists came up with new ones to ask. So now they are sending a new wave of space probes to Mars. The first of these second-generation probes, the Mars Observer, was launched September 25, 1992. It should be completing its 11-month journey and positioning itself in Mars orbit as you read this magazine.

The Observer will circle its target for a full Maritian year (that's 687 Earth days to you and me; Mars's orbital pathway around the Sun is much longer than ours). During that time, the Observer will send back detailed Mars maps and readings on conditions such as climate and soil composition. Says project scientist Bevan M. French, the probe "will map parts of Mars better than we have mapped parts of Earth."

What we learn from this other-worldly exploration will teach us much about the history, and possibly the future, of our own planet. Mars, after all, is the most Earthlike of the other planets in our solar system (see comparison table, p. 10).

So you won't want to be caught without your Science World when the data start pouring in. This article will give you some background in the basics--what we know about Mars up to now. Then, later this school year, we'll update you with a special issue featuring findings from the Observer mission and other stories about Mars. Fasten your seatbelts for a fascinating ride!

NOTHING TO DRINK

Much of what we've learned from the Mariner and Viking missions tells us Mars is probably not the kind of place we--or any living thing--would want to call home. For starters, the weather isn't all that "hot." In fact, it's freezing! Lying some 75 million kilometers farther from the Sun than Earth, Mars has an average daily temperature of around -50 [degrees] C (-32 [degrees] F). On some days the temp doesn't climb above -125 [degrees] C. Brrr!

That means you can forget about having a drink of liquid water--a substance required by all the living things we know of. The water that exists on Mars is frozen solid. Some is packed in Earthlike ice caps at the poles. But more probably lies underground --making Mars's surface one solid layer of permanently frozen ground.

Next, consider the problem of breathing: There's virtually no oxygen on Mars. A thin atmosphere encircles the planet, but it's mostly carbon dioxide--the waste gas we humans exhale. No oxygen also means there's no ozone ([O.sub.3]) to screen out the Sun's harmful ultraviolet rays.

So maybe Mars wouldn't be the easiest place to live. But it could still be a pretty awesome place to visit, especially when you consider the places people visit on Earth--canyons, volcanoes, ancient rivers, craters.... Mars, a planet only half the size of Earth, has them all--in some cases, giant versions!

CRATERED MOUNTAINS

Take the volcanoes. While Mars has few of these lava-spewing mountains compared with Earth, the ones it has are enormous. Olympus Mons, the planet's biggest, stretches 600km across and 25km high. It would tower over Earth's largest volcanic mountain, Mauna Kea in Hawaii, which measures only 9km from its base below the ocean to its peak (see diagram, below).

Why such a difference? The answer has to do, in part, with how the two planets' volcanoes were born.

On Earth, volcanoes form when "hot spots" in Earth's molten mantle push up through the crust. Earth's crust, broken up into pieces called tectonic plates, moves around. If a piece of crust that's home to a growing volcano shifts away from the hot spot, the hot spot will push up a new volcano, rather than adding to the size of the first. That's why we see chains of volcanoes in places like Hawaii.

Mars's surface, however, does not appear to have mobile plates, so volcanic forces within that planet continue to act on the same part of the crust continue to act on the same part of the crust over time. The volcanoes grow higher and higher.

Another reason for Mars's great peaks is that they don't have as much gravity pulling them down. As mountains grow on Earth, the added weight (a result of gravity) causes them to slump outward. But Mars, much smaller than Earth, has only one third of our gravity. That means mountains (and everything else) weigh only one third as much, and so, can grow much taller.

RIVERLESS CANYON

Another big attraction on Mars's surface is its 5,000-km canyon, called Valles Marineris. This gash in the planet's surface would stretch across the whole U.S.--that's 14 times longer than our Grand Canyon. Valles Marineris is also more than twice as deep and at least five times wider.

Scientists think Mars's canyon started to form around the same time as its volcanoes, initially as a series of parallel cracks in the crust. Most likely, all that upward pushing against the surface caused the crust to split. Could these have been marsquakes? (The planet is thought to experience some 100 per year, compared with our 6,000 earthquakes.)

Later, scientists think, underground springs of running water carved away at the subsurface material below the cracks--similar to the way the above-ground Colorado River has etched the Grand Canyon on Earth. Eventually, Mars's cracked surface caved in, leaving the deep gorge we see today.

WATERLESS RIVERS

We did tell you there is no liquid water on Mars--just ice. But scientists now say that probably wasn't always the case.

Pictures sent back by Mariner 9 reveal what look like ancient riverbeds. These channels have branching tributaries, just like rivers and streams on Earth. So scientists believe that Mars was once warmer, and that water did flow.

That brings us back again to the possibility of life. Even if life doesn't exist there now, perhaps it once did on a warmer, more hospitable Mars.

The Viking landers took up that question by searching for life's leftovers--organic chemicals in the soil, waste products in the air. They found nothing. But future explorers of Mars will certainly look again.

Of course, there's the chance that they won't be able to identify what they are seeing, says geologist Philip Christensen. He suggests that life on Mars might take a very different form from life on Earth. "There are many scientists who argue that maybe there is life on Mars," he says, but "we just don't know how to look for it yet." Stay tuned.