SPACE.com: Who are your heroes in the field of astronomy?

Ken Croswell: My real hero is the universe itself, not those of us who study it.  The universe has created an enormous diversity of planets, stars, and galaxies, yet like snowflakes no two planets are the same, no two stars are the same, and no two galaxies are the same.  And the universe's most amazing creation is life itself, especially us.  Mars may tell us how it started.

Which astronomers and space missions, past or present, do you feel have made the greatest contributions to our understanding of Mars?

Every successful Mars-bound spacecraft has advanced our understanding of the red planet, but the two most important have been the Viking mission, which in 1976 placed two craft into orbit around Mars and two craft on the surface, giving us the first close-up views from the ground below; and Mars Global Surveyor, which went into orbit around the planet in 1997 and has been compared to the Stealth aircraft, since so few people have heard of it.  Yet Mars Global Surveyor has provided sharp images of the surface, mapped Martian topography with unprecedented accuracy (Magnificent Mars presents over a dozen rainbow-colored topographic maps, some of which have never been published before), and discovered hematite--a mineral that forms in hot water--in Meridiani Planum and Aram Choas.  Indeed, the images from this spacecraft strongly hint that water flowed recently, within the past few million years, and so did lava, indicating that the Martian volcanoes are still active today.

How much have modern observations and technology - from the Viking missions and onward - impacted the study of Mars?

A lot.  One reason that Dr. Robert Zubrin--president of the Mars Society--endorsed Magnificent Mars is that he thought the book represented an excellent synthesis of post-Viking results, especially those of the past ten years, when Mars Pathfinder landed, Mars Global Surveyor went into orbit, and Mars Odyssey did the same.  For example, Mars Pathfinder not only gave us the wonderful panorama of the Martian surface, but it also provided colorful views of Martian clouds and Martian sunsets.  Mars Global Surveyor scrutinized sedimentary layers likely laid down by ancient lakes in Valles Marineris, discovered gullies that were likely carved by recent flows of water, and as I mentioned found hematite in Meridiani Planum, convincing NASA to land a spacecraft there this January.  And in 2002 Mars Odyssey detected the subsurface ice that scientists had long suspected at high latitudes, and I was pleased to include the full-color Odyssey ice map as a very large (about 21 inches by 14 inches) spread in Magnificent Mars.

You mention that the Martian surface can yield the planet's 4.6 billion-year history to patient observers. How is that history preserved on Mars, and how is that different from planetary studies here on Earth?

Earth is a great place to live, but the same vigorous activities that sustain terrestrial life--torrential rainfall, enormous oceans, volcanic eruptions, continental drift, and life itself--also obliterate the Earth's past.  As a result, it's very hard to find ancient rocks on Earth:  the oldest known Earth rock is 4.0 billion years old.  It's a lot easier on Mars; in fact, we already have a Martian rock that's 4.5 billion years old, in the form of a Martian meteorite named ALH 84001.  That's because Mars has been a quieter planet over the most recent two thirds of its life and has better preserved its ancient surface.  Consequently, on Mars we can more easily trace the planet's ancient past--a time when life was struggling to arise on the Earth and possibly on Mars.  Indeed, for that reason, Mars may teach us how life got started better than the Earth will.

In the book, you take images from a number of sources, ranging from the Hubble Space Telescope and the Mars Global Surveyor to the Viking spacecraft that made the first red planet landings in the 1970s. What challenges did you face compiling these Mars images in order to tell a comprehensive visual story of the planet?

The goal behind Magnificent Mars was to create the most lavish, most extravagant, most beautiful book ever published about the red planet, using the same format as a previous book of mine, Magnificent Universe.  The biggest challenge was the enormous size of Magnificent Mars itself:  each page measures over 10 inches by 14 inches, and the book itself weighs nearly five pounds.  In order to achieve the best results, I obtained full-color images with the highest resolution, then asked Tony Hallas--an outstanding astrophotographer--to digitally reprocess the images, to try to make each image look even better than NASA's own.  Each image was then printed on thick, semi-satin paper to bring out the very best.  As a result, I hope that Magnificent Mars lives up to its title.

While you were putting together Magnificent Mars, did you come across an image that stuck out from the flock? A personal favorite?

I was afraid you'd ask!  I like 'em all!  I included full-color surface views from all the spacecraft that have successfully landed on Mars--Viking 1, Viking 2, and Mars Pathfinder--and these are neat because they make you feel as though you are standing on the planet's surface.  The rainbow-colored topographic maps of Mars are also outstanding, such as the two-page spread on pages 50-51, which shows the full planet, as well as the labeled topographic maps on the foldout.  Magnificent Mars even includes rainbow-colored topographic maps of Phobos and Deimos, which even most Mars-savvy people have never seen before.  Since the moons of Mars aren't round, they're pretty wild looking.

What is the most important aspect of Mars that you hope readers take away from Magnificent Mars?

That Mars is a WORLD with a life story of its own--a life story that may be easier to piece together than the Earth's.  As I began to plan Magnificent Mars, there was so much to say, but there seemed no good way to organize this material into a coherent story.  Then one day I was looking at the cover of Marillion's album Seasons End, which depicts the four classical elements--Earth, Air, Fire, and Water.  Of course!  Why didn't I think of that?  Almost instantly I realized that this would be the perfect way to unify the story of Mars:  in the Earth chapter, I discuss the core, mantle, and surface of Mars, the planet's birth, and the new results concerning the planet's topography; in the Air chapter, I describe the planet's atmosphere, whose isotopic ratios hint at a warmer and wetter past, and include amazing images from Mars Pathfinder of a Martian sunset and Martian clouds; in the Fire chapter, I show the planet's many--and mighty--volcanoes, the tallest mountains in the solar system, which we now know erupted in recent times, as well as Valles Marineris, the deepest canyons in the solar system, created by the uplift of the volcanic province of Tharsis; and finally in the Water chapter, I present the element that's crucial for life and all the new results concerning Martian ice, floods, rivers, gullies, lakes, and maybe even an ocean.

Most of our views of Mars are from Earth-based telescopes or unmanned spacecraft and robot landers. How important is it to send humans to the red planet and capture the experience with their own eyes?

We need a diverse space program.  We need both unmanned and manned missions.  Unmanned missions are cheap and can go places no sane human should, but we human beings have abilities that no machine will ever match.  For example, I mentioned earlier that Mars has better preserved its ancient surface than the Earth.  If life arose on Mars and left fossils, I would trust a human being to find and recognize them over any machine.

Is Mars the logical next step for the human exploration of space?

I'm not smart enough to know the answer to that.  Mars is much more interesting than the Moon, but the Moon is easier and cheaper to reach.  A Moon base could give us useful experience of living on another world, but it could also create a detour that would detract us from Mars.  My agent, Russ Galen, made an interesting analogy.  He compared this era of Mars exploration to the time of Lewis and Clark.  To most Americans two hundred years ago, Oregon and Washington were far-off, exotic places about which they knew little, if they had heard of them at all.  And today, places like Olympus Mons and Valles Marineris are equally exotic, and few people have heard of them.  Perhaps, a hundred years from now, they will be as familiar as Oregon and Washington.

After all these years, what mysteries does Mars still hold secret?

The greatest mystery is whether Mars ever gave birth to life.  The Earth did, but there's no guarantee that other good planets do the same--the fact is, we don't know how readily life arises, even on a good, warm, wet planet like the Earth.  Billions of years ago, as I show in Magnificent Mars, Mars was wetter and probably warmer.  If Mars independently gave birth to life, then life must arise easily, wherever conditions are right, so trillions of other planets in the universe have also spawned life.  On the other hand, if Mars enjoyed hundreds of millions of years of pleasant conditions but failed to give birth to any life at all, then we Earthlings may be unique.  Either way, the answer is profound.