by Shane L. Larson
I had the good fortune of knowing all my grandparents. My maternal grandfather, Robert Steele Kelher, Sr., was a chemist. I have vivid memories of spending time with him when I was young, but I don’t recall much of what we talked about. Now that I’m all grown up and a physicist, I often wish I could chat science with him. But one conversation I do remember vividly, was about Ford Thunderbirds. My grandfather once told me he had always dreamed of owning a Thunderbird. But in those later days of his life, when we would walk around the backyard together just chatting, he said he was glad he never got one; he was sure it would never have been as great as he imagined. He preferred the simple joy of savoring the idea of owning a Thunderbird.
I stumble across this memory now and then, and think about my own longings. This week, I am reminded that I often dream of Mars. I imagine an alternate reality where I get up in the morning and don a spacesuit instead of Levi’s, and walk the cold red deserts looking for clues to where we came from, clues to how Mars has changed over the aeons, and clues to what its future fate may be. But interspersed with those idle scientific longings and ponderings of an “other career” are daydreams about living and playing on Mars. What I wouldn’t give to spend a week, camping on Mars near the abandoned hulk of Spirit, once our faithful emissary on the Red Planet. Spirit was one of two Mars Exploration Rovers that landed on Mars in 2004, the ’57 Thunderbirds of their time. It spent a more than 2000 days roving across Mars, covering a total of 7.7 kilometers. Sprit has a twin, called Opportunity that is still roving, and this week we celebrated its 12th birthday on Mars.
I’m not yet as old as my grandfather was when we talked about Thunderbirds, but as I get older, I’m beginning to think that my future will forever be confined to the surface of the Earth. My wonderful daughter fears that she is preventing me from becoming an astronaut (an idea she is firmly against, especially after seeing “The Martian”). She has repeatedly seen us throw space probes and rovers at Mars, but she doesn’t have the perspective to know that while sending humans into space is possible, it is not easy.
Despite my fear that I was born a bit too early to be part of the generations that live and work in space, I feel fortunate that I have lived through the first age of Mars exploration. I’ve been witness to the years when our species obtained its first up close views of the red sands of Mars, and found the landscapes to be not as alien as we might have expected. Pick up any picture, any panorama from Mars and take a good look. Looking across the rubble strewn plains, across the shifting dunes of sand toward soaring mountains rising in the distance, you could easily believe you are looking at a picture of the American Southwest.But this is not Earth. This world is Mars. It does look like Earth, in many ways, and that is part of the reason it captures our imagination. Like people, every world is unique — they have their own individual characters, their own long histories, their own destinies to fulfill in the Cosmos. But also like people, they are similar as well — the laws of Nature that govern the Earth govern Mars. We can take what we know about Earth, and what we don’t know, and use it to learn about Mars. Mars has its own remarkable moons, atmosphere, climate, and orbit; it has a long history of physical processes that shaped the evolution of its surface. Understanding the similarities and differences between Mars and Earth is one part of the long quest to understand our own planetary home. Understanding the similarities and differences is one of the principle reasons we send our robotic emissaries to other worlds. Why does Mars fascinate us so? More than any other world (except perhaps the Moon), Mars has captured the imagination of humans. It is the only planet whose surface can be studied telescopically, and even from Earth there are tantalizing views of a dynamic and changing world. The polar ice caps grow and receed with the seasons, visible even in a small backyard telescope. The vast dark plain of Syrtis Major darkens and fades with the Martian seasons. The planet clearly rotates when viewed from afar, and every so often, globe girdling dust storms blanket the planet, a doleful display that other worlds have dramatic weather patterns of their own. We can see much, and what we can see itches our curiosity and engenders questions.
The Martian atmosphere is thin (only about 1% as thick as Earth’s), but it is still strong enough to toss dust around the planet in globe-girdling dust storms that envelop the world for months on end. Our spacecraft have watched (and encountered!) swirling dust devils meandering across the plains, and rimes of frost condense out of the cold winter air. Once, long ago, we think the atmosphere was thicker, thick enough to move liquid water around the planet in a vast hydrological cycle like ours on Earth. What happened to Mars’ atmosphere? Why and how did it change, and what does that mean about our long term future? The Martian poles are studded by brilliant white ice caps that grow and shrink with the Martian seasons. As the poles grow and shrink, does the ice entomb a layered record of Mars’ storied past, like the Earth’s ice does?
One side of Mars is bulged out in a geologic area known as the Tharsis Bulge. It is a vast volcanic plateau dominated by four massive shield volcanoes, the largest of which is three times higher than Mount Everest as as wide as the state of Washington — it is the largest mountain in the solar system. We call it Olympus Mons. How did this massive volcanic landscape form? Why is it higher than the rest of Mars? Was it created in some astronomical cataclysmic event, or is there something about Mars’ geologic past that made it prone to massive mountain building?
Since the 1960’s we’ve been sending spacecraft to Mars, and they’ve been dutifully sending back pictures and discoveries that lead to more questions. Mars, more than any other world, is the objet du désir. So as the Space Age unfolded, it was the target of many “firsts.”
Mars was the first planet to ever be visited by interplanetary spacecraft. On 15 July 1965, Mariner 4 flew past Mars, returning the first up close pictures of that distant shore. The very first picture was returned to Earth, but with some anomalous housekeeping data that suggested something might be wrong with the spacecraft’s tape recorder. While the issues were being sorted out and the computer was processing the data, the flight team had enough time to hand draw the first image directly from the data, pixel-by-pixel in true paint-by-number style. The first picture we saw was hand drawn (the computer later caught up and confirmed it could draw just as well as the Mariner 4 flight team). In all, Mariner 4 returned only 22 pictures, but those pictures showed us a barren, rocky world pock marked by craters, not (we thought) unlike the Moon.In November 1971, the Mariner 9 spacecraft successfully inserted itself into Martian orbit, becoming the first spacecraft to orbit another planet. Orbiting mars for 349 days, it returned more than 7000 pictures. Hidden among that treasure trove of images were amazing discoveries, including enormous volcanoes larger than any we have ever seen on Earth, and a vast chasm that girdled the planet, now called Valles Marineris — the Valley of the Mariner Spacecraft. Mars was the first planet to ever be landed on. On 20 July 1976, Viking 1 settled down in a rock-strewn red desert called Chryse Planitia — Greek for the “Plains of Gold.” Viking 2 landed just 45 days later, 6475 kilometers away in an equally stunning Martian plain called Utopia Planitia. Together, the Viking landers worked on the surface for 3621 days, returning images, monitoring the atmosphere, and sifting the sands of Mars for indications of life. Mars is, to date, the only planet ever visited by rovers. The first was Sojourner, a micro-rover the size of a toaster oven that travelled a grand total of 100 meters in 1997. It was followed in 2004 by two larger Mars Exploration Rovers called Spirit and Opportunity. Today we celebrate Opportunity‘s 12th birthday on Mars; Spirit roved for six years before it fell silent in 2010. And in 2012, and even larger rover named Curiosity was lowered to the red sands of Mars using an ambitious and daring landing technology called a sky crane. All told, the rovers have covered nearly 60 kilometers among them, and the total is still climbing as Opportunity and Curiosity continue to roll.
All these “firsts” are fun and amazing to be sure. They inspire a kind of astonishment and awe that goes hand in hand with the uncontrollable urge to blurt out, “I can’t believe they just did that!” But in the end, the things that speak to me the most about Mars, the tantalizing bits that draw the mind and the soul into pondering the shifting red sands, are the pictures. The pictures inspire an unrequited longing to walk where none have walked before.
As I myself have grown older, I’ve learned to appreciate my grandfather’s thinking about his dream Thunderbird, especially in a society that seems increasingly commercialized. But when I think about Mars, when I imagine even just a few moments of being able to shuffle around in the light gravity, to turn over a stone scoured by a billion years of Martian weather, to let the red, red sands sift through my outstretched fingers, the longing for that experience is almost overwhelming. Given the chance, I think I’d trade the daydream for the opportunity. But Grandpa? You should know I remembered what you said, and I thought hard about it first.