Post contributed by Henrik Hargitai, NASA Ames and ELTE, Hungary
Everyone has a story. The narrative of who we are is created by us, our actions and interactions, sometimes just drifting with the events we live through. Landscapes like the one shown in Image 1, tell a geologic story. We translate it to human language and categories. Landscapes are the interface between a planetary body, its atmosphere and the cosmic environment. They change, age, and renew. A flood from a distant source, an impact, settling dust, all imprint onto it. Its history is recorded in its materials and its relief. With age, it depicts an ever more complicated story until resurfacing destroys its history. It’s increasingly popular to explain geology by processes. In real life, however, processes are not always clear cut and as we enter the age of multidisciplinary studies, many of us accept people who are different, we also recognize that landforms are shaped by a multitude of processes, they are not black or white, but all shades of… any color. Is a channel volcanic or fluvial? Well, maybe it’s both, and tectonic, too, with a pinch of ice-rich material that is of course sublimating. Even the types of question we can think of evolve, and this is happening in science, humanities and politics in parallel. Lowell’s Mars? Flat plains and marshes. Perhaps he didn’t even have enough creativity? Nature ‘s creativity always surpasses our own.
Still, the combinations of processes acting upon a huge diversity of preexisting terrains result in just a few types of shapes that our brain’s pattern recognition algorithm can easily classify. Looking at an image like those presented here, tell geologic stories that we can read.
When practicing planetary geomorphology, you deal with relief forms, albedo or radar features. Hey, a gully! No, it’s not, don’t you see? It’s just a valley. Training your eyes to recognize and name landform types doesn’t make you a good geomorphologist, though. You’ll also need to know their stories. The way geologists read a landscape – in our case, planetary photointerpretation – is not too different from how art historians read the iconography of a painting or as some pundits read a cover of a magazine. Except that in nature you have only one correct reading while in arts you may (or may not) have many.
In most cases we don’t have that one story: we have multiple possible stories, some are claimed to be more likely, others less, and we may not even have the real one on our menu. We also have the story of its investigation, a truly human story embedded into the fabric of natural science. The morphology-based stories converge into a coherent big picture, a paradigm, some of which we now know were wrong, since most were based on multiple assumptions or speculations made from morphology alone. Results of the latest decades, however, started to change this picture. More and more terrestrial analogs are becoming recognized and studied in the field, and we can associate compositional data with morphology both from orbital and in situ observations. We are now seeing cm-scale details of landforms we previously knew only in km-scale orbital images and we can compare topographic, visual, infrared, multi/hyperspectral, radar, high and low resolution datasets. Still, what a human eye can see is the landscape, a complex set of landforms in a particular geologic and planetary context.
We, hundreds of authors, have identified 600+ distinct landform types on Solar System bodies and created an encyclopedia, where we have summarized what we think we know about these forms. (Here is a visual summary: https://planetcarto.wordpress.com/2015/12/24/planetary-landforms-poster/) We have collected peer-reviewed definitions, morphometric data, formation models, distribution maps and revisited image archives and searched through the latest images to choose the “perfect” type examples. Many of these landform types were found on multiple planets and moons, some only in one place. Discoveries on planetary surfaces seen for the first time (on Titan and the Pluto system) will add more landforms to our encyclopedia next year. With the extreme speed of new discoveries; multiple major and minor conferences and workshops each year with hundreds of presentations; the fight of selling our studies to as many journals as possible; and the need to write full paper-sized proposals, review articles, etc have an increasingly important role not only for students and early career scientists but also for the long time professionals.
But what we really want to hold in our hand, is the Encyclopedia Galactica, which contains all landform types of all planets of the Galaxy. You may want to read, for example, the chapter on the landforms of tidally locked super earths, a review on the relief of the bottom of the subsurface ocean of Europa, the landform list of Hadean Earth, Snowball Earth or the topographic map of Earth in 5 billion years’ time. These, or similar surfaces, could exist out somewhere, right now, so we do have the chance to outline the full evolutionary paths of diverse planetary surfaces, in the foreseeable future.
If we could have an Encyclopedia Galactica in our hands, what would motivate us to work on the next edition of the Encyclopedia of Planetary Landforms? Although no novel discoveries are reported in the book, making and reading this book is a discovery in itself. 600+ review articles make a deep sampling of the complete literature of astrogeology. Creating links between the entries is like tracing back the interactions between forms and processes. Like the Internet itself, this book is finite and infinite at the same time. You can follow the “see also” links and discover the next related landforms – or rather, how we see them today.