We live in an infinite itineration of current moments. All we have left are memories, choices, and many paths we do not take. We also have stories and in my case the wish to explore the realm of what could have been. Poems about connection, resignification, love and ultimately decisions. To wonder how we are all connected not only to others, but also to other versions of oneself, with an ink trace that binds everything together and brings it into this wonderful present.

The planet Venus is the closest neighbour to the Earth and in several respects similar to our globe. It revolves around the Sun at an average distance of 0. 72 astronomical units, in an elliptical orbit of eccentricity 0. 007. The corresponding 3 numbers for the Earth are 1 and 0. 017. The mean density of Venus is 5. 2 g/cm , 3 that of the Earth 5. 5 g/cm . Venus’ acceleration of gravity at its equator is 8. 9 2 2 m/s , compared with 9. 8 m/s at the Earth. The escape velocity is 10. 4 km/s, while the corresponding ?gure of the Earth is 11. 2 km/s. Although the mass of Venus is somewhat smaller than that of the Earth – the ratio is M /M =0. 815 V E – the diameters of the two planets are almost the same. In other words, Venus is indeed a sister planet of the Earth. In earlier times, when almost nothing was known about the physical con- tions of Venus, the similarity appeared even stronger than today. Not only was Venus’ period of rotation thought to be close to that of the Earth, it was also p- sible (and indeed common) to imagine intelligent life on Venus.

From September 2007 to June 2008 the Space Studies Board conducted an international public seminar series, with each monthly talk highlighting a different topic in space and Earth science. The principal lectures from the series are compiled in Forging the Future of Space Science. The topics of these events covered the full spectrum of space and Earth science research, from global climate change, to the cosmic origins of life, to the exploration of the Moon and Mars, to the scientific research required to support human spaceflight. The prevailing messages throughout the seminar series as demonstrated by the lectures in this book are how much we have accomplished over the past 50 years, how profound are our discoveries, how much contributions from the space program affect our daily lives, and yet how much remains to be done. The age of discovery in space and Earth science is just beginning. Opportunities abound that will forever alter our destiny.

From the #1 New York Times bestselling author of Anathem, Reamde, and Cryptonomicon comes an exciting and thought-provoking science fiction epic—a grand story of annihilation and survival spanning five thousand years. What would happen if the world were ending? A catastrophic event renders the earth a ticking time bomb. In a feverish race against the inevitable, nations around the globe band together to devise an ambitious plan to ensure the survival of humanity far beyond our atmosphere, in outer space. But the complexities and unpredictability of human nature coupled with unforeseen challenges and dangers threaten the intrepid pioneers, until only a handful of survivors remain . . . Five thousand years later, their progeny—seven distinct races now three billion strong—embark on yet another audacious journey into the unknown . . . to an alien world utterly transformed by cataclysm and time: Earth. A writer of dazzling genius and imaginative vision, Neal Stephenson combines science, philosophy, technology, psychology, and literature in a magnificent work of speculative fiction that offers a portrait of a future that is both extraordinary and eerily recognizable. As he did in Anathem, Cryptonomicon, the Baroque Cycle, and Reamde, Stephenson explores some of our biggest ideas and perplexing challenges in a breathtaking saga that is daring, engrossing, and altogether brilliant.

With active geysers coating its surface with dazzlingly bright ice crystals, Saturn’s large moon Enceladus is one of the most enigmatic worlds in our solar system. Underlying this activity are numerous further discoveries by the Cassini spacecraft, tantalizing us with evidence that Enceladus harbors a subsurface ocean of liquid water. Enceladus is thus newly realized as a forefront candidate among potentially habitable ocean worlds in our own solar system, although it is only one of a family of icy moons orbiting the giant ringed planet, each with its own story. As a new volume in the Space Science Series, Enceladus and the Icy Moons of Saturn brings together nearly eighty of the world’s top experts writing more than twenty chapters to set the foundation for what we currently understand, while building the framework for the highest-priority questions to be addressed through ongoing spacecraft exploration. Topics include the physics and processes driving the geologic and geophysical phenomena of icy worlds, including, but not limited to, ring-moon interactions, interior melting due to tidal heating, ejection and reaccretion of vapor and particulates, ice tectonics, and cryovolcanism. By contextualizing each topic within the profusion of puzzles beckoning from among Saturn’s many dozen moons, Enceladus and the Icy Moons of Saturn synthesizes planetary processes on a broad scale to inform and propel both seasoned researchers and students toward achieving new advances in the coming decade and beyond.

"What if?" questions stimulate people to think in new ways, to refresh old ideas, and to make new discoveries. In What If the Earth Had Two Moons, Neil Comins leads us on a fascinating ten-world journey as we explore what our planet would be like under alternative astronomical conditions. In each case, the Earth would be different, often in surprising ways. The title chapter, for example, gives us a second moon orbiting closer to Earth than the one we have now. The night sky is a lot brighter, but that won't last forever. Eventually the moons collide, with one extra-massive moon emerging after a period during which Earth sports a Saturn-like ring. This and nine and other speculative essays provide us with insights into the Earth as it exists today, while shedding new light on the burgeoning search for life on planets orbiting other stars. Appealing to adult and young adult alike, this book is a fascinating journey through physics and astronomy, and follows on the author's previous bestseller, What if the Moon Didn't Exist?, with completely new scenarios backed by the latest astronomical research.

A new frontier in our solar system opened with the discovery of the Kuiper Belt and the extensive population of icy bodies orbiting beyond Neptune. Today the study of all of these bodies, collectively referred to as trans-Neptunian objects, reveals them to be frozen time capsules from the earliest epochs of solar system formation. This new volume in the Space Science Series, with one hundred contributing authors, offers the most detailed and up-to-date picture of our solar systemÕs farthest frontier. Our understanding of trans-Neptunian objects is rapidly evolving and currently constitutes one of the most active research fields in planetary sciences. The Solar System Beyond Neptune brings the reader to the forefront of our current understanding and points the way to further advancement in the field, making it an indispensable resource for researchers and students in planetary science.

Few worlds are as tantalizing and enigmatic as Europa, whose complex icy surface intimates the presence of an ocean below. Europa beckons for our understanding and future exploration, enticing us with the possibilities of a water-rich environment and the potential for life beyond Earth. This volume in the Space Science Series, with more than 80 contributing authors, reveals the discovery and current understanding of Europa’s icy shell, subsurface ocean, presumably active interior, and myriad inherent interactions within the Jupiter environment. Europa is the foundation upon which the coming decades of scientific advancement and exploration of this world will be built, making it indispensable for researchers, students, and all who hold a passion for exploration.

The only work to date to collect data gathered during the American and Soviet missions in an accessible and complete reference of current scientific and technical information about the Moon.