Solar systems filled to capacity, radio waves over lasers and humanity’s relationship to stardust

Welcome! “Alien Life” tracks the latest discoveries and thoughts in the various elements of the famous Drake Equation. You may notice that this and future entries are shorter than usual; Career, family and book deal commitments have forced me to cut back some of my projects. Now, here’s today’s news:
g Abodes - In this essay, Steven Soter examines computer experiments that simulate the gravitational interactions among planets over billions of years. These models suggest that the solar system is only marginally stable and is dynamically full, or nearly so. Adding another planet between the existing ones would make the system unstable, resulting in a collision or ejection of a planet. See article.
g Life - Philosophers wrestling with the big questions of life are no longer alone. Now scientists are struggling to define life as they manipulate it, look for it on other planets, and even create it in test tubes. See article.
g Message - While advanced civilizations might be tempted to use optical means such as lasers to send information between the stars, there are some good reasons that nearly all the major Search for Extraterrestrial Intelligence experiments are looking for radio waves instead. See article.
g Cosmicus - Quote of the Day: “To place one's feet on the soil of asteroids, to lift a stone from the moon with your hand, to construct moving stations in ether space, to organize inhabited rings around Earth, moon and sun, to observe Mars at the distance of several tens of miles, to descend to its satellites or even to its own surface-what could be more insane! However, only at such a time when reactive devices are applied, will a great new era begin in astronomy: the era of more intensive study of the of heavens.” - Konstantin Tsiolkovsky
g Learning - Are we alone? Are humans unique in the universe, or is our existence the natural outcome of universal processes that produced complex life on Earth and elsewhere? As we observe the universe beyond Earth, we find that we are fundamentally a part of it. To understand the relationship of humanity to stardust requires understanding evolution in its broadest sense. See article. Note: This article on teaching evolution in schools is from January 2001.
g Imagining - The first step in imagining what a real alien might look like is to forget you ever watched the "The X-Files." They won't be the sinister grays Fox Mulder pursues, little green men or even jolly old E.T. And most assuredly they won't look like us. See article. Note: This article is from 1999.
g Aftermath - How might we characterize the political significance of any announcement of discovering extraterrestrial intelligence? How about using the Torino Scale, which characterizes asteroid impacts, as a model to assist the discussion and interpretation of any claimed discovery of ETI? See article.