CapitalistImperialistPig

Mike Brown's penultimate lecture in his Caltech/Coursera Solar System course concerns what he calls "the best experiment to find life in the Solar System" yet. On it's trip to Jupiter, the Galileo spacecraft flew by a couple of planets to get a slingshot boost on its way, taking some data in the process. The data consisted of infrared spectra, imagery at multiple filtered wavelengths, and radio data. Some of the data was highly suggestive: oxygen in the atmosphere, presence of liquid water, very abundant methane in the atmosphere, and some peculiar features in the wavelength filtered data. All of the above were suggestive of the presence of life, but hardly conclusive. You have perhaps guessed the identity of the planet in question: Earth. The data, analyzed by Carl Sagan and colleagues, also included imagery with a resolution of roughly 1 kilometer. No definitive signs of human construction were found at that scale. The only definitive evidence of life, and...

And there is a chance one might kill you! An extremely unlikely chance, says Mike Brown. About 1 in 74 million, meaning that there are 73,999,999 other ways that are equally likely to knock you off. Of course the occasional biggie can flatten a city or even a continent, but Brown says we know there aren't any of the continent smashers headed our way for at least several hundred years. Consequently, there is no urgency whatsoever to rush to build a zillion dollar asteroid defense system. We should continue to study asteroids, mainly for other reasons, but just monitor the situation. If one is headed here in 500 years, we can hope that our descendants will be a lot better prepared to deal with it then. Comets are another problem. Partly because they are moving much faster, so they have a lot more kinetic energy. Mostly, though, the problem is that we won't have, can't have, much warning. A year or two at most. Consequently, our prospects for doing anything about a...

So far as we know, Mars never had any flowers, but it did have water, and fair amounts of it, at least for a while. My current favorite MOOC is Mike Brown's Caltech Solar System class via Coursera. The first third of the course is devoted to Mars, and it's fascinating. The oldest terrain on Mars, called the Noachian, shows evidence of rain, flowing streams, and lakes. There are also lots of craters, suggesting that this may have occurred during the so-called Late Heavy Bombardment. Not a whole lot of rain, but something comparable to the deserts and semi-deserts of modern Earth. Obviously this would have required a warmer and wetter Mars than that of today. How could it have been that warm, especially with the Sun perhaps 70% as bright as today? The most plausible answer is greenhouse gas, probably mostly CO2, supplemented by some water vapor. After a few hundred millions of years, by the Hesperian period, evidence of rain goes away, but evidence of water doesn't...