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...

Red dwarfs, or M-dwarfs, are the most common type of star as well as the smallest and dimmest main-sequence (hydrogen burning) stars. Because of their low luminosity and because many of them are fully convective and hence can burn a large fraction of their total hydrogen, they are very long lived, in many cases hundreds of times longer than our Sun. These trillion year lifetimes are much longer than the present age of the universe. Because they are so common, and because their small size makes it relatively easy to observe transits of their exoplanets, they are a favored place to look for Earthlike planets. Such planets would have some funky properties. If they are in the habitable zone, the zone where temperatures permit liquid water to exist on planetary surfaces, they would be tidally locked to their star, keeping one face always toward it. Despite their dimness, red dwarf stars have a great deal of magnetic activity, and their titanic solar storms bombard their planets with ...

Or, at least, less than 100. We know that, says Mike Brown, because the level of methane on Mars is less than 1 part per billion - about the amount that would be produced by 100 cows, burping. It's not exactly a shock that Mars is not prime cattle country, but the aforementioned result is also a major blow to one of Mike's favorite theories: that some kind of life on Mars was all but certain since life from Earth was very likely transported to Mars in the Early days by meteorites blown off the Earth in major collision, to land there when the planet was more hospitable. Even today, it seems likely that Mars has locales where methanogens would survive and reproduce. Of course the reverse voyage scenario is also possible. In which case it would be a bit tragic that the planet that (perhaps) gave us birth, no longer supports life.

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...

The equations of motion that govern the Solar System are chaotic . So a kind of important question is that of whether planetary orbits are stable. The best available answer seems to be maybe. When simulations are run for a few billion years, some funky stuff sometimes - but only rarely - happens. Sometimes Mercury collides with Venus. Sometimes with the Sun - or, more usually, neither. Sometimes Mars gets ejected from the Solar System. Gravitational micro-lensing observations seem to show that there are a certain number of orphan planets out there, planets that apparently formed in stellar systems but subsequently hit the road after getting ejected from their birth systems. There are even hints that such an event might have occurred early in the history of our Solar System. One puzzling event of early solar system history is the so-called Late Heavy Bombardment. One theory sanctioned by dynamic simulation is that this asteroid bombardment, some 300-500 million years after...

The metallicity of a star, we might recall, measures how much of its material consists of elements heavier than hydrogen and helium, that is, those elements that were manufactured in earlier generations of stars that subsequently spewed their contents across the cosmos. Our Sun, for example, has about 1 iron atom for every 20,000 hydrogen atoms. Metallicities of other stars are measured on a logarithmic scale on which the Sun is defined to have metallicity zero. Thus, a star with metallicity -4 has an iron fraction only 1/10000 that of the Sun (1 iron atom for every 200 million hydrogen atoms). The most metal poor stars of all seem to have metallicities of about -4.5, while the most metal rich are near 1, with ten times more iron than the Sun. Since the very first generation of stars had no metals at all, these would have been off the scale in the negative direction, but none of these so-called Population III stars seem to have survived to the present. The kinds of planets a st...

It seems that the hottest prospects for extraterrestrial life in the solar system may be two icy moons, Jupiter's Europa and Saturn's Enceladus.  Both appear to be covered by an icy surface that seems to recycle itself fairly frequently.  Both appear to be heated by tidal forces due to their gas giant mother planets and other moons.  It's at least plausible that there is an ocean of liquid water under all that ice. Enceladus made a big push for the number one spot by spouting some vapor plumes near its South Pole.  The Cassini probe was able to fly through the plume and measure water vapor, carbon compounds and other cool and suggestive stuff.  Of course Cassini wasn't actually designed for that kind of work so the most fascinating organic clues lie beyond our reach - for now. Europa is a bit larger than Earth's Moon, but Enceladus is tiny, only 500 or so in diameter.