Nêmesis (mais ou menos) ressuscitada

Um estudo publicado recentemente por um físico teórico da Universidade da Califórnia e um astrônomo do Instituto Max Planck aponta para a conclusão de que praticamente todas as estrelas são ao menos binárias nos momentos iniciais de sua formação. Depois, algumas perdem suas companheiras iniciais e outras, não. Leia a notícia publicada no Universe Today aqui.

Se o estudo estiver correto, provavelmente o Sol teve uma irmã gêmea em sua infância, perdida desde então. Como o artigo lembra, isso é vagamente reminiscente da velha ideia de que o Sol deve ter uma companheira estelar, convenientemente chamada de Nêmesis. A ideia não vingou mas tem seu charme.

Por que o estudo é importante? Porque, entre outras coisas, a ideia de um Sol resultando de uma formação de um sistema inicial binário pode ter repercussões sobre as teorias de formação do sistema solar, que geralmente não levam em consideração essa possibilidade.

Formação planetária ainda é nebulosa

Como o sistema solar surgiu? Como se formam os sistemas planetários? Ninguém sabe. Ou, sendo menos pessimista: a situação das explicações atuais é, no mínimo, nebulosa. Notícia de 2011 da National Geographic dá uma ideia do mato sem cachorro em que se encontra o campo das teorias de formação de sistemas planetários. Recomendo a leitura pra quem acha que a hipótese nebular de Laplace está firme e forte desde o fim do século XVIII.

Sobre os modelos atuais rodados em simulações de computador, Hal Levison, um teórico da formação planetária, disse algo super animador:

“The only thing we can say for sure is that those models don’t work. […] Those are crappy models.”

Mercúrio e nossas origens

Na Atlantic, um artigo pequeno mas muito bacana sobre Mercúrio. O discreto planeta pode ser importante para que as ciências consigam pistas sobre a formação do sistema solar e a própria origem da vida.

When Mariner 10 arrived at Mercury 40 years ago, it found that the little rock, unlike Mars and Venus, generates its own internal magnetic field. Mercury also has plate tectonics like the Earth, but rather than many plates, it has one massive plate cracking and contracting above its liquid outer core. “That puts Mercury in a special place with the Earth,” said Tom Watters, senior scientist at the Center for Earth and Planetary Studies of the Smithsonian National Air and Space Museum. “The two bodies are tectonically active today with active magnetic fields … there’s no evidence that either Mars or Venus have active tectonics.”

There’s a reason for Mercury’s magnetic field. Its iron innards take up over 80 percent of its radius, or more than 60 percent of its volume. The Earth’s core, for comparison, only takes up a little over half its radius, less than a third of its volume. That means Mercury is a dense metal sphere—a lot more metal than rock, said Solomon. So scientists wondered: How do planet formation processes create a mostly metal ball? They had a few theories: Maybe Mercury formed in a metal-rich region around the Sun, or maybe the early Sun blasted some outer layer of rock away. Or, the most badass theory, maybe Mercury was once the size of Mars and took a major wallop from some giant unknown visitor, stripping away part of its diameter. None of these theories turned out to be correct. When MESSENGER arrived, the planet revealed way more volatile elements, those with low boiling-points like sulfur or potassium, than scientists expected to see. Any of the above scenarios would have vaporized these materials off of the planet, and yet they remained.

Mercury has been generous with the secrets of the solar system’s other planets, including our own, thanks to deposits of water ice hiding at its poles. Despite sitting a mere 36-million miles from the Sun on average, it has some valleys hiding in the shadows forever, staying frigid without radiation exposure, or an atmosphere to distribute the heat. That’s where the water ice hides, covered in dark splotches that scientists like David Paige at the University of California, Los Angeles haven’t confirmed, but have reason to believe, is carbon.

If these dark splotches are carbon, then the dark craters might even help explain how we ended up with life here on Earth. Scientists believe that much of our own carbon and water came from the outer reaches of the solar system, said Solomon. Those craters could contain the oldest samples of some of the carbon and water that eventually let you, a carbon-based organism, sit down and read this piece today. As some of the oldest undisturbed carbon samples in the solar system, they’d allow us to look at the earliest carbon and water looked like on our own planet. “It’s a little bit bizarre in a way,” said Solomon. “We might have to go to Mercury to address the question of how life might have started on our own planet.”

So understanding one of the most important secrets of our own planet relies on sending a lander to a tiny, atmosphere-less, scorching metal ball, sending the craft circling the inner solar system for several years just to stick it into orbit. Mess anything up and the craft shoots directly into the Sun.

Kant e o universo-fênix

The push and pull of the bond explains cosmic self-organization, and in the Universal Natural History Kant shows how the chaos evolved to the starry skies visible now. It should be possible to do the same for organisms, but science at the time did not explain the formation of life. How life unfolds we do not know (1:230.14–20); we only know that it does. Kant believes (science agrees) that star birth is easier to determine than the creation of life (1:230.20–26).

With his famous nebular hypothesis, Kant discerned how planets, stars, and galaxies form. Their birth is a process of titanic power. Attractive forces contract particles into clouds, but repulsive forces deflect them up close. Continued accretion increases deflection, imparting angular momentum on the ever quicker rotating cloud. Rotation generates centrifugal forces, pulling the cloud’s equators outwards, crushing the poles, until the out-bulging yet in-falling sphere, revolving ever faster around its center, flattens into a disc. The bond, in Newton’s model of universal gravitation, continues coalescing in momentum and spin, until the center of the cosmic disc is so energized that it combusts. Increased energy translates into increased structure, organizing the ecliptic plane into lumpy coalescence. When the disc plane sediments into spinning bands, the lumps grow massive, while caroming along their orbits. The moving masses vacuum their paths and grow into planets strung along an ecliptic plane, orbiting a sun in now empty space—or, on a higher order of magnitude, into suns majestically revolving around a brightly lit galactic center. Whether suns in spiral galaxies, or planets in solar systems, the orbiting satellites sweep out equal areas in equal times, with their periods in sync with their distances from the gravitational centers.[18]

With this essay, Kant synthesize Newton with his own theory of forces, leading Kant to the cutting edge of current knowledge. Nature, in the Universal Natural History, streams outward in a wavefront of organization (1:314.1–2), generating worlds (1:314.8), biospheres and sentience (1:317.5–13, 352–3), and finally reason, human and otherwise (1:351–66). Organization is fragile, and spontaneity, pushed far enough, invites chaos. Mature cosmic regions decay, chaos sets in, and entropy follows in the wake of complexity. But entropy provides the very conditions that allow the cosmic pulse to bounce material points back to order. Thus the expanding chaos coalesces at its center into order, followed by chaos, by order, by chaos. Like a rising and burning phoenix, nature cycles between life and death (1:312.13).

For creatures, the cosmic phoenix is a problem. Humans are just feathers on its wings. Humans grow only to burn to ashes; they are not exempt from the cosmic law (1:318.17–18). As the pulsing cosmic vector governs everything, order emerges on all orders of magnitude, from the repetitive birth of the phoenix to the elements to life and to inevitable collapse—only to begin anew again. The force-space bond unfolds in the interactive harmony of dynamic opposites, an interaction governed by Newton’s universal gravitation, churning out galaxies, suns, planets, life, and minds. Thus, as Kant writes, a “single universal rule” guides natural evolution in an absolutely glorious way (1:306.18–23).