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.

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