Finding alien worlds is an idea older than science-fiction itself. The problem is how planets are exceptionally difficult to spot at the best of times, what with being small dull rocks insanely far away, never mind their nasty habit of hanging around incredibly bright radiation sources which swamp sensitive detection gear - or as we would call them, “stars.” Now a team have found an easily observed stellar signature indicating the presence of exoplanets.
The key is lithium. A stellar spectography survey of over five hundred stars reveals that known-planet-bearers, including our own Sun, have less than a hundredth of the lithium of “barren” stars. Stars don’t produce much lithium in their fusion reactions, so most share the same proportion of the element, which was created at the beginning of the universe. But some stars seem to destroy their stock, fusing it into other elements, and a European team have found that they all have one thing in common: planets.
Exactly how this happens is another matter. It seems insane that something as small as a planet could dramatically affect the composition of a star, but the key point is that lithium destruction depends on convection currents in star’s upper layers - and those can conceivably be altered by orbiting bodies. Deeper convection can carry lithium from the cooler outer layers towards the core, where increasing temperature and pressure force fusion. There are a number of different models and phenomena to take care of the details, and that’s sure to be an active area of research now that we’ve engaged full scientific “We’re sure it happens, now how does it happen” mode.
The really exciting aspect is just how identifiable this makes planetary systems. Instead of observing minute wobbles or tiny dips in the data, spectrographic examination means we can detect the lithium levels just be looking at the light shining from the star. And shining light is stars’ entire deal.
Luke McKinney
Exoplanets Clue To Sun’s Curious Chemistry
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