The mysteries of how exoplanets formed are always intriguing scientists, but there is another enigma in space that has the potential to fascinate us just as much as any alien planet—and we live on it.
Exoplanets can tell us a galaxy of secrets through their orbital parameters and their planet’s host star. At least for a moment, a research team from the Australian National University put the exoplanets on hold and reversed those methods to really zero in on Earth. What emerged from this study was the most accurate estimate of our planet’s elemental composition, something that has been confounding scientists for years. It also illuminated more about how Earth formed, things that have stayed in the dark for 4.6 billion years.
While Earth is mostly a conglomeration of iron, oxygen, silicon, and magnesium, which make up more than 90% of its mass, what has been eluding scientists is exactly what sorts of things smashed into each other and accreted billions of years ago to create this planet. The team used the same transit photometry and radial velocity measurements they usually apply to estimating exoplanet density and minerology.
“The idea is that rocky planets orbiting their host stars are devolatilized pieces of their host stars,” said Charley Lineweaver, associate professor at the Australian National University’s Planetary Science Institute. “Since the processes of devolatilization, sublimation, and evaporation are dominated by the universal properties of atoms and molecules, then the effects of these processes could be similar everywhere in the universe.”
Devolatalization involves removing all volatile organic compounds (VOCs), which easily vaporize or turn to gas. By factoring out VOCs in an unprecedented experiment, the scientists were able to produce an optimal model of Earth’s elemental composition and then compare that to the best model showing the elemental composition of the sun.
Previously, Earth scientists had done pretty much everything but use devolatilization to figure out what is really underneath our feet. There have been studies on everything from the elemental composition of the mantle to that of the core, with a worrying absence of error bars, which tell how precise or imprecise a measurement might be by gauging the level of uncertainty in measurements. That sparked something else unexpected.
“To combine the elemental compositions of the mantle and the core, one crucially needs to know the mass fraction of the core,” Lineweaver explained. “This number tells you how much of the core’s elemental composition you have to add to the mantle’s composition. The core mass fraction has been estimated, but no one had gone to the trouble of estimating the uncertainty on that fraction.”
Earth was found to have significantly lower levels of certain elements than previous studies had found and higher levels of those that were thought not to be so abundant. Think less magnesium, tin, bromine, and cadmium but more sodium, potassium, and chlorine. Being able to obtain the most realistic uncertainties possible not only furthers our understanding of Earth, but also opens a portal to comparing our planet with Mars, the sun, or really, anything else floating around in the solar system, and eventually bodies in faraway star systems.
Could this mean that we could eventually find an exoplanet whose elemental composition is eerily close to Earth’s? Maybe, but that still doesn’t mean aliens.