The study of exoplanets is another great way to find out everything you knew about science, in particular planetary formation and evolution, was wrong. When your sample set includes a solar system of one, you begin to think, “Other solar systems must be similar.” And then you put up a telescope or two, find thousands of exoplanets, and discover, “Huh. It’s wilder out there than we imagined.”

Such is the case with exoplanet LHS 3844b, a small, rocky planet, slightly bigger than Earth. It’s tidally locked, like Mercury. It has no atmosphere, like Mercury. And then everything goes sideways. LHS 3844b always has the same side facing its star, so the planet’s surface can reach 770°C on the dayside and near absolute zero on the nightside. Not only that but in research presented this week at AGU’s Fall Meeting, researchers explained how they used those surface temperatures to find that the planet’s mantle could flow in a half-and-half pattern. Basically, it flows upward on one side and downward on the other.

They used simplified models to test several convection scenarios, varying the strength of the lithosphere material between very weak and strong but still pliable. Lead researcher Tobias Meier goes on to explain: We also vary the heating mode wherein one set of models we have basal heating, which means that all the heat that we generate comes from within the core. And in a second set of models, we also add internal heating to that, which means that we generate heat within the mantle that could come, for example, from the decay of radioactive elements.

They found that three of the models produced the half-and-half hemispheric scenario, while only one model – with stronger material and internal heating – produced Earth’s version of a mantle. So while LHS 3844b is the first exoplanet we’ve found without an atmosphere, it’s also the first one we’ve modeled with this mantle convection pattern.

Computational geodynamicist Rene Gassmoeller further explains: Since these conditions are very strict, it is unlikely any planets in our solar system fulfilled them at any point in the history of the solar system. Mars is too far out. Earth and Venus have atmospheres and are not tidally locked. Mercury is tidally locked, but not in a synchronous rotation, so all surface locations still experience day and night.

As always, we have found more pieces to the solar system formation puzzle. We’re not even close to done, yet.

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