Looking beyond carbon in astrochemistry

Terrestrial planets like Earth form when interstellar dust coalesces to form a rocky core. Though much of Earth’s crust is made up of inorganic minerals rich in elements such as oxygen, aluminum, and magnesium, the molecular origins of these rocky, planet-building blocks are not well understood compared to carbon-based compounds, said Ryan Fortenberry, an astrochemist at the University of Mississippi. “How do we get from [atoms to] very small rocks all the way to very big rocks, like the Earth on which we stand?” he said.

To address this gap, Fortenberry and his colleagues are developing computer simulations to investigate how small inorganic molecules might react in early planetary systems. During a talk in the Division of Physical Chemistry at ACS Fall 2022 on Tuesday, Fortenberry reported calculations predicting that water and aluminum hydride, called alane, can react to form a variety of molecules, including Al₂O₃H₆. This hydrogenated aluminum oxide is a monomer of corundum, a common mineral on Earth that forms rubies and sapphires (ACS Earth Space Chem. 2022, DOI: 10.1021/acsearthspacechem.1c00324).

When Fortenberry and his team simulated the vibrational spectra of this compound and others proposed by their work, they found that these molecules would likely produce strong signals in mid-to-far-infrared wavelengths. These signals fall outside the range typically used to study carbon-based compounds in space, but should be detectable with instruments on the recently launched James Webb Space Telescope. Fortenberry hopes his team’s findings will motivate astrochemists to look for these signals to better understand how planets form from small inorganic molecules.