Doing Exoplanet Chemistry From Earth

Exoplanets are light years away, hidden by their parent stars, and barely detectable.  Yet even though most have never been directly imaged, we can study the light from the parent star as the planet passes in front of it, and use this information to learn about the planet’s size and composition, especially if it has an atmosphere.  Once you know a little bit about how big and dense a planet is, and the major elements that form it’s crust and atmosphere, you can do a lot of Chemistry to figure out what it should be made of and how these molecules behave.

Earth vs. a typical Super-Earth planet

Earth-like planets are all based on the same main elements: Silicon, Oxygen, and Magnesium.  These three elements form the basis for the crust, which is the largest part of one of these planets by volume.

Because these super-Earth planets are much larger and heavier than Earth, the elements are subject to much greater pressures below the surface.  Knowing this, chemists have used computer models to simulate the various combinations of these three elements for the conditions on super-Earth exoplanets.  On Earth, the common MgSiO3 may be replaced by the more exotic MgSi3O12 and MgSiO6.  Many of these molecules are metals or semiconductors, very different from the Mg-Si-O combinations found on Earth.  With more semiconductors and metals in the crust, a planet could have a very strong magnetic field.  If we could measure such a magnetic field on a distant exoplanet, it could prove the existence of these rare compounds.

A stronger magnetic field is considered to be very favourable for life as it evolves, since it can shield a planet from the dangerous radiation released by a star.  We already know that life can survive under harsh conditions, including the crushing pressures seen at the bottom of the ocean.  Strong magnetic fields are a necessary criteria in narrowing down the search for alien life, as far as we know.

So there it is, the power of the scientific method! We can use what we know about chemistry and gravity, use our advanced technology, and come up with very strong hypotheses about the chemistry and behavior of other worlds.  The interconnectedness of nature is staggering and can lead us to some truly ingenious ways of probing the universe.

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