A paper by graduate student Armaan Goyal, titled “Peas-in-a-Pod across the Radius Valley”, has recently been accepted for publication in the Astrophysical Journal Letters!
Planets smaller than 4 times the size of the Earth represent the most common type of exoplanet in the Milky Way, meaning that the study of this specific population can shed tremendous light on how planets and planet systems form and evolve in general!
This important group of exoplanets is itself characterized by two very striking trends. The first of these is the “peas-in-a-pod effect“, for which planets orbiting the same star tend to be extremely similar in their mass, size and spacing. The other is the existence of the “radius valley”, which suggests that small planets (less than 1.6 times the size of the Earth) are mostly made of solid, rocky material, while intermediate-sized planets (between 1.6 and 4 times the size of the Earth) are likely to contain more volatile (liquid or gaseous) compounds!
Armaan’s paper presents a unique assessment of this exoplanet population through a combined lens of these two trends, specifically asking the question: is the uniformity of an exoplanet system as a whole tied to the composition of its individual planets? Applying a variety of statistical tests to over a hundred systems from the California Kepler Survey and NASA Exoplanet Archive, Armaan’s work finds that systems with only rocky planets are more uniform in size and spacing, but less uniform in mass, than systems containing only volatile-rich worlds. Armaan also finds that these trends for rocky planets break down if the planets themselves are smaller than the size of the Earth.
Armaan’s results uncover intriguing links between the structure of entire exoplanet systems and the makeup of their individual worlds, the likes of which place new constraints on not only planet formation at its smallest and largest scales, but perhaps the origins of our own solar system as well.
This work was conducted in collaboration with IU’s own Professor Songhu Wang. The full paper can be found at:
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