Gap in the Solar System’s Proto-Planetary Disk Is Further Evidence Confirming Similarly Located Gap in the Distribution of Exoplanet Semi-Major Axes

The recent discovery of a gap dividing the solar system’s protoplanetary disk (SS’s PPD) into two peaks is further evidence of a similarly located gap in the distribution of exoplanet semi-major axes a. This Peak-Gap-Peak (PGP) feature is found in the distribution of a of exoplanets hosted by the single stars that have roughly solar mass (under 0.8 to over 1.2 M_sun), and have the same or higher metallicity than the sun. The exoplanet PGP feature has been published before the presentation of the gap in the SS’s PPD. This gap is present for planets of single stars, but appears partially filled for planets of stars with stellar companions. It might be expected that a stellar companion induces migration that would remove features. The gap in the solar system’s PPD is reported to be closer than 3 AU, while for exoplanets of solar-mass stars the gap in exoplanet a extends from the end of an inner peak at 1.5 AU to a well-defined sudden dramatic pileup starting at 1.9 AU. We are now reporting finding that the semi-major axis of this feature appears to scale with the square root of stellar mass.

The two results taken together suggest that planets of stars that are similar to the sun or with higher metallicity may generally start their evolution with a gap in this range, likely associated with a snow line. Recent observations evidence a snow-line closer to 2 AU.

To best promote study of features of the distribution of exoplanets, we propose that the study of planetary system architectures and demographics be organized in the form of a new additional section of an exoplanet catalog, which would include results on exoplanet occurrence distributions and findings of features and correlations among exoplanet parameters.