Emerging Trends in a Period-Radius Distribution of Close-in Planets

TL;DR

This paper investigates the distribution of close-in exoplanets in terms of their orbital periods and radii, revealing notable gaps and trends linked to stellar metallicity that could inform planetary formation theories.

Contribution

It identifies a new 'sub-Jovian Pampas' region with a scarcity of planets, and analyzes how metallicity influences planet distribution, providing novel insights into planetary demographics.

Findings

Evidence for a 'sub-Jovian Pampas' with few planets (3-10 R_⊕, P<2-3 days)

Metal-poor stars lack small planets with P<5 days

Metal-poor stars also lack sub-Jovian planets with P<100 days

Abstract

We analyze the distribution of extrasolar planets (both confirmed and Kepler candidates) according to their orbital periods P and planetary radii R. Among confirmed planets, we find compelling evidence for a paucity of bodies with 3 < R < 10 R_\oplus, where R_\oplus in the Earth's radius, and P < 2-3 days. We have christened this region a "sub-Jovian Pampas". The same trend is detected in multiplanet Kepler candidates. Although approximately 16 Kepler single-planet candidates inhabit this Pampas, at least 7 are probable false positives (FP). This last number could be significantly higher if the ratio of FP is higher than 10%, as suggested by recent studies. In a second part of the paper we analyze the distribution of planets in the (P,R) plane according to stellar metallicities. We find two interesting trends: (i) a lack of small planets (R < 4 R_\oplus) with orbital periods P < 5 days in metal-poor stars, and (ii) a paucity of sub-Jovian planets (4 R_\oplus < R < 8 R_\oplus) with P < 100 days, also around metal-poor stars. Although all these trends are preliminary, they appear statistically significant and deserve further scrutiny. If confirmed, they could represent important constraints on theories of planetary formation and dynamical evolution.