Revisiting the conundrum of the sub-Jovian and Neptune desert

A new approach that incorporates stellar properties

¹ Dipartimento di Fisica “Ettore Pancini”, Università di Napoli Federico II, Napoli, Italy
² INFN, Sezione di Napoli, Complesso Universitario di Monte S. Angelo, Via Cintia Edificio 6, 80126 Napoli, Italy
³ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
⁴ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁵ Science and Technology Department, Parthenope University of Naples, Naples 80143 Italy
⁶ European Southern Observatory, Karl-Schwarzschild-Strasse 2 85748 Garching bei Munchen, Munchen, Germany
⁷ Fakultat fúr Physik, Ludwig-Maximilians-Universität München, Scheinerstraße 1, 81679 Munchen, Germany
⁸ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Firenze, Italy
⁹ UNESCO Chair “Environment, Resources and Sustainable Development”, Department of Science and Technology, Parthenope University of Naples, Naples, Italy

^★ Corresponding author; christian.magliano@unina.it

Received: 25 June 2024
Accepted: 18 November 2024

Abstract

Context. The search for exoplanets has led to the identification of intriguing patterns in their distributions, one of which is the so-called sub-Jovian and Neptune desert. The occurrence rate of Neptunian exoplanets with an orbital period P ≲ 4 days sharply decreases in this region in period-radius and period-mass space.

Aims. We present a novel approach to delineating the sub-Jovian and Neptune desert by considering the incident stellar flux F on the planetary surface as a key parameter instead of the traditional orbital period of the planets. Through this change of perspective, we demonstrate that the incident flux still exhibits a paucity of highly irradiated Neptunes, but also captures the proximity to the host star and the intensity of stellar radiation.

Methods. Leveraging a dataset of confirmed exoplanets, we performed a systematic analysis to map the boundaries of the sub-Jovian and Neptune desert in the (F, R_p) and (F, M_p) diagrams, with R_p and M_p corresponding to the planetary radius and mass, respectively. By using statistical techniques and fitting procedures, we derived analytical expressions for these boundaries that offer valuable insights into the underlying physical mechanisms governing the dearth of Neptunian planets in close proximity to their host stars.

Results. We find that the upper and lower bounds of the desert are well described by a power-law model in the (F, R_p) and (F, M_p) planes. We also obtain the planetary mass-radius relations for each boundary by combining the retrieved analytic expressions in the two planes. This work contributes to advancing our knowledge of exoplanet demographics and to refining theoretical models of planetary formation and evolution within the context of the sub-Jovian and Neptune desert.