A break in planet occurrence near the pebble isolation mass should be observable by the Roman microlensing survey

Abstract

Microlensing detections are uniquely well-suited to probing the population of planets outside the water iceline, down to planetary masses comparable to the Earth. Here, we perform 1D pebble-accretion population synthesis simulations to explore a sample of iceline planets around stars with masses and metallicities similar to the target population of the Galactic Bulge Time-domain microlensing survey of the Nancy Grace Roman Space Telescope. We find that the planet distribution in the microlensing sensitivity space deviates from a log-uniform distribution in mass and orbital radius. When planetary core growth comes to a halt as planets reach the pebble isolation mass, $M_{\mathrm{iso}}$, the combined effects of planetary migration and runaway gas accretion create an occurrence break. Our simulations highlight that, between 1 and 50 AU, the fraction of stars hosting isolation-mass planets (1 to 5 $M_{\mathrm{iso}}$) is lower by a factor 20 compared to less massive planets (0.2 to 1 $M_{\mathrm{iso}}$). If this break in planetary occurrence rates around the pebble isolation mass is detected in future lensing surveys, it would further validate the core accretion paradigm for giant planet formation.

9 pages, 7 figures, accepted for publication in A&A

References in corpus (25)

• Coagulation, fragmentation and radial motion of solid particles in protoplanetary disks
• Separating gas-giant and ice-giant planets by halting pebble accretion
• The Magnetic Fields of Classical T Tauri Stars
• A stellar-mass-dependent drop in planet occurrence rates
• The Exoplanet Mass-Ratio Function from the MOA-II Survey: Discovery of a Break and Likely Peak at a Neptune Mass
• Formation of planetary systems by pebble accretion and migration: How the radial pebble flux determines a terrestrial-planet or super-Earth growth mode
• The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars
• Dust masses of young disks: constraining the initial solid reservoir for planet formation
• The New Generation Planetary Population Synthesis (NGPPS). I. Bern global model of planet formation and evolution, model tests, and emerging planetary systems
• The CARMENES search for exoplanets around M dwarfs -- Planet occurrence rates from a subsample of 71 stars
• Mapping accretion and its variability in the young open cluster NGC 2264: a study based on u-band photometry
• Occurrence Rates of Planets Orbiting M Stars: Applying ABC to Kepler DR25, Gaia DR2, and 2MASS Data
• A stellar mass dependence of structured disks: a possible link with exoplanet demographics
• Microlensing Results Challenge the Core Accretion Runaway Growth Scenario for Gas Giants
• Pebble-driven Planet Formation around Very Low-mass Stars and Brown Dwarfs
• Why do M dwarfs have more transiting planets?
• Microlensing events indicate that super-Earth exoplanets are common in Jupiter-like orbits
• Small Planets Around Cool Dwarfs: Enhanced Formation Efficiency of Super-Earths around M dwarfs
• Disc population synthesis: Decrease in the solid mass reservoir through pebble drift
• Migration and Growth of Protoplanetary Embryos II: Emergence of Proto-Gas-Giants Cores versus Super Earths' Progenitor
• Super-Earth formation in systems with cold giants
• The New Generation Planetary Population Synthesis (NGPPS). VII. Statistical comparison with the HARPS/Coralie survey
• The New Generation Planetary Population Synthesis (NGPPS) VIII. Impact of host star metallicity on planet occurrence rates, orbital periods, eccentricities, and radius valley morphology
• New migration patterns in high planet-star mass ratio systems in disks with low viscosity
• How stellar mass and disc size shape the formation and migration of super-Earths