Why metal-rich stars host more gas giants
The frequency of gas giants is strongly tied to the amount of solid material available in the planet-forming disk, which astronomers measure as metallicity—the abundance of elements heavier than hydrogen and helium. A 2024 study of 184 super-Earth systems found that the conditional probability of an outer gas giant given an inner super-Earth is 28% for metal-rich stars but only 4.5% for metal-poor stars [1]. This means that around metal-poor stars, gas giants are genuinely uncommon in systems that also have super-Earths.
The same study compared these conditional rates to field giant occurrence rates and found a distinct positive correlation between inner super-Earths and outer gas giants for metal-rich hosts, but this correlation disappears for metal-poor systems [1]. The authors interpret this as evidence that metallicity—the disk's solid budget—plays a critical role in shaping the overall planetary architecture [1].
Where gas giants sit changes how often they appear
Gas giant frequency also depends on orbital distance. A 2022 study modeling the period distribution of gas giants inside 300 days found that a bimodal model based on snowlines—special locations where ices condense—fits the observed data better than a simple linear distribution of planetary seeds [4]. This suggests that gas giants form preferentially at particular locations rather than uniformly across the disk, which means their occurrence rate varies with orbital period.
The 2024 super-Earth study adds that around metal-rich stars, the correlation with outer gas giants is slightly enhanced for systems with giants beyond 3 au, more eccentric giants (e > 0.2), and multi-gas-giant systems [1]. So even among metal-rich stars, gas giants are more likely to be found in certain orbital configurations than others.
Do gas giants help or hinder small planets?
Gas giants may influence where small planets end up. A 2015 simulation study showed that gas giants can act as dynamical barriers, blocking inward-migrating super-Earths, and suggested that gas giants should be rare in systems with hot super-Earths [5]. This is a proposed dynamical effect, not a direct measurement of occurrence rates, but it implies that the presence of a gas giant could change the architecture of a planetary system.
More recent work hints at a subtler connection. A 2026 study of 43 systems with inner small planets found no significant difference in gas giant occurrence rate based on small-planet density, envelope mass fraction, or core mass overall, but saw hints that in metal-rich systems, gas giants are preferentially found with lower-density planets of similar core mass [2]. The authors caution that small sample sizes limit these trends, and they interpret the hints as consistent with metal-enriched disks catalyzing rapid core assembly and early gas accretion [2].
Survival during migration adds another filter
Even when gas giants form, their long-term survival depends on orbital dynamics. A 2026 paper on tidal migration found that inertial waves may help gas giants survive high-eccentricity migration, unlike their Neptunian counterparts [3]. This is an indirect clue about frequency: if gas giants can survive processes that might otherwise destroy them, then some orbital contexts may retain more gas giants than would otherwise be expected. However, the abstract does not provide occurrence rates, so it does not directly answer how rare gas giants are.
Sources used in this answer
Friends Not Foes: Strong Correlation between Inner Super-Earths and Outer Gas Giants
In super-Earth systems, outer gas giants occur in about 28% of metal-rich hosts but only about 4.5% of metal-poor hosts, showing a positive correlation between inner super-Earths and outer gas giants only for metal-rich stars.
An early look at how gas giants shape small planet bulk compositions
Gas giant occurrence rates in systems with inner small planets show no significant overall trend with small-planet density, envelope mass fraction, or core mass, but hints in metal-rich systems suggest gas giants may preferentially accompany lower-density planets of similar core mass.
The Neptunian Final Parsec Problem: How Inertial Waves Enable Neptunes and Gas Giants to Survive Tidal Migration
Inertial waves may enable gas giants to survive tidal migration, unlike Neptunes, providing an indirect clue about their survival in certain orbital contexts.
The origin of the occurrence rate profile of gas giants inside 100 days
The period distribution of gas giants inside 300 days is better fit by a model where planets form preferentially at snowline locations than by a linear distribution of seeds.
Gas Giant Planets as Dynamical Barriers to Inward-Migrating Super-Earths
Dynamical simulations suggest gas giants can block inward-migrating super-Earths, implying that gas giants should be rare in systems with hot super-Earths.