Split Peas in a Pod: Intra-system Uniformity of Super-Earths and Sub-Neptunes

The planets within compact multi-planet systems tend to have similar sizes, masses, and orbital period ratios, like "peas in a pod". This pattern was detected when considering with radii between 1 4 $R_\oplus$. However, these same show bimodal radius distribution, few 1.5 2 $R_{\oplus}$. smaller "super-Earths" are consistent being stripped rocky cores, while the larger "sub-Neptunes" likely gaseous H/He envelopes. Given distinct structures, it is worthwhile test for intra-system uniformity separately each category of planets. Here, we find that tendency twice as strong size than combining all together. sub-Neptunes be $1.7^{+0.6}_{-0.3}$ times super-Earths system, corresponding an envelope mass fraction about 2.6% $5\,M_{\oplus}$ planet. For sub-Neptunes, low-metallicity stars found more equal modest statistical significance ($p\sim 0.005$). There also $(\sim$2-$\sigma)$ wider-orbiting larger, even category.