Mass constraints for the K2-223 system planets: An ultra-short-period sub-Earth, a short-period super-Earth, and a tentative long-period giant planet

@misc{jankowski2026mass,
  title = {{Mass constraints for the K2-223 system planets: An ultra-short-period sub-Earth, a short-period super-Earth, and a tentative long-period giant planet}},
  author = {Dawid Jankowski and Grzegorz Nowak and Gaia Lacedelli and Enric Pallé and Krzysztof Goździewski and Thomas Masseron and Ilaria Carleo and Rafael Luque and Felipe Murgas and Davide Gandolfi and Artie P. Hatzes and William Cochran and Pedro Figueira and Rafael A. García and Samuel Geraldía-González and Judith Korth and Pierrot Lamontagne and John H. Livingston and Savita Mathur and Giuseppe Morello and Jaume Orell-Miquel and Dinil B. Palakkatharappil and Carina M. Persson and Seth Redfield and Atanas K. Stefanov and Vincent Van Eylen},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.01721},
  eprint = {2609.01721},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.01721},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Mass constraints for the K2-223 system planets: An ultra-short-period sub-Earth, a short-period super-Earth, and a tentative long-period giant planet
AU  - Dawid Jankowski
AU  - Grzegorz Nowak
AU  - Gaia Lacedelli
AU  - Enric Pallé
AU  - Krzysztof Goździewski
AU  - Thomas Masseron
AU  - Ilaria Carleo
AU  - Rafael Luque
AU  - Felipe Murgas
AU  - Davide Gandolfi
AU  - Artie P. Hatzes
AU  - William Cochran
AU  - Pedro Figueira
AU  - Rafael A. García
AU  - Samuel Geraldía-González
AU  - Judith Korth
AU  - Pierrot Lamontagne
AU  - John H. Livingston
AU  - Savita Mathur
AU  - Giuseppe Morello
AU  - Jaume Orell-Miquel
AU  - Dinil B. Palakkatharappil
AU  - Carina M. Persson
AU  - Seth Redfield
AU  - Atanas K. Stefanov
AU  - Vincent Van Eylen
PY  - 2026
DA  - 2026/09/16
PB  - arXiv
DO  - 10.48550/arxiv.2609.01721
UR  - https://arxiv.org/abs/2609.01721
AB  - We present mass constraints of two short-period Earth-sized planets transiting K2-223 based on high-precision radial velocity measurements from HARPS-N and ESPRESSO, as well as a tentative indication of an outer Jupiter-like planet orbiting the G1V dwarf K2-223. With a radius of R_b=0.79±0.10 R_⊕ and a 3σ upper mass limit M_b<2.8 M_⊕, K2-223 b belongs to the small group of known sub-Earth planets and is currently the smallest known ultra-short-period planet (P_b≈ 0.5 day) transiting a solar-type star. With a radius of R_c=1.41±0.15 R_⊕, a mass of M_c=4.2±1.3 M_⊕, and a density of ρ_c=8.3±3.7 g cm^−3, K2-223 c is a short-period (P_c≈ 4.5 days) super-Earth. Based on almost 6.5 years of radial velocity monitoring of K2-223 with the HARPS-N spectrograph, we identified a tentative giant planet with an orbital period of P_d=4.53^+0.32_−0.34 years and a minimum mass of 1.29^+0.23_−0.17 M_Jup. Two close-in small planets accompanied by a distant candidate Jupiter-like companion would make K2-223 a system with a rare architecture. This is valuable for testing scenarios of planetary formation and evolution. The extreme proximity of K2-223 b to the parent star means that relativistic and tidal perturbations to Newtonian gravity need to be considered. We discuss the timescales and amplitudes of these effects in the context of the radial velocity model and dynamical simulations of the K2-223 multiple-planet system. We also present a parametrisation of the planets with directly measured masses, radii, and bulk densities in terms of the orbital period normalised by the Roche period. This provides an alternative representation in the context of the Neptune desert.
ER  -