Uncovering temperate worlds: an updated look at the K2-3 system with ESPRESSO
Abstract
The K2-3 system is one of the most unique planetary systems as it features three transiting sub-Neptunes in decreasing order of radii, spanning the radius valley. In addition to that, the two outer planets are temperate in nature making this system a perfect laboratory for investigating the nature and formation of small potentially habitable worlds. We present new radial velocity data obtained during the ESPRESSO-GTO programme to add to the archival HARPS, HARPS-N and HIRES data for a total time span of 8 years. This combined dataset significantly improves the masses of the K2-3 planets. We analyse the spectroscopic data with the line-by-line algorithm. We coupled this timeseries with a multi-dimensional Gaussian process framework to disentangle the 40.5-days stellar rotation from the Keplerian signals. We tested models using two activity indicators to ensure the retrieved semi-amplitudes of the planets are not biased by the choice of activity indicator. The multi-dimensional Gaussian process framework, with either activity indicator, yields the following masses: Mb=6.61+/-0.47Me; Mc=2.23+/-0.68Me; Md=2.12+/-1.27Me. Compared to previous works, our detection significance of K2-3b has increased by a factor of two, the mass of K2-3c has slightly decreased and we now have a marginal detection for K2-3d. The positions of the planets in the mass-radius diagram suggest either a H/He-rich or volatile-rich composition for both K2-3b and c, while the nature of K2-3d is ambiguous. A forward atmospheric model suggests that a single visit with JWST can distinguish between a H/He-rich atmosphere from a water-world scenario. This dataset exemplifies the capability of ESPRESSO to detect sub-metre-per-second radial velocity signals for the detection of temperate exoplanets.
Related
- A temperate sub-Neptune transiting the M4 Dwarf TOI-210 identified by NIRPS and TESS -- Uncovering hidden M-dwarf planetary systems in the near-infrared
- Worlds Next Door. V. A Candidate Solar System Scale Super-Jupiter in the 61 Cygni Binary System
- Characterization of the Compact Multi-planet System TOI-789: Validation of Three Terrestrial Planets, Dynamical Characterization, and Detection of a Fourth Temperate Candidate
- Characterization of the Compact Multiplanet System TOI-789: Validation of Three Terrestrial Planets, Dynamical Characterization, and Detection of a Fourth Temperate Candidate
- The γ Cephei System: Updated Orbits, Dynamical Architecture, and Limits on Additional Companions
BibTeX
@misc{srivastava2026uncovering,
title = {{Uncovering temperate worlds: an updated look at the K2-3 system with ESPRESSO}},
author = {Avidaan Srivastava and Emma Pimentel and Amélie Gressier and René Doyon and Melissa J. Hobson and Alessandro Sozzetti and Mario Damasso and Yann Alibert and Susana C. C. Barros and François Bouchy and Amadeo Castro-González and Olivier D. S. Demangeon and Xavier Dumusque and Jonay I. González Hernández and Baptiste Lavie and Jorge Lillo-Box and Christophe Lovis and Giuseppina Micela and Enric Palle and Francesco Pepe and Rafael Rebolo and José Rodrigues and Nuno C. Santos and Sérgio G. Sousa and Alejandro Suárez Mascareño and Stéphane Udry and María R. Zapatero-Osorio},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.17792},
eprint = {2609.17792},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.17792},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Uncovering temperate worlds: an updated look at the K2-3 system with ESPRESSO
AU - Avidaan Srivastava
AU - Emma Pimentel
AU - Amélie Gressier
AU - René Doyon
AU - Melissa J. Hobson
AU - Alessandro Sozzetti
AU - Mario Damasso
AU - Yann Alibert
AU - Susana C. C. Barros
AU - François Bouchy
AU - Amadeo Castro-González
AU - Olivier D. S. Demangeon
AU - Xavier Dumusque
AU - Jonay I. González Hernández
AU - Baptiste Lavie
AU - Jorge Lillo-Box
AU - Christophe Lovis
AU - Giuseppina Micela
AU - Enric Palle
AU - Francesco Pepe
AU - Rafael Rebolo
AU - José Rodrigues
AU - Nuno C. Santos
AU - Sérgio G. Sousa
AU - Alejandro Suárez Mascareño
AU - Stéphane Udry
AU - María R. Zapatero-Osorio
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2609.17792
UR - https://arxiv.org/abs/2609.17792
AB - The K2-3 system is one of the most unique planetary systems as it features three transiting sub-Neptunes in decreasing order of radii, spanning the radius valley. In addition to that, the two outer planets are temperate in nature making this system a perfect laboratory for investigating the nature and formation of small potentially habitable worlds. We present new radial velocity data obtained during the ESPRESSO-GTO programme to add to the archival HARPS, HARPS-N and HIRES data for a total time span of 8 years. This combined dataset significantly improves the masses of the K2-3 planets. We analyse the spectroscopic data with the line-by-line algorithm. We coupled this timeseries with a multi-dimensional Gaussian process framework to disentangle the 40.5-days stellar rotation from the Keplerian signals. We tested models using two activity indicators to ensure the retrieved semi-amplitudes of the planets are not biased by the choice of activity indicator. The multi-dimensional Gaussian process framework, with either activity indicator, yields the following masses: Mb=6.61+/-0.47Me; Mc=2.23+/-0.68Me; Md=2.12+/-1.27Me. Compared to previous works, our detection significance of K2-3b has increased by a factor of two, the mass of K2-3c has slightly decreased and we now have a marginal detection for K2-3d. The positions of the planets in the mass-radius diagram suggest either a H/He-rich or volatile-rich composition for both K2-3b and c, while the nature of K2-3d is ambiguous. A forward atmospheric model suggests that a single visit with JWST can distinguish between a H/He-rich atmosphere from a water-world scenario. This dataset exemplifies the capability of ESPRESSO to detect sub-metre-per-second radial velocity signals for the detection of temperate exoplanets.
ER -