![Radial velocity timeseries of K2-3 used in the analysis. Here the second dimension for the multi-dimensional quasi-periodic gaussian process kernes used the D2V activity indicator to disentangle the stellar activity from the Keplerian signals. The Keplerian models for all three planets are assumed to be circular orbits for this figure (Model 1 in Table C.3). The various instruments used in the analysis are colour coded. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/Uncovering.png?fit=1200%2C679&ssl=1)
[astro-ph.EP] 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.
Avidaan Srivastava, Emma Pimentel, Amélie Gressier, René Doyon, Melissa J. Hobson, Alessandro Sozzetti, Mario Damasso, Yann Alibert, Susana C. C. Barros, François Bouchy, Amadeo Castro-González, Olivier D. S. Demangeon, Xavier Dumusque, Jonay I. González Hernández, Baptiste Lavie, Jorge Lillo-Box, Christophe Lovis, Giuseppina Micela, Enric Palle, Francesco Pepe, Rafael Rebolo, José Rodrigues, Nuno C. Santos, Sérgio G. Sousa, Alejandro Suárez Mascareño, Stéphane Udry, María R. Zapatero-Osorio
Comments: 10 pages, 5 figures, 3 tables. Submitted to A&A Letters. Abstract shortened to fit ArXiv character limitations
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2609.17792 [astro-ph.EP] (or arXiv:2609.17792v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.17792
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Submission history
From: Avidaan Srivastava
[v1] Tue, 15 Sep 2026 19:57:07 UTC (1,192 KB)
https://arxiv.org/abs/2609.17792
Astrobiology,
