TOI-1438: A rare system with two short-period sub-Neptunes and a tentative long-period Jupiter-like planet orbiting a K0V star
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| Format: | Preprint |
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2025
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| author | Persson, Carina M. Knudstrup, Emil Carleo, Ilaria Acuña-Aguirre, Lorena Nowak, Grzegorz Muresan, Alexandra Jankowski, Dawid Gozdziewski, Krzysztof García, Rafael A. Mathur, Savita Palakkatharappil, Dinil B. Borg, Lina Mustill, Alexander J. Barrena, Rafael Fridlund, Malcolm Gandolfi, Davide Hatzes, Artie P. Korth, Judith Luque, Rafael Martín, Eduardo L. Masseron, Thomas Morello, Giuseppe Murgas, Felipe Orell-Miquel, Jaume Palle, Enric Albrecht, Simon H. Bieryla, Allyson Cochran, William D. Crossfield, Ian J. M. Deeg, Hans J. Furlan, Elise Guenther, Eike W. Howell, Steve B. Isaacson, Howard Lam, Kristine W. F. Livingston, John Matson, Rachel A. Matthews, Elisabeth C. Redfield, Seth Schlieder, Joshua E. Seager, Sara Smith, Alexis M. S. Stassun, Keivan G. Twicken, Joseph D. Van Eylen, Vincent Watkins, Cristilyn N. Weiss, Lauren M. |
| author_facet | Persson, Carina M. Knudstrup, Emil Carleo, Ilaria Acuña-Aguirre, Lorena Nowak, Grzegorz Muresan, Alexandra Jankowski, Dawid Gozdziewski, Krzysztof García, Rafael A. Mathur, Savita Palakkatharappil, Dinil B. Borg, Lina Mustill, Alexander J. Barrena, Rafael Fridlund, Malcolm Gandolfi, Davide Hatzes, Artie P. Korth, Judith Luque, Rafael Martín, Eduardo L. Masseron, Thomas Morello, Giuseppe Murgas, Felipe Orell-Miquel, Jaume Palle, Enric Albrecht, Simon H. Bieryla, Allyson Cochran, William D. Crossfield, Ian J. M. Deeg, Hans J. Furlan, Elise Guenther, Eike W. Howell, Steve B. Isaacson, Howard Lam, Kristine W. F. Livingston, John Matson, Rachel A. Matthews, Elisabeth C. Redfield, Seth Schlieder, Joshua E. Seager, Sara Smith, Alexis M. S. Stassun, Keivan G. Twicken, Joseph D. Van Eylen, Vincent Watkins, Cristilyn N. Weiss, Lauren M. |
| contents | We present the detection and characterisation of the TOI-1438 multi-planet system discovered by TESS. We collected a series of follow-up observations including high-spectral resolution observations with HARPS-N over a period of five years. Our modelling shows that the K0V star hosts two transiting sub-Neptunes with Rb = 3.04 +/- 0.19 RE, Rc = 2.75 +/- 0.14 RE, Mb = 9.4 +/- 1.8 ME, and Mc = 10.6 +/- 2.1 ME. The orbital periods of planets b and c are 5.1 and 9.4 days, respectively, corresponding to instellations of 145 +/- 10 and 65 +/- 4 FE. The bulk densities are 1.8 +/- 0.5 and 2.9 +/- 0.7 g cm-3, respectively, suggesting a volatile-rich interior composition. We computed a set of planet interior structure models. Planet b presents a high-metallicity envelope that can accommodate up to 2.5 % in H/He in mass, while planet c cannot have more than 0.2 % as H/He in mass. For any composition of the core considered (Fe-rock or ice-rock), both planets would require a volatile-rich envelope. In addition to the two planets, the radial velocity (RV) data clearly reveal a third signal, likely coming from a non-transiting planet, with an orbital period of 7.6 +1.6 -2.4 years and a radial velocity semi-amplitude of 35+3-5 m s-1. Our best fit model finds a minimum mass of 2.1 +/- 0.3 MJ and an eccentricity of 0.25+0.08-0.11. However, several RV activity indicators also show strong signals at similar periods, suggesting this signal might (partly) originate from stellar activity. More data over a longer period of time are needed to conclusively determine the nature of this signal. If it is confirmed as a triple-planet system, TOI-1438 would be one of the few detected systems to date characterised by an architecture with two small, short-period planets and one massive, long-period planet, where the inner and outer systems are separated by an orbital period ratio of the order of a few hundred. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_21533 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | TOI-1438: A rare system with two short-period sub-Neptunes and a tentative long-period Jupiter-like planet orbiting a K0V star Persson, Carina M. Knudstrup, Emil Carleo, Ilaria Acuña-Aguirre, Lorena Nowak, Grzegorz Muresan, Alexandra Jankowski, Dawid Gozdziewski, Krzysztof García, Rafael A. Mathur, Savita Palakkatharappil, Dinil B. Borg, Lina Mustill, Alexander J. Barrena, Rafael Fridlund, Malcolm Gandolfi, Davide Hatzes, Artie P. Korth, Judith Luque, Rafael Martín, Eduardo L. Masseron, Thomas Morello, Giuseppe Murgas, Felipe Orell-Miquel, Jaume Palle, Enric Albrecht, Simon H. Bieryla, Allyson Cochran, William D. Crossfield, Ian J. M. Deeg, Hans J. Furlan, Elise Guenther, Eike W. Howell, Steve B. Isaacson, Howard Lam, Kristine W. F. Livingston, John Matson, Rachel A. Matthews, Elisabeth C. Redfield, Seth Schlieder, Joshua E. Seager, Sara Smith, Alexis M. S. Stassun, Keivan G. Twicken, Joseph D. Van Eylen, Vincent Watkins, Cristilyn N. Weiss, Lauren M. Earth and Planetary Astrophysics We present the detection and characterisation of the TOI-1438 multi-planet system discovered by TESS. We collected a series of follow-up observations including high-spectral resolution observations with HARPS-N over a period of five years. Our modelling shows that the K0V star hosts two transiting sub-Neptunes with Rb = 3.04 +/- 0.19 RE, Rc = 2.75 +/- 0.14 RE, Mb = 9.4 +/- 1.8 ME, and Mc = 10.6 +/- 2.1 ME. The orbital periods of planets b and c are 5.1 and 9.4 days, respectively, corresponding to instellations of 145 +/- 10 and 65 +/- 4 FE. The bulk densities are 1.8 +/- 0.5 and 2.9 +/- 0.7 g cm-3, respectively, suggesting a volatile-rich interior composition. We computed a set of planet interior structure models. Planet b presents a high-metallicity envelope that can accommodate up to 2.5 % in H/He in mass, while planet c cannot have more than 0.2 % as H/He in mass. For any composition of the core considered (Fe-rock or ice-rock), both planets would require a volatile-rich envelope. In addition to the two planets, the radial velocity (RV) data clearly reveal a third signal, likely coming from a non-transiting planet, with an orbital period of 7.6 +1.6 -2.4 years and a radial velocity semi-amplitude of 35+3-5 m s-1. Our best fit model finds a minimum mass of 2.1 +/- 0.3 MJ and an eccentricity of 0.25+0.08-0.11. However, several RV activity indicators also show strong signals at similar periods, suggesting this signal might (partly) originate from stellar activity. More data over a longer period of time are needed to conclusively determine the nature of this signal. If it is confirmed as a triple-planet system, TOI-1438 would be one of the few detected systems to date characterised by an architecture with two small, short-period planets and one massive, long-period planet, where the inner and outer systems are separated by an orbital period ratio of the order of a few hundred. |
| title | TOI-1438: A rare system with two short-period sub-Neptunes and a tentative long-period Jupiter-like planet orbiting a K0V star |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2508.21533 |