_version_ 1866912754225381376
author Kendall, Alicia
Ulmer-Moll, Solène
Gill, Samuel
Burleigh, Matthew R.
Goad, Michael R.
Anderson, David R.
Bryant, Edward M.
Lavie, Baptiste
Bugatti, Maddalena
Barroso, Javier A. Acevedo
Steiner, Michal
Dragomir, Diana
Villanueva Jr., Steven
Stevens, Daniel J.
Gupta, Arvind F.
Gaudi, Scott
Sun, Guoyou
Claringbold, Alastair
Doyle, Lauren
Guillot, Tristan
Suarez, Olga
Mékarnia, Djamel
Triaud, Amaury H. M. J.
Bendjoya, Philippe
Ziegler, Carl
Mann, Andrew W.
Howell, Steve B.
Fajardo-Acosta, Sergio B.
Littlefield, Colin
Caldwell, Douglas A.
Kunimoto, Michelle
Rowden, Pamela
Kostov, Veselin
Villaseñor, Jesus Noel
Alves, Douglas
Apergis, Ioannis
Armstrong, David J.
Battley, Matthew P.
Bayliss, Daniel
Bouchy, François
Casewell, Sarah L.
Günther, Maximilian N.
Harvey, George T.
Hawthorn, Faith
Jenkins, James S.
Lendl, Monika
McCormac, James
Moyano, Maximilano
Nielsen, Louise D.
Osborn, Ares
Rodel, Toby
Saha, Suman
Udry, Stephane
Vines, Jose I.
Wheatley, Peter J.
Zivave, Tafadzwa
author_facet Kendall, Alicia
Ulmer-Moll, Solène
Gill, Samuel
Burleigh, Matthew R.
Goad, Michael R.
Anderson, David R.
Bryant, Edward M.
Lavie, Baptiste
Bugatti, Maddalena
Barroso, Javier A. Acevedo
Steiner, Michal
Dragomir, Diana
Villanueva Jr., Steven
Stevens, Daniel J.
Gupta, Arvind F.
Gaudi, Scott
Sun, Guoyou
Claringbold, Alastair
Doyle, Lauren
Guillot, Tristan
Suarez, Olga
Mékarnia, Djamel
Triaud, Amaury H. M. J.
Bendjoya, Philippe
Ziegler, Carl
Mann, Andrew W.
Howell, Steve B.
Fajardo-Acosta, Sergio B.
Littlefield, Colin
Caldwell, Douglas A.
Kunimoto, Michelle
Rowden, Pamela
Kostov, Veselin
Villaseñor, Jesus Noel
Alves, Douglas
Apergis, Ioannis
Armstrong, David J.
Battley, Matthew P.
Bayliss, Daniel
Bouchy, François
Casewell, Sarah L.
Günther, Maximilian N.
Harvey, George T.
Hawthorn, Faith
Jenkins, James S.
Lendl, Monika
McCormac, James
Moyano, Maximilano
Nielsen, Louise D.
Osborn, Ares
Rodel, Toby
Saha, Suman
Udry, Stephane
Vines, Jose I.
Wheatley, Peter J.
Zivave, Tafadzwa
contents Beyond orbital periods of 10 days, there is a dearth of known transiting gas giants. On longer orbits, planets are less affected by their host star, and become ideal probes of planet formation, migration and evolution. We report the discovery of a long period Neptune and two Saturns, each initially identified as single transits in the TESS photometry, and solved through additional transits from ground-based follow-up photometric observations by NGTS and ASTEP. High-resolution radial velocity mass measurements using CORALIE and HARPS confirm their planetary nature. From joint modelling of the photometric and spectroscopic data, we determine an orbital period of $43.12655_{-0.00017}^{+0.00012}~$days, radius of $3.65\pm0.22~\mathrm{R_{\oplus}}$, and mass of $19.1_{-4.5}^{+4.9}~\mathrm{M_{\oplus}}$ for NGTS-34b, making it one of the longest period well-characterized transiting Neptunes. Orbiting a late F-type star, bright in the K-band (Kmag$~\simeq7.9$), it is amenable for cool atmosphere studies using JWST or Ariel. TOI-4940b is a small Saturn on a $25.867811_{-0.000056}^{+0.000058}~$day orbit with a radius of $6.61\pm0.37~\mathrm{R_{\oplus}}$ and an upper mass limit $<89~\mathrm{M_{\oplus}}$. NGTS-35b(=TOI-6669b) is a larger Saturn on a $25.241192\pm0.000022~$day, moderately eccentric orbit ($e = 0.192_{-0.033}^{+0.037}$), with a radius of $10.90\pm0.65~\mathrm{R_{\oplus}}$ and a mass of $152_{-19}^{+22}~\mathrm{M_{\oplus}}$. With an assumed albedo $A=0.3$, each of these planets has an equilibrium temperature below 700K, with NGTS-35b especially cold at $450~$K. These three giants add to the small but growing population of long period planets that can further our understanding of planet formation mechanisms.
format Preprint
id arxiv_https___arxiv_org_abs_2512_07716
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle A 43 day transiting Neptune and two 25 day Saturns from TESS, NGTS and ASTEP
Kendall, Alicia
Ulmer-Moll, Solène
Gill, Samuel
Burleigh, Matthew R.
Goad, Michael R.
Anderson, David R.
Bryant, Edward M.
Lavie, Baptiste
Bugatti, Maddalena
Barroso, Javier A. Acevedo
Steiner, Michal
Dragomir, Diana
Villanueva Jr., Steven
Stevens, Daniel J.
Gupta, Arvind F.
Gaudi, Scott
Sun, Guoyou
Claringbold, Alastair
Doyle, Lauren
Guillot, Tristan
Suarez, Olga
Mékarnia, Djamel
Triaud, Amaury H. M. J.
Bendjoya, Philippe
Ziegler, Carl
Mann, Andrew W.
Howell, Steve B.
Fajardo-Acosta, Sergio B.
Littlefield, Colin
Caldwell, Douglas A.
Kunimoto, Michelle
Rowden, Pamela
Kostov, Veselin
Villaseñor, Jesus Noel
Alves, Douglas
Apergis, Ioannis
Armstrong, David J.
Battley, Matthew P.
Bayliss, Daniel
Bouchy, François
Casewell, Sarah L.
Günther, Maximilian N.
Harvey, George T.
Hawthorn, Faith
Jenkins, James S.
Lendl, Monika
McCormac, James
Moyano, Maximilano
Nielsen, Louise D.
Osborn, Ares
Rodel, Toby
Saha, Suman
Udry, Stephane
Vines, Jose I.
Wheatley, Peter J.
Zivave, Tafadzwa
Earth and Planetary Astrophysics
Beyond orbital periods of 10 days, there is a dearth of known transiting gas giants. On longer orbits, planets are less affected by their host star, and become ideal probes of planet formation, migration and evolution. We report the discovery of a long period Neptune and two Saturns, each initially identified as single transits in the TESS photometry, and solved through additional transits from ground-based follow-up photometric observations by NGTS and ASTEP. High-resolution radial velocity mass measurements using CORALIE and HARPS confirm their planetary nature. From joint modelling of the photometric and spectroscopic data, we determine an orbital period of $43.12655_{-0.00017}^{+0.00012}~$days, radius of $3.65\pm0.22~\mathrm{R_{\oplus}}$, and mass of $19.1_{-4.5}^{+4.9}~\mathrm{M_{\oplus}}$ for NGTS-34b, making it one of the longest period well-characterized transiting Neptunes. Orbiting a late F-type star, bright in the K-band (Kmag$~\simeq7.9$), it is amenable for cool atmosphere studies using JWST or Ariel. TOI-4940b is a small Saturn on a $25.867811_{-0.000056}^{+0.000058}~$day orbit with a radius of $6.61\pm0.37~\mathrm{R_{\oplus}}$ and an upper mass limit $<89~\mathrm{M_{\oplus}}$. NGTS-35b(=TOI-6669b) is a larger Saturn on a $25.241192\pm0.000022~$day, moderately eccentric orbit ($e = 0.192_{-0.033}^{+0.037}$), with a radius of $10.90\pm0.65~\mathrm{R_{\oplus}}$ and a mass of $152_{-19}^{+22}~\mathrm{M_{\oplus}}$. With an assumed albedo $A=0.3$, each of these planets has an equilibrium temperature below 700K, with NGTS-35b especially cold at $450~$K. These three giants add to the small but growing population of long period planets that can further our understanding of planet formation mechanisms.
title A 43 day transiting Neptune and two 25 day Saturns from TESS, NGTS and ASTEP
topic Earth and Planetary Astrophysics
url https://arxiv.org/abs/2512.07716