THYME. XIII. Two Young Neptunes Orbiting a 75 Myr Star in the Alpha Persei Cluster
Abstract Young planets with mass measurements are particularly valuable in studying atmospheric mass-loss processes, but these planets are rare and their masses difficult to measure due to stellar activity. We report the discovery of a planetary system around TOI-6109, a young, 75 Myr-old Sun-like star in the Alpha Persei cluster. It hosts at least two transiting Neptune-like planets within 10 day orbital periods. Using three TESS sectors, 30 CHEOPS orbits, and photometric follow-up observations from the ground, we confirm the signals of the two planets. TOI-6109 b has an orbital period of P = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>5.690</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.0004</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.0004</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> days and a radius of R = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>4.8</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.12</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.16</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> R ⊕ . The outer planet, TOI-6109 c has an orbital period of P = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>8.538</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.0005</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.0006</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> days and a radius of R = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>4.8</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> R ⊕ . These planets orbit just outside a 3:2 mean motion resonance. The near-resonant configuration presents the opportunity to measure the planet’s mass via TTV measurements and to bypass difficult RV measurements. Measuring the masses of the planets in this system will allow us to test theoretical models of atmospheric mass loss.
Authors
- Andrew W. Mann (ORCID: https://orcid.org/0000-0003-3654-1602)
- Ronan Kerr (ORCID: https://orcid.org/0000-0002-6549-9792)
- Annelies Mortier (ORCID: https://orcid.org/0000-0001-7254-4363)
- Bob Massey (ORCID: https://orcid.org/0000-0001-8879-7138)
- Nicholas Scarsdale (ORCID: https://orcid.org/0000-0003-3623-7280)
- Juliette Becker (ORCID: https://orcid.org/0000-0002-7733-4522)
- Cristilyn N. Watkins (ORCID: https://orcid.org/0000-0001-8621-6731)
- David W. Latham (ORCID: https://orcid.org/0000-0001-9911-7388)
- Elisabeth Newton (ORCID: https://orcid.org/0000-0003-4150-841X)
- Madyson G. Barber (ORCID: https://orcid.org/0000-0002-8399-472X)
- Karen A. Collins (ORCID: https://orcid.org/0000-0001-6588-9574)
- Chris Stockdale (ORCID: https://orcid.org/0000-0003-2163-1437)
- Steve B. Howell (ORCID: https://orcid.org/0000-0002-2532-2853)
- Emily A. Gilbert (ORCID: https://orcid.org/0000-0002-0388-8004)
- Juliana García‐Mejía (ORCID: https://orcid.org/0000-0003-1361-985X)
- Roberto Zambelli (ORCID: https://orcid.org/0009-0009-0994-1767)
- Richard P. Schwarz (ORCID: https://orcid.org/0000-0001-8227-1020)
- David Charbonneau (ORCID: https://orcid.org/0000-0002-9003-484X)
- Andrew Vanderburg (ORCID: https://orcid.org/0000-0001-7246-5438)
- Anne Dattilo (ORCID: https://orcid.org/0000-0002-1092-2995)
- Thomas Barclay (ORCID: https://orcid.org/0000-0001-7139-2724)
- Alex S. Polanski (ORCID: https://orcid.org/0000-0001-7047-8681)
- Joseph M. Akana Murphy (ORCID: https://orcid.org/0000-0001-8898-8284)
- Francis P. Wilkin (ORCID: https://orcid.org/0000-0003-2127-8952)
- David R. Ciardi (ORCID: https://orcid.org/0000-0002-5741-3047)
- Patrick Tamburo (ORCID: https://orcid.org/0000-0003-2171-5083)
- Joseph R. Livesey (ORCID: https://orcid.org/0000-0003-3888-3753)
- Adam L. Kraus (ORCID: https://orcid.org/0000-0001-9811-568X)
- T. G. Wilson (ORCID: https://orcid.org/0000-0001-8749-1962)
- Allyson Bieryla (ORCID: https://orcid.org/0000-0001-6637-5401)
- Ian J. M. Crossfield
Institutions
- Dartmouth College (US)
- University of North Carolina at Chapel Hill (US)
- Ames Research Center (US)
- Goddard Space Flight Center (US)
- Pennsylvania State University (US)
- Jet Propulsion Laboratory (US)
- University of Wisconsin–Madison (US)
- University of Kansas (US)
- Union College (US)
- University of California, Santa Cruz (US)
- University of Toronto (CA)
- American Association of Variable Star Observers (US)
- Lowell Observatory (US)
- Oakwood Academy (GB)
- NASA Exoplanet Science Institute (US)
- Società Italiana di Fisica (IT)
- University of Warwick (GB)
- Canadian Institute for Theoretical Astrophysics (CA)
- Center for Astrophysics Harvard & Smithsonian (US)
- Massachusetts Institute of Technology (US)
- University of Birmingham (GB)
- The University of Texas at Austin (US)
Publication Details
- Journal
- The Astronomical Journal
- Published
- 2025-11-11
- DOI
- https://doi.org/10.3847/1538-3881/ae0a35
- Primary Topic
- Stellar, planetary, and galactic studies
- Type
- article
- Field-Weighted Citation Impact
- 0.00