Unraveling the brown dwarf desert: Four new discoveries and a unifying period-coded picture

¹ Astronomical Institute, Czech Academy of Sciences, Fričova 298, 251 65, Ondřejov, Czech Republic
² Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
³ Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Av. Diagonal las Torres 2640, Peñalolén, Santiago, Chile
⁴ Millennium Institute for Astrophysics, Nuncio Monseñor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile
⁵ Astronomical Institute of Charles University, V Holešovičkách 2, 180 00 Prague, Czech Republic
⁶ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁷ Department of Astronomy, The Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210, USA
⁸ School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
⁹ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 70 Vassar St., Cambridge, MA 02139, USA
¹⁰ Department of Astronomy, Sofia University “St Kliment Ohridski”, 5 James Bourchier Blvd, 1164 Sofia, Bulgaria
¹¹ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹² Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
¹³ Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic
¹⁴ El Sauce Observatory – Obstech, Coquimbo, Chile
¹⁵ Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
¹⁶ Department of Electrical Engineering and Center of Astro Engineering, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
¹⁷ Silesian University of Technology, Akademicka 16, 44-100 Gliwice, Poland
¹⁸ Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile
¹⁹ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
²⁰ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
²¹ Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA
²² Thueringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²³ Institute of Plasma Physics of the Czech Academy of Sciences, Research Centre for Special Optics and Optoelectronic Systems TOPTEC, U Slovanky 2525/1a, 182 00 Prague, Czech Republic
²⁴ Department of Physics and Astronomy, Union College, 807 Union St., Schenectady, NY 12308, USA
²⁵ Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario M5S 3H4, Canada

^★ Corresponding authors.

Received: 24 November 2025
Accepted: 10 March 2026

Abstract

We present four newly validated transiting brown dwarfs identified through TESS photometry and confirmed with high-precision radial velocity measurements obtained from the FEROS and PLATOSpec spectrographs. Notably, three of these companions exhibit orbital periods exceeding 100 days, thereby expanding the sample of long-period transiting brown dwarfs from four to seven systems. The host stars of the long-period brown dwarfs show mild subsolar metallicity. These discoveries highlight the expansion of the metal-poor long-period distribution and help us better understand the brown dwarf desert. In our comparative analysis of eccentricity and metallicity demographics, we utilized catalogs of long-period giant planets, brown dwarfs, and low-mass stellar companions. After accounting for tidal influences, the eccentricity distribution aligns with that of low-mass stellar binaries, presenting a different profile than that observed within the giant planet population. Additionally, the metallicity of the host stars reveals a noteworthy trend: Short-period transiting brown dwarfs are predominantly associated with metal-rich stars, whereas long-period brown dwarfs are more often found around metal-poor stars, thus demonstrating statistical similarities to low-mass stellar hosts. This trend has been previously observed in studies of hot and cold Jupiters and points to a period-coded mixture of channels. A natural explanation is that most brown dwarfs originate from fragmentation at wider separations, with long-period systems retaining this stellar-like imprint, while only those embedded in massive, long-lived metal-rich protoplanetary disks are efficiently delivered and stabilized to short orbits.