M Dwarf Singles and Multis Have Dissimilar Metallicities Indicating Different Origins
Abstract
It is unclear if host star metallicities differ between systems with one detected transiting planet ("singles") or multiple detected transiting planets ("multis") around FGK dwarfs. Here, we find strong evidence that they do for M dwarfs. We use a homogeneous sample of FGK and M dwarf chemical abundances to demonstrate that M dwarf multis are significantly more metal-poor than singles (p = 0.00079), even when we only consider small (<4 R⊕) planets (p = 0.0013). This result emerges at the late-K to M dwarf transition. We observe that M dwarf multis become more metal-poor as a function of increasing planet multiplicity. Additionally, planets in singles have significantly higher eccentricities and shorter orbital periods compared to planets in multis. We interpret these findings as evidence that M dwarf singles lead relatively active dynamical lives, and the different planetary architectures of singles and multis arise from distinct dynamics influenced by metallicity. This may not occur in FGK systems because their more massive protoplanetary disks may supply enough planet-forming material to instigate dynamics that lead to only one transiting planet, even when the host star metallicity is low. Another possibility is that multis are less compact around FGK dwarfs because they form from larger disks, which may often cause them to be observed as singles in transit data.
Related
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BibTeX
@misc{behmard2026dwarf,
title = {{M Dwarf Singles and Multis Have Dissimilar Metallicities Indicating Different Origins}},
author = {Aida Behmard and Sheila Sagear and Yuxi and Lu and Romy Rodríguez Martínez and Adrian M. Price-Whelan and Soichiro Hattori},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.27013},
eprint = {2609.27013},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.27013},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - M Dwarf Singles and Multis Have Dissimilar Metallicities Indicating Different Origins
AU - Aida Behmard
AU - Sheila Sagear
AU - Yuxi
AU - Lu
AU - Romy Rodríguez Martínez
AU - Adrian M. Price-Whelan
AU - Soichiro Hattori
PY - 2026
DA - 2026/09/22
PB - arXiv
DO - 10.48550/arxiv.2609.27013
UR - https://arxiv.org/abs/2609.27013
AB - It is unclear if host star metallicities differ between systems with one detected transiting planet ("singles") or multiple detected transiting planets ("multis") around FGK dwarfs. Here, we find strong evidence that they do for M dwarfs. We use a homogeneous sample of FGK and M dwarf chemical abundances to demonstrate that M dwarf multis are significantly more metal-poor than singles (p = 0.00079), even when we only consider small (<4 R_⊕) planets (p = 0.0013). This result emerges at the late-K to M dwarf transition. We observe that M dwarf multis become more metal-poor as a function of increasing planet multiplicity. Additionally, planets in singles have significantly higher eccentricities and shorter orbital periods compared to planets in multis. We interpret these findings as evidence that M dwarf singles lead relatively active dynamical lives, and the different planetary architectures of singles and multis arise from distinct dynamics influenced by metallicity. This may not occur in FGK systems because their more massive protoplanetary disks may supply enough planet-forming material to instigate dynamics that lead to only one transiting planet, even when the host star metallicity is low. Another possibility is that multis are less compact around FGK dwarfs because they form from larger disks, which may often cause them to be observed as singles in transit data.
ER -