An Outer Giant Excites and Constrains the Orbit of π Mensae d
Abstract
The nearby π Mensae system contains the eccentric giant planet b on a 5.7 yr orbit, the 6.27 day transiting sub-Neptune c, and a candidate planet d on a 123 day orbit between them. Published estimates place the eccentricity of d between approximately 0.2 and 0.4. We reanalyze 772 published velocities with three-Keplerian fits and explore three-dimensional b-d dynamics with N-body integrations. The high-eccentricity solution persists when the phase or apsidal prior is widened; exact importance reweighting to a population-informed Beta eccentricity prior gives ed=0.378+0.050−0.049. In 20 kyr integrations, 84.5% of configurations near the prograde and retrograde coplanar endpoints survive, compared with 21.3% across 60∘ ≤ Ibd < 120∘; stellar collisions dominate the failures. Secular forcing by b moves 53 of 62 one-Myr survivors initialized with ed ≤ 0.1 into 0.3 ≤ ed ≤ 0.5. Representative b+d configurations remain viable for 100 Myr, whereas controls with c and general relativity retain fewer systems. The outer giant can therefore excite the observed eccentricity of d while constraining its viable orbit toward prograde or retrograde near-coplanar configurations.
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BibTeX
@misc{jiang2026outer,
title = {{An Outer Giant Excites and Constrains the Orbit of $π$ Mensae d}},
author = {Qunfeng Jiang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.06682},
eprint = {2609.06682},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.06682},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - An Outer Giant Excites and Constrains the Orbit of π Mensae d
AU - Qunfeng Jiang
PY - 2026
DA - 2026/09/06
PB - arXiv
DO - 10.48550/arxiv.2609.06682
UR - https://arxiv.org/abs/2609.06682
AB - The nearby π Mensae system contains the eccentric giant planet b on a 5.7 yr orbit, the 6.27 day transiting sub-Neptune c, and a candidate planet d on a 123 day orbit between them. Published estimates place the eccentricity of d between approximately 0.2 and 0.4. We reanalyze 772 published velocities with three-Keplerian fits and explore three-dimensional b-d dynamics with N-body integrations. The high-eccentricity solution persists when the phase or apsidal prior is widened; exact importance reweighting to a population-informed Beta eccentricity prior gives e_d=0.378^+0.050_−0.049. In 20 kyr integrations, 84.5% of configurations near the prograde and retrograde coplanar endpoints survive, compared with 21.3% across 60^∘ ≤ I_bd < 120^∘; stellar collisions dominate the failures. Secular forcing by b moves 53 of 62 one-Myr survivors initialized with e_d ≤ 0.1 into 0.3 ≤ e_d ≤ 0.5. Representative b+d configurations remain viable for 100 Myr, whereas controls with c and general relativity retain fewer systems. The outer giant can therefore excite the observed eccentricity of d while constraining its viable orbit toward prograde or retrograde near-coplanar configurations.
ER -