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Edge-of-the-Multis: Evidence for a Transition in the Outer Architectures of Compact Multiplanet Systems

Millholland, Sarah C. and He, Matthias Y. and Zink, Jon K. (2022) Edge-of-the-Multis: Evidence for a Transition in the Outer Architectures of Compact Multiplanet Systems. Astronomical Journal, 164 (2). Art. No. 72. ISSN 0004-6256. doi:10.3847/1538-3881/ac7c67.

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Although the architectures of compact multiple-planet systems are well characterized, there has been little examination of their “outer edges,” or the locations of their outermost planets. Here we present evidence that the observed high-multiplicity Kepler systems truncate at smaller orbital periods than can be explained by geometric and detection biases alone. To show this, we considered the existence of hypothetical planets orbiting beyond the observed transiting planets with properties dictated by the “peas-in-a-pod” patterns of intrasystem radius and period ratio uniformity. We evaluated the detectability of these hypothetical planets using (1) a novel approach for estimating the mutual inclination dispersion of multitransiting systems based on transit chord length ratios, and (2) a model of transit probability and detection efficiency that accounts for the impacts of planet multiplicity on completeness. Under the assumption that the “peas-in-a-pod” patterns continue to larger orbital separations than observed, we find that ≳35% of Kepler compact multis should possess additional detected planets beyond the known planets, constituting a ∼7σ discrepancy with the lack of such detections. These results indicate that the outer (∼100–300 days) regions of compact multis experience a truncation (i.e., an “edge-of-the-multis”) or a significant breakdown of the “peas-in-a-pod” patterns, in the form of systematically smaller radii or larger period ratios. We outline future observations that can distinguish these possibilities, and we discuss implications for planet formation theories.

Item Type:Article
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URLURL TypeDescription Paper
Millholland, Sarah C.0000-0003-3130-2282
He, Matthias Y.0000-0002-5223-7945
Zink, Jon K.0000-0003-1848-2063
Alternate Title:Edge-of-the-Multis: Evidence for a Transition in the Outer Architectures of Compact Multi-Planet Systems
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 April 20; revised 2022 June 21; accepted 2022 June 26; published 2022 August 1. We thank the anonymous referee for their careful review and constructive comments. We are grateful to Fred Adams, Chris Burke, Eric Ford, Dan Tamayo, Jonathan Tan, and Josh Winn for helpful discussions. S.C.M. was supported by NASA through a NASA Hubble Fellowship grant #HST-HF2-51465 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51465
Subject Keywords:Exoplanets; Super Earths; Mini Neptunes; Exoplanet systems; Exoplanet dynamics; Exoplanet formation
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Exoplanets (498); Super Earths (1655); Mini Neptunes (1063); Exoplanet systems (484); Exoplanet dynamics (490); Exoplanet formation (492)
Record Number:CaltechAUTHORS:20220811-235050000
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Official Citation:Sarah C. Millholland et al 2022 AJ 164 72
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116257
Deposited By: George Porter
Deposited On:12 Aug 2022 02:15
Last Modified:12 Aug 2022 02:15

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