Exoplanet orbital eccentricities derived from LAMOST-Kepler analysis.
The nearly circular (mean eccentricity [Formula: see text]) and coplanar (mean mutual inclination [Formula: see text]) orbits of the solar system planets motivated Kant and Laplace to hypothesize that planets are formed in disks, which has developed into the widely accepted theory of planet formation. The first several hundred extrasolar planets (mostly Jovian) discovered using the radial velocity (RV) technique are commonly on eccentric orbits ([Formula: see text]). This raises a fundamental question: Are the solar system and its formation special? The Kepler mission has found thousands of transiting planets dominated by sub-Neptunes, but most of their orbital eccentricities remain unknown. By using the precise spectroscopic host star parameters from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) observations, we measure the eccentricity distributions for a large (698) and homogeneous Kepler planet sample with transit duration statistics. Nearly half of the planets are in systems with single transiting planets (singles), whereas the other half are multiple transiting planets (multiples). We find an eccentricity dichotomy: on average, Kepler singles are on eccentric orbits with [Formula: see text] 0.3, whereas the multiples are on nearly circular [Formula: see text] and coplanar [Formula: see text] degree) orbits similar to those of the solar system planets. Our results are consistent with previous studies of smaller samples and individual systems. We also show that Kepler multiples and solar system objects follow a common relation [[Formula: see text](1-2)[Formula: see text]] between mean eccentricities and mutual inclinations. The prevalence of circular orbits and the common relation may imply that the solar system is not so atypical in the galaxy after all.
School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China; Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093, China; jwxie@nju.edu.cn dongsubo@pku.edu.cn.
Ji-Wei
JW
Xie
Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China; jwxie@nju.edu.cn dongsubo@pku.edu.cn.
Subo
S
Dong
Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544; Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154.
Zhaohuan
Z
Zhu
Sydney Institute for Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006, Australia; Search for Extraterrestrial Intelligence (SETI) Institute, Mountain View, CA 94043; Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark.
Daniel
D
Huber
Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112.
Zheng
Z
Zheng
Royal Observatory of Belgium, B-1180 Brussels, Belgium.
Peter
P
De Cat
Department of Astronomy, Beijing Normal University, Beijing 100875, China.
Jianning
J
Fu
School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China; Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093, China.
Hui-Gen
HG
Liu
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China.
Ali
A
Luo
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China.
Yue
Y
Wu
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China.
Haotong
H
Zhang
School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China; Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093, China.
Hui
H
Zhang
School of Astronomy and Space Science, Nanjing University, Nanjing 210093, China; Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093, China.
Ji-Lin
JL
Zhou
Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China.
Zihuang
Z
Cao
Nanjing Institute of Astronomical Optics & Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042, China.
Yonghui
Y
Hou
Nanjing Institute of Astronomical Optics & Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042, China.
Yuefei
Y
Wang
Nanjing Institute of Astronomical Optics & Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042, China.
Yong
Y
Zhang
exoplanets; orbital eccentricities; planetary dynamics; solar system; transit
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