On the patterns observed in Kepler multi-planet systems. (arXiv:1907.02074v3 [astro-ph.EP] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Zhu_W/0/1/0/all/0/1">Wei Zhu</a> (CITA)
Recent studies claimed that planets around the same star have similar sizes
and masses and regular spacings, and that planet pairs usually show ordered
sizes such that the outer planet is usually the larger one. Here I show that
these patterns can be largely explained by detection biases. The emph{Kepler}
planet detections are set by the transit signal-to-noise ratio (S/N). For
different stellar properties and orbital period values, the same S/N
corresponds to different planetary sizes. This variation in the detection
threshold naturally leads to apparent correlations in planet sizes and the
observed size ordering. The apparently correlated spacings, measured in period
ratios, between adjacent planet pairs in systems with at least three detected
planets are partially due to the arbitrary upper limit that the earlier study
imposed on the period ratio, and partially due to the varying stability
threshold for different planets. After these detection biases are taken into
account, we do not find strong evidence for the so-called “intra-system
uniformity” or the size ordering effect. Instead, the physical properties of
emph{Kepler} planets are largely independent of the properties of their
siblings and the parent star. It is likely that the dynamical evolution has
erased the memory of emph{Kepler} planets about their initial formation
conditions. In other words, it will be difficult to infer the initial
conditions from the observed properties and the architecture of emph{Kepler}
planets.
Recent studies claimed that planets around the same star have similar sizes
and masses and regular spacings, and that planet pairs usually show ordered
sizes such that the outer planet is usually the larger one. Here I show that
these patterns can be largely explained by detection biases. The emph{Kepler}
planet detections are set by the transit signal-to-noise ratio (S/N). For
different stellar properties and orbital period values, the same S/N
corresponds to different planetary sizes. This variation in the detection
threshold naturally leads to apparent correlations in planet sizes and the
observed size ordering. The apparently correlated spacings, measured in period
ratios, between adjacent planet pairs in systems with at least three detected
planets are partially due to the arbitrary upper limit that the earlier study
imposed on the period ratio, and partially due to the varying stability
threshold for different planets. After these detection biases are taken into
account, we do not find strong evidence for the so-called “intra-system
uniformity” or the size ordering effect. Instead, the physical properties of
emph{Kepler} planets are largely independent of the properties of their
siblings and the parent star. It is likely that the dynamical evolution has
erased the memory of emph{Kepler} planets about their initial formation
conditions. In other words, it will be difficult to infer the initial
conditions from the observed properties and the architecture of emph{Kepler}
planets.
http://arxiv.org/icons/sfx.gif
