Five Planets Orbiting 55 Cancri

Abstract

We report 18 years of Doppler shift measurements of a nearby star, 55 Cancri, that exhibit strong evidence for five orbiting planets. The four previously reported planets are strongly confirmed here. A fifth planet is presented, with an apparent orbital period of 260 days, placing it 0.78 AU from the star in the large empty zone between two other planets. The velocity wobble amplitude of 4.9 \ms implies a minimum planet mass \msini = 45.7 \mearthe. The orbital eccentricity is consistent with a circular orbit, but modest eccentricity solutions give similar \chisq fits. All five planets reside in low eccentricity orbits, four having eccentricities under 0.1. The outermost planet orbits 5.8 AU from the star and has a minimum mass, \msini = 3.8 \mjupe, making it more massive than the inner four planets combined. Its orbital distance is the largest for an exoplanet with a well defined orbit. The innermost planet has a semi-major axis of only 0.038 AU and has a minimum mass, \msinie, of only 10.8 \mearthe, one of the lowest mass exoplanets known. The five known planets within 6 AU define a {\em minimum mass protoplanetary nebula} to compare with the classical minimum mass solar nebula. Numerical N-body simulations show this system of five planets to be dynamically stable and show that the planets with periods of 14.65 and 44.3 d are not in a mean-motion resonance. Millimagnitude photometry during 11 years reveals no brightness variations at any of the radial velocity periods, providing support for their interpretation as planetary.Comment: accepted to Ap

Variability in the super-Earth 55 Cnc e

“…55 Cnc has been found to be a quiescent star showing on rare occasions variability at the 6 millimagnitude level, corresponding to a <1% coverage in star spots (Fischer et al 2008). When detected, this variability has a periodicity of about 40 days, corresponding to the rotational period of the star.…”

HD 5388 b is a 69 MJupcompanion instead of a planet

“…-55 Cnc has five planetary companions announced by Fischer et al (2008). The planet 55 Cnc d has a minimum mass of M 2 sin i = 3.84 M J .…”

K2-66b and K2-106b: Two Extremely Hot Sub-Neptune-size Planets with High Densities

“…Only five other USPs have measured masses and densities: 55 Cnc (Fischer et al 2008;Dawson & Fabrycky 2010;Nelson et al 2014;Demory et al 2016), CoRoT-7b (Léger et al 2009;Bruntt et al 2010;Haywood et al 2014), Kepler-10b Esteves et al 2015), Kepler-78b (Howard et al 2013;Pepe et al 2013;Grunblatt et al 2015), and WASP-47e Dai et al 2015;Sinukoff et al 2017). These planets are plotted on the mass-radius diagram in Figure 7(b).…”