M. Hon, D. Huber, N. Z. Rui, J. Fuller, D. Veras, J. S. Kuszlewicz, O. Kochukhov, A. Stokholm, J. L. Rørsted, M. Yildiz, Z. Çelik Orhan, S. Örtel, C. Jiang, D. R. Hey, H. Isaacson, J. Zhang, M. Vrard, K. G. Stassun, B. J. Shappee, J. Tayar, Z. R. Claytor, C. Beard, T. R. Bedding, C. L. Brinkman, T. L. Campante, W. J. Chaplin, A. Chontos, S. Giacalone, R. Holcomb, A. W. Howard, J. Lubin, M. MacDougall, B. T. Montet, Joseph M. A. Murphy, J. M. J. Ong, D. Pidhorodetska, A. S. Polanski, M. Rice, D. Stello, D. Tyler, J. Van Zandt, L. M. Weiss
Abstract
When main-sequence stars expand into red giants, they are expected to engulf close-in planets. Until now, the absence of planets with short orbital periods around post-expansion, core-helium-burning red giants has been interpreted as evidence that short-period planets around Sun-like stars do not survive the giant expansion phase of their host stars. Here we present the discovery that the giant planet 8 Ursae Minoris b orbits a core-helium-burning red giant. At a distance of only 0.5 AU from its host star, the planet would have been engulfed by its host star, which is predicted by standard single-star evolution to have previously expanded to a radius of 0.7 AU. Given the brief lifetime of helium-burning giants, the nearly circular orbit of the planet is challenging to reconcile with scenarios in which the planet survives by having a distant orbit initially. Instead, the planet may have avoided engulfment through a stellar merger that either altered the evolution of the host star or produced 8 Ursae Minoris b as a second-generation planet. This system shows that core-helium-burning red giants can harbour close planets and provides evidence for the role of non-canonical stellar evolution in the extended survival of late-stage exoplanetary systems.
Keywords
Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Earth and Planetary Astrophysics
Nature
Volume 618, Number 7667, Page 917
2023 June
