Kepler78 and the UltraShortPeriod planets
Abstract
Compared to the Earth, the exoplanet Kepler78b has a similar size (1.2 R_{⊕}) and an orbital period a thousand times shorter (8.5 h). It is currently the smallest planet for which the mass, radius, and dayside brightness have all been measured. Kepler78b is an exemplar of the ultrashortperiod (USP) planets, a category defined by the simple criterion P_{orb} < 1 day. We describe our Fourierbased search of the Kepler data that led to the discovery of Kepler78b, and review what has since been learned about the population of USP planets. They are about as common as hot Jupiters, and they are almost always smaller than 2 R_{⊕}. They are often members of compact multiplanet systems, although they tend to have relatively large period ratios and mutual inclinations. They might be the exposed rocky cores of "gas dwarfs," the planets between 24 R_{⊕} in size that are commonly found in somewhat wider orbits.
 Publication:

New Astronomy Reviews
 Pub Date:
 November 2018
 DOI:
 10.1016/j.newar.2019.03.006
 arXiv:
 arXiv:1803.03303
 Bibcode:
 2018NewAR..83...37W
 Keywords:

 Planets;
 Timeseries photometry;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 fixed error in Eq. (4)