**Authors**. Sara Gettel, David Charbonneau, Courtney D. Dressing, Lars A. Buchhave, Xavier Dumusque, Andrew Vanderburg, Aldo S. Bonomo, Luca Malavolta, Francesco Pepe, Andrew Collier Cameron, David W. Latham, Stephane Udry, Geoffrey W. Marcy, Howard Isaacson, Andrew W. Howard, Guy R. Davies, Victor Silva Aguirre, Hans Kjeldsen, Timothy R. Bedding, Eric Lopez, Laura Affer, Rosario Cosentino, Pedro Figueira, Aldo F. M. Fiorenzano, Avet Harutyunyan, John Asher Johnson, Mercedes Lopez-Morales, Christophe Lovis, Michel Mayor, Giusi Micela, Emilio Molinari, Fatemeh Motalebi, David F. Phillips, Giampaolo Piotto, Didier Queloz, Ken Rice, Dimitar Sasselov, Damien Segransan, Alessandro Sozzetti, Chris Watson, Sarbani Basu, Tiago L. Campante, Jorgen Christensen-Dalsgaard, Steven D. Kawaler, Travis S. Metcalfe, Rasmus Handberg, Mikkel N. Lund, Mia S. Lundkvist, Daniel Huber, William J. Chaplin

**Journal**. The Astrophysical Journal

**Abstract. **Kepler-454 (KOI-273) is a relatively bright (V = 11.69 mag), Sun-like star that hosts a transiting planet candidate in a 10.6 day orbit. From spectroscopy, we estimate the stellar temperature to be 5687 ± 50 K, its metallicity to be [m/H] = 0.32 ± 0.08, and the projected rotational velocity to be v sin i 〈 2.4 km s^{-1}. We combine these values with a study of the asteroseismic frequencies from short cadence Kepler data to estimate the stellar mass to be {1.028}_{-0.03}^{+0.04}{M}_{☉ }, the radius to be 1.066 ± 0.012 R_{☉}, and the age to be {5.25}_{-1.39}^{+1.41} Gyr. We estimate the radius of the 10.6 day planet as 2.37 ± 0.13 R_{⊕}. Using 63 radial velocity observations obtained with the HARPS-N spectrograph on the Telescopio Nazionale Galileo and 36 observations made with the HIRES spectrograph at the Keck Observatory, we measure the mass of this planet to be 6.8 ± 1.4 M_{⊕}. We also detect two additional non-transiting companions, a planet with a minimum mass of 4.46 ± 0.12 M_{J} in a nearly circular 524 day orbit and a massive companion with a period 〉10 years and mass 〉12.1 M_{J}. The 12 exoplanets with radii 〈2.7 R_{⊕} and precise mass measurements appear to fall into two populations, with those 〈1.6 R_{⊕} following an Earth-like composition curve and larger planets requiring a significant fraction of volatiles. With a density of 2.76 ± 0.73 g cm^{-3}, Kepler-454b lies near the mass transition between these two populations and requires the presence of volatiles and/or H/He gas.