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Ultra-short period (USP) planets are a class of exoplanets with periodsshorter than one day. The origin of this sub-population of planets is stillunclear, with different formation scenarios highly dependent on the compositionof the USP planets. A better understanding of this class of exoplanets will,therefore, require an increase in the sample of such planets that have accurateand precise masses and radii, which also includes estimates of the level ofirradiation and information about possible companions. Here we report adetailed characterization of a USP planet around the solar-type star HD 80653$\equiv$ EP 251279430 using the K2 light curve and 108 precise radialvelocities obtained with the HARPS-N spectrograph, installed on the TelescopioNazionale Galileo. From the K2 C16 data, we found one super-Earth planet($R_{b}=1.613\pm0.071 R_{\oplus}$) transiting the star on a short-period orbit($P_{\rm b}=0.719573\pm0.000021$ d). From our radial velocity measurements, weconstrained the mass of HD 80653 b to $M_{b}=5.60\pm0.43 M_{\oplus}$. We alsodetected a clear long-term trend in the radial velocity data. We derived thefundamental stellar parameters and determined a radius of$R_{\star}=1.22\pm0.01 R_{\odot}$ and mass of $M_{\star}=1.18\pm0.04M_{\odot}$, suggesting that HD 80653, has an age of $2.7\pm1.2$ Gyr. The bulkdensity ($\rho_{b} = 7.4 \pm 1.1$ g cm$^{-3}$) of the planet is consistent withan Earth-like composition of rock and iron with no thick atmosphere. Ouranalysis of the K2 photometry also suggests hints of a shallow secondaryeclipse with a depth of 8.1$\pm$3.7 ppm. Flux variations along the orbitalphase are consistent with zero. The most important contribution might come fromthe day-side thermal emission from the surface of the planet at $T\sim3480$ K.

An ultra-short period rocky super-Earth orbiting the G2-star HD 80653