Revised planet brightness temperatures using the Planck/LFI 2018 data release.

We present new estimates of the brightness temperatures of Jupiter, Saturn, Uranus, and Neptune, based on the measurements carried in 2009-2013 by Planck/LFI at 30, 44, and 70 GHz and released to the public in 2018. This work extends the results presented in the 2013 and 2015 \Planck/LFI Calibration Papers, based on the data acquired in 2009--2011. Planck observed each planet up to eight times during the nominal mission. We processed time-ordered data from the 22 LFI radiometers to derive planet antenna temperatures for each planet and transit. We accounted for the beam shape and radiometer bandpasses, as well as several systematic effects. We compared our results with WMAP's 9th-year results, Planck/HFI observations, and existing data and models for planetary microwave emissivity. For Jupiter, we obtained Tb = 144.9, 159.8, 170.5 K (pm 0.2 K at 1 sigma, with temperatures expressed using the Rayleigh-Jeans scale) respectively at 30, 44 and 70 GHz, or equivalently a band averaged Planck temperature TbBA=144.7, 160.3, 171.2 K in good agreement with WMAP and existing models. A slight excess at 30 GHz with respect to models is interpreted as an effect of synchrotron emission. Our measures for Saturn agree with WMAP having for rings Tb = 9.2 pm 1.4, 12.6 pm 2.3, 16.2 pm 0.8 K, while for disk we obtained Tb = 140.0 pm 1.4, 147.2 pm 1.2, 150.2 pm 0.4 K, or equivalently a TbBA=139.7, 147.8, 151.0 K. Measures for Uranus (Tb = 152 pm 6, 145 pm 3, 132 pm 2 K, or TbBA=152, 145, 133 K) and Neptune Tb = 154 pm 11, 148 pm 9, 128 pm 3 K, or TbBA=154, 149, 128 K are well in agreement with WMAP and previous data in literature.