  We report the detection of a transiting Earth-size planet around GJ 357, a
nearby M2.5V star, using data from the Transiting Exoplanet Survey Satellite
(TESS). GJ 357 b (TOI-562.01) is a transiting, hot, Earth-sized planet
(Teq=525+-11 K) with a radius of Rb=1.217+-0.084 Re and an orbital period of
Pb=3.93 d. Precise stellar radial velocities from CARMENES and PFS, as well as
archival data from HIRES, UVES, and HARPS also display a 3.93-day periodicity,
confirming the planetary nature and leading to a planetary mass of
Mb=1.84+-0.31 Me. In addition to the radial velocity signal for GJ 357 b, more
periodicities are present in the data indicating the presence of two further
planets in the system: GJ 357 c, with a minimum mass of Mc=3.40+-0.46 Me in a
9.12 d orbit, and GJ 357 d, with a minimum mass of Md=6.1+-1.0 Me in a 55.7 d
orbit inside the habitable zone. The host is relatively inactive and exhibits a
photometric rotation period of Prot=78+-2 d. GJ 357 b is to date the second
closest transiting planet to the Sun, making it a prime target for further
investigations such as transmission spectroscopy. Therefore, GJ 357 b
represents one of the best terrestrial planets suitable for atmospheric
characterization with the upcoming JWST and ground-based ELTs.
