  The advent of a new generation of radial velocity instruments has allowed us
to break the one Earth-mass barrier. We report a new milestone in this context
with the detection of the lowest-mass planet measured so far using radial
velocities: L 98-59 b, a rocky planet with half the mass of Venus. It is part
of a system composed of three known transiting terrestrial planets (planets b
to d). We announce the discovery of a fourth nontransiting planet with a
minimum mass of 3.06_{-0.37}^{+0.33} MEarth and an orbital period of
12.796_{-0.019}^{+0.020} days and report indications for the presence of a
fifth nontransiting terrestrial planet. With a minimum mass of
2.46_{-0.82}^{+0.66} MEarth and an orbital period 23.15_{-0.17}^{+0.60} days,
this planet, if confirmed, would sit in the middle of the habitable zone of the
L 98-59 system.
  L 98-59 is a bright M dwarf located 10.6 pc away. Positioned at the border of
the continuous viewing zone of the James Webb Space Telescope, this system is
destined to become a corner stone for comparative exoplanetology of terrestrial
planets. The three transiting planets have transmission spectrum metrics
ranging from 49 to 255, which makes them prime targets for an atmospheric
characterization with the James Webb Space Telescope, the Hubble Space
Telescope, Ariel, or ground-based facilities such as NIRPS or ESPRESSO. With an
equilibrium temperature ranging from 416 to 627 K, they offer a unique
opportunity to study the diversity of warm terrestrial planets.
  L 98-59 b and c have densities of 3.6_{-1.5}^{+1.4} and 4.57_{-0.85}^{+0.77}
g.cm^{-3}, respectively, and have very similar bulk compositions with a small
iron core that represents only 12 to 14 % of the total mass, and a small amount
of water. However, with a density of 2.95_{-0.51}^{+0.79} g.cm^{-3} and despite
a similar core mass fraction, up to 30 % of the mass of L 98-59 d might be
water.
