  We present precision radial velocity (RV) data that reveal a multiple
exoplanet system orbiting the bright nearby G5V star 61 Virginis. Our 4.6 years
of combined Keck/HIRES and Anglo-Australian Telescope precision RVs indicate
the hitherto unknown presence of at least three planets orbiting this
well-studied star. These planets are all on low-eccentricity orbits with
periods of 4.2, 38.0, and 124.0 days, and projected masses (M sini) of 5.1,
18.2, and 24.0 M_Earth, respectively. Test integrations of systems consistent
with the RV data suggest that the configuration is dynamically stable.
Depending on the effectiveness of tidal dissipation within the inner planet,
the inner two planets may have evolved into an eccentricity fixed-point
configuration in which the apsidal lines of all three planets corotate. This
conjecture can be tested with additional observations. We present a 16-year
time series of photometric observations of 61 Virginis, which comprise 1194
individual measurements, and indicate that it has excellent photometric
stability. No significant photometric variations at the periods of the proposed
planets have been detected. This new system is the first known example of a
G-type Sun-like star hosting a Super-Earth mass planet. It joins HD 75732 (55
Cnc), HD 69830, GJ 581, HD 40307, and GJ 876 as a growing group of exoplanet
systems that have multiple planets orbiting with periods less than an
Earth-year. The ubiquity of such systems portends that space-based
transit-search missions such as KEPLER and COROT will find many
multi-transiting systems.
