  We report the detection of the lowest mass extra-solar planet yet found
around a Sun-like star - a planet with an \msini of only 14.21 $\pm$ 2.91 Earth
masses in an extremely short period orbit (P=2.808 days) around $\rho^{1}$
Cancri, a planetary system which already has three known planets. Velocities
taken from late 2003-2004 at McDonald Observatory with the Hobby-Eberly
Telescope (HET) revealed this inner planet at 0.04 AU. We estimate an
inclination of the outer planet $\rho^{1}$ Cancri d, based upon {\it Hubble
Space Telescope} Fine Guidance Sensor (FGS) measurements. This inclination
suggests an inner planet of only 17.7 $\pm$ 5.57 Earth masses, if coplanarity
is assumed for the system.
