GJ 3021 b is an extrasolar planet approximately 57 light-years away in the constellation of Hydrus. The planet is a Jupiter-like planet orbiting about 0.5 AU from its star with a minimum mass 3.37 times that of Jupiter, as determined by measuring variations in the radial velocity of the star. A study published in 2001 suggested that the usual inability to determine the orbital inclination of an extrasolar planet through radial velocity measurement had caused this mass to be severely underestimated. The astrometric orbit gives an orbital inclination of 11.8° and a mass of 16 Jupiter masses, which would make the object a brown dwarf. However later analysis showed that Hipparcos was not sensitive enough to accurately determine astrometric orbits for substellar companions, which means the inclination (and hence the true mass) of the planet are still unknown.