description HD 128311 c Overview
HD 128311 c is a gas-giant exoplanet orbiting the K-type star HD 128311, located roughly 53 light-years from Earth. The planet was announced in 2005 from radial-velocity observations. It is the outer member of a known two-planet system, and its orbital period is close to twice that of HD 128311 b, producing a relationship described as a 2:1 mean-motion resonance.
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What is HD 128311 c's orbital period and mass?
HD 128311 c takes about 922 days to orbit its star and has a minimum mass around 3.1 to 3.2 Jupiter masses. That makes it the more massive outer companion in the pair.
Why is HD 128311 c said to be near a 2:1 resonance with b?
Planet b's period is about 453 days and c's is about 922 days, so c takes roughly twice as long to complete an orbit. The ratio is close to, but not exactly, 2:1, and planetary interactions can make such systems dynamically interesting.
How was HD 128311 c detected?
It was first reported in 2005 from radial-velocity observations, with later astrometric information also appearing in the archive. The method measures the host star's wobble and does not by itself give a directly imaged surface.
How far away is HD 128311 c's host star?
HD 128311 is a K-type star about 53 light-years from Earth, and c is its outer known planet. Its roughly 1.74 AU orbit is far wider than Earth's orbit around the Sun, even though the planet itself is a gas giant.
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