Physical Characteristics
The motion of the parent star indicates a minimum mass for Gliese 581 d of 5.6 Earth masses (earlier analyses gave higher values). Dynamical simulations of the Gliese 581 system assuming that the orbits of the three planets are coplanar show that the system becomes unstable if the masses of the planets exceed 1.6 – 2 times the minimum values. Using earlier minimum mass values for Gliese 581 d, this implies an upper mass limit for Gliese 581 d of 13.8 Earth masses. The composition of the planet, however, is not known.
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“A man’s thinking goes on within his consciousness in a seclusion in comparison with which any physical seclusion is an exhibition to public view.”
—Ludwig Wittgenstein (1889–1951)