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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“Genius is no more than childhood recaptured at will, childhood equipped now with man’s physical means to express itself, and with the analytical mind that enables it to bring order into the sum of experience, involuntarily amassed.”
—Charles Baudelaire (1821–1867)