Potential For Life
The primary component has a metallicity of =−0.19, i.e. about 65 per cent of the solar metallicity, thus providing a probably sufficient heavy element abundance for the formation of terrestrial planets. However, no planet orbiting a member of 40 Eridani is known so far. The habitable zone of 40 Eridani A, where a planet could exist with liquid water, is near 0.68 (calculated from habitable zone) AU from A. At this distance a planet would complete a revolution in 223 Earth days (according to the third Kepler's law) and 40 Eridani A would appear nearly 20% wider than the Sun does on Earth. An observer on a planet in the 40 Eridani A system would see the B/C pair as unusually bright (magnitudes -8 and -6) white and reddish-orange stars in the night sky. This is not bright enough to diminish the darkness at night, though they would be visible in daylight (assuming an Earth-normal atmosphere). (By comparison, Earth's full moon is magnitude −12.6, and Venus at its brightest is −4.7.) It is extremely unlikely that habitable planets exist around the B star because planets circling 40 Eridani B would probably have been destroyed or sterilized by its evolution into a white dwarf. As for 40 Eridani C, it is prone to flares, which cause large momentary increases in the emission of X-rays as well as visible light. This would be lethal to life on a planet in the habitable zone.
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