In his 1941 short story Nightfall, Isaac Asimov describes a planet called Lagash that resides in a multistar system. Constantly illuminated from all sides by its, count 'em, six suns, Lagash experiences dark skies for just a few hours once every 2,000 years. In the story the rare celestial alignment occurs and darkness descends for the first time in living memory - at which point the inhabitants of Lagash go berserk and burn their cities.
Nightfall was sci-fi, but we now know the kinds of multistar planetary systems it describes are real - and more common than once thought. For example, astronomers recently realized that a planet-hosting star system has four suns, the second of its kind ever found. The finding is in the Astronomical Journal.
Our galaxy contains hundreds of billions of stars, and astronomers suspect planets accompany almost all of them. This latest work implies that about 4% of sunlike stars may exist in quadruple systems. That's a lot of potential Lagashes.
The system just found, called 30 Ari, is 136 light-years from Earth, in the constellation Aries. We had known of three stars there as well as a planet 10 times bigger than Jupiter. The fourth star is the new discovery.
The system is arranged as two binary pairs that orbit each other at a distance more than a thousand times that between the Earth and our sun. The known planet orbits one star in one pair. Its sky would contain two suns, and the more distant binary pair would appear as two very bright stars, visible even during daylight. If the planet and all four of 30 Ari's stars are coplanar, night could come to one hemisphere of the world only once every several millennia, when all four stars briefly align on the opposite side. But put aside any Asimovian fears. Life as we know it could not exist on the gas-giant planet, and its nearby suns would incinerate any cities all on their own. No frenzied inhabitants required.
