Recent news reports of water on Ganymede, one of Jupiter’s moons, prompted me to inquire about this.
—Ron Jacobs, Chicago
It is true. NASA scientists have detected water vapor in the atmosphere of Ganymede, Jupiter’s largest moon and the largest moon in the Solar System. But Ganymede is very cold, with temperatures reaching 300 degrees below zero. Water at the surface is frozen and one must go 100 miles below the surface to find liquid water. Ganymede is the ninth-largest object in the Solar System, with a diameter of 3,273 miles. It was discovered by Galileo Galilei on Jan. 7, 1610. It was the first time a moon was discovered orbiting a planet other than the Earth’s moon. Jupiter is the fifth planet from the sun and the largest planet in the Solar System.