This is the Dudley Observatory Skywatch Line for Wednesday, October 2nd, and Thursday, October 3rd, written by Louis Suarato.
The 22% illuminated, waxing crescent Moon leads Jupiter and Saturn across the sky and sets at 9:21 p.m. Wednesday. Scorpius’ brightest star, Antares shines at magnitude 1.05 below, and forms a triangle with the Moon and Jupiter. Jupiter remains in the sky until 9:52 p.m., ahead of Saturn by about 2 hours. Mercury and Venus are side by side in the civil twilight sky, and set a half hour after sunset. Look low over the west-southwest horizon for the two innermost planets. Thursday night, the Moon and Jupiter will be separated by only 1 degree. Try to observe both in the same field of view through binoculars. Mars rises in the east, about 1 hour before sunrise.
Europa is the smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 79 known moons of Jupiter. It is also the sixth-largest moon in the Solar System. Europa’s diameter is 1,940 miles, making it slightly smaller than our Moon. Europa’s icy surface makes it one of the brightest objects in the solar system. Europa is believed to have a metallic core, and a rocky core below its ice and water crust. This composition of materials indicate Europa was once entirely molten. Over time the heavier metallic materials sank to form the core, while lighter compounds floated to the surface, leaving the rocky material in between. Europa’s icy surface is scarred with cracks and ridges believed to have been caused by Jupiter’s tidal forces affecting its moon. The heating of its core, combined with the radioactive decay of rocky compounds, and the possibility of a liquid surface are conditions for biologic development. The European Space Agency is intrigued by this possibility and has proposed to launched a mission to Europa in 2022 called Icy Moon Explorer (JUICE).