Should you look southeast after 9 p.m. this month and see a very bright, unmoving light in the sky, don’t call in a UFO sighting. You are looking at Jupiter, the largest planet in our solar system. Aptly named for the chief god in the Roman pantheon, it accounts for more than two-thirds of all the material in the solar system outside of the Sun.

On Sept. 20, Jupiter will be 367 million miles from Earth, its closest approach since 1963. In recognition of that, let us take a look at Jupiter, a couple of its moons, and a NASA mission scheduled for launch in August of 2011.

We start with the planet itself. First, a few dry facts for perspective. Jupiter is a gas giant composed mostly of hydrogen and helium. It is 11 Earth-diameters wide, has 318 times the mass of Earth, and 1,300 Earths could be packed into its volume.

Now for the more interesting stuff! Jupiter’s atmosphere is a churning cauldron of turbulence. Winds traveling at speeds that can exceed 400 miles an hour roar in bands across its atmosphere. Hurricane-like storms come, go and stay. A conspicuous feature called “The Great Red Spot” is a giant storm, shaped like a football and large enough to swallow two to three Earths – and it has been raging for at least 300 years.

The latest count shows Jupiter to have 62 moons, but they are an odd lot. Four are quite large and the rest are fairly small, with none that might be called midsized. Ganymede, the largest, is in fact bigger than the planet Mercury. The smaller ones are most likely captured asteroids. Of the four large ones, two are of particular interest and they couldn’t be more different. Let me introduce you to Europa and Io.

With a diameter of 1,900 miles, Europa is slightly smaller than our Moon. But unlike the Moon’s pockmarked surface, Europa has a smooth icy crust. This surface is traversed by brown lines called lineae. Some of these lineae are 12 miles wide and their origin is cause for much discussion. But it is generally accepted that there is a salty ocean beneath Europa’s crust and the linea are cracks caused by ocean movements and upwelling.

Now for a very different place, Io can best be described as exotic. It has a diameter of 2,263 miles and a surface that looks like a pizza. It has been said that Io turns itself inside out every few years. This is due to rampant volcanism – it has at least 400 active volcanoes. Because of low gravity and no atmosphere, these can shoot plumes 200 to 300 miles high. The resultant ash and lava flows coat the surface with yellow, red, white, and black splotches.

We will have to wait for space missions currently on the drawing board before we see any spacecraft visit these moons. However, a mission to visit Jupiter itself is getting ready to launch. This is Juno, and its scheduled launch window is Aug. 11–31, 2011 with a projected date of arrival at the distant planet in October 2016.

Upon arrival, the spacecraft will go into polar orbit (flying over the north and south poles). The mission is designed to answer a number of questions regarding Jupiter’s make-up, which will lead to a better understanding of our solar system’s origins.
So when you next look up at Jupiter. perhaps you will see more than just a
bright light.

Keith Turner will return for special editions of Starry Skies whenever an astronomical event worth reporting is on the horizon. A retired physicist, Keith is a longtime Marina resident and Marina Times contributor.