Early models of the Universe placed the Earth at the center, with the Sun and planets revolving around it. In 1609, Galileo started looking at the night sky through a telescope. When he observed the planet Jupiter, he found it was surrounded by several small moons that orbited around it. This suggested that not everything revolved around the Earth. In this way, Jupiter redefined how we consider our place in the Universe.
It takes Jupiter 11.9 Earth years to complete one revolution around the Sun. A day, however, is only 9.9 hours long. This rapid rotation causes an equatorial bulge that is visible when you view the planet through a telescope.
The banded appearance reflects the presence of strong atmospheric currents which have different rotation periods at different latitudes. These bands get their lovely pastel colors from clouds, including the famous Great Red Spot. These colors come from lightning discharges and heat, and some of the chemical compounds may be related to organic molecules that formed on ancient Earth as a prelude to the origin of life.
The darker brown strips across Jupiter are called belts, the brighter strips are zones. Belts are darker because they are cooler, settling lower into the atmosphere.
The belts themselves are more than 200,000 miles wide each. After Jupiter emerged from behind the Sun in 2010, it was mysteriously missing the South Equatorial Belt. Astronomers are uncertain what causes this phenomenon, but it has happened before: in 1973 and again in the early 1990s. In both cases, the planet kept its appearance for a few weeks until the belt eventually returned.
This planet has no solid surface: it is entirely liquid and gas. The surface that we see comes from the uppermost layer of its ever-changing atmosphere, composed of thick clouds of hydrogen and helium.
Although the clouds are all anyone ever sees of Jupiter, they constitute less than 1 percent of the planet's total radius. Underneath the clouds the atmosphere grows denser and hotter under the pressure. Here methane, ammonia, and other trapped gasses may be crushed into tiny rocks, until they eventually cease to behave as gasses. Five thousand miles down, the atmospheric pressure is a million times what it is on Earth. Here liquid hydrogen is compressed into a shiny, metallic substance.
Scientists have fabricated only tiny quantities of metallic hydrogen here on Earth, which has helped explain certain aspects of Jupiter's nature. Its magnetic field is twenty thousand times as strong as Earth's, and extends all the way to Saturn. The presence of highly unstable metallic hydrogen in the core may also be a factor in causing all the electrical storms which are constant in the planet's atmosphere.
There are lots of great books about outer space. My favorite is Astronomy: A Visual Guide, by Mark A. Garlick. It's filled with interesting information and lots of beautiful photographs.
For my previous posts on outer space, click here. For a look at Jupiter's first four known moons, click here.
Always worth checking out is the Hubble Space Telescope, which celebrated its twentieth anniversary last month.