By Dean Regas
Do planets have personalities? Venus is usually associated with the goddess of beauty. The bloody color of Mars evokes images of a war god. Mercury sprints across the sky as the winged messenger, while Saturn pokes slowly along.
But what does Jupiter do? Jupiter is just plain big. Over 88,000 miles in diameter and with a mass 318 times that of the Earth, Jupiter is easily the largest planet. More than 1,300 Earths could fit inside it. In fact, Jupiter is more massive than all of the planets, moons, and asteroids combined.
This month, Jupiter makes its closest approach to Earth for the year - roughly 400 million miles away. Despite this tremendous distance, Jupiter is very easy to identify. It is the brightest object in the eastern sky after sunset.
Dimmer than Venus, but more than three times brighter than the brightest star, Jupiter sears the heavens with a cream-colored torch. It hangs out in the constellation Leo the Lion this spring. After the sun sets, look for a sickle shape of five stars rising in the east. This is the lion's head. Three stars below and to the left of the sickle mark Leo's rear end and tail. Jupiter rests in between these two features.
Jupiter is not a solid planet like Earth. It is mostly hydrogen gas. The visible surface is actually the cloud tops above a deep layer of liquid and metallic hydrogen.
The atmosphere on Jupiter is ever changing. For a gigantic planet, Jupiter spins incredibly fast - a day on Jupiter is 10 hours. Whirled around the huge planet by this speedy rotation, the clouds channel into horizontal bands that encircle the planet. Inside the broadest band of the southern hemisphere, you can glimpse Jupiter's distinguishing mark: the Great Red Spot.
The Great Red Spot
The Great Red Spot is a churning cyclone rotating counterclockwise at more than 200 mph. Using Earth's weather as a basis, this is one huge high-pressure system. The Red Spot is so big that two Earths could easily fit inside and it's not going away. It has been there since astronomers observed it with the primitive telescopes of the 1600s.
It's hard to keep up with how many moons orbit Jupiter. Astronomers have been discovering them almost monthly. As of this writing, Jupiter has 63 moons - 47 of them were discovered since 1999. Most of the newly discovered moons are incredibly small, some around 1 mile in diameter. The four largest moons, Io, Europa, Ganymede and Callisto were discovered by Galileo in 1610. Io, Europa and Callisto are all larger than the planet Pluto, and Ganymede, larger than Mercury, weighs in as the largest moon in the solar system. These four moons always line up along Jupiter's equator and are easily visible in a small telescope.
Each moon portrays a contrasting style. Callisto is the most cratered moon with shadowy shockwaves ringing the biggest impacts. Ganymede has a combination of cratered and grooved surface features whose crust is filled with ice.
Io and Europa
Io is the most volcanic place in the solar system, with volcanoes that can send plumes of material 200 miles above the surface. Vast lakes and rivers of dark lava flow and constantly alter the surface of this moon.
Europa is similar in size to our Moon, but is completely covered by ice. The cracked surface looks like broken glass molded together with clear glue. At several locations, impacts from ancient meteors are still visible where the ice had been shattered.
The extreme tug of gravity from Jupiter and the other moons, however, cause Europa to expand and contract like an accordion. These tidal forces are transmitted into heat energy and may be enough to melt some of the interior crust. If this theory is correct, there may be a large ocean of liquid water just under the ice.
Like Saturn, Uranus, and Neptune, Jupiter has a ring system. The rings are so small that they are almost impossible to detect from Earth. Although the rings are 4,000 miles wide, they are scarcely 10 miles thick.
Most of our high-resolution images of Jupiter come from unmanned spacecrafts sent to photograph the planet. The Pioneer and Voyager missions flew by the cloud tops of Jupiter in the 1970s. But the most impressive and most detailed images came from the craft, appropriately named Galileo, which orbited Jupiter for eight years. In its odyssey around Jupiter, Galileo had close flybys of all the large moons and took some incredible pictures. Last September, with Galileo's power almost exhausted, NASA ended a spectacular mission by crashing the craft into Jupiter.
For more information on the Galileo mission and to view some out of this world's images, check out www2.jpl.nasa.gov/galileo/. Further reading: The Worlds of Galileo, The Inside Story of NASA's Mission to Jupiter (St. Martin's Press; $29.99), by Michael Hanlon.
If you go
What: Jupiter Thursday. Special evening includes viewing of planets and hourly classes on Jupiter.
When: 7-10 p.m. Thursday
Where: Cincinnati Observatory, 3489 Observatory Place, Mount Lookout.
Cost: $10, $5 students
Next up: To Mars and Beyond, 7-10 p.m. March 31
Dean Regas is the Outreach Astronomer at the Cincinnati Observatory Center. He can be reached at email@example.com
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