Except for the moon, Jupiter is the brightest celestial object in the sky this week. Tonight, in fact, the biggest planet in our solar system is the closest it ever gets to Earth, approximately 368 million miles (the maximum distance is about 601 million miles). The last time it was so near was 1963, and if you miss the gas giant’s closeup, you’ll have to wait until 2022 for another opportunity.
Jupiter is in direct opposition to the sun, which means the Earth passes in between the two. Jupiter will appear in the eastern sky just after sunset, rising higher as the evening progresses. The best viewing is around midnight. With a handheld telescope, you can also see Uranus in the other direction.
Here a few things to know about our giant sibling.
The moons of Jupiter
In 1610, Galileo Galilei built his own “occhiale,” or telescope, and with it he observed Jupiter’s many moons and particularly their remarkable habit of orbiting something other than Earth, which provided big points for the Copernican theory. Galileo originally called Jupiter’s moons the “Medicean planets” after the powerful Medici family. German astronomer Simon Marius claimed to see them first, but since Marius published his work later, Galileo gets the credit. It was Marius who, after a conversation with astronomer Johannes Kepler, suggested the names Io, Europa, Ganymede and Callisto, all former loves of the god Jupiter. At last count, Jupiter has 63 moons.
This spring, astronomers discovered that Jupiter’s bottom stripe, or its South Equatorial Belt, was missing. It had been fading, but astronomers didn’t expect it to vanish completely. NASA scientists theorize that white ammonia clouds are hiding the stripe. The distinctive brownish orange stripes are actually clouds of sulfur, phosphorus and other gases. Jupiter’s SEB has faded in the past, from 1973 to 1975, from 1989 to 1990, and in 1993 and 2007. Based on those trends, scientists think the SEB will return in the next two years. The stripe typically returns in a dramatic fashion, beginning at a single point and rolling out so fast and big that even amateur astronomers can see it with small telescopes.
The buckle in that belt, the Great Red Spot, is a high-pressure hurricane-like storm. About three times the size of Earth, the spot spins counterclockwise at a rate of 225 mph, completing an orbit every six days. According to NASA, the spot has been shrinking since it was first seen in the 17th century by Galileo. Recent observations of the spot reveal that its structure is more complicated than previously thought.
Like Saturn, Uranus and Neptune, Jupiter has rings that circle its equator. Much fainter than Saturn’s, these rings are probably made of fine dust particles, and the largest is about 20 miles thick and more than 4,000 miles wide. It encompasses the orbit of two small moons.
Life on Europa?
Europa, Jupiter’s fourth largest moon, is believed to host a large sub-surface ocean of water, hidden beneath miles of ice, which could be rich in oxygen and might support life. Scientists theorize that radiation from Jupiter’s magnetosphere strikes the ice and releases oxygen. There is also the possibility of underwater volcanic activity, which could stimulate conditions for life to begin. Recently, scientists found life forms deep in the Earth’s ocean thriving in conditions without light or oxygen, instead feasting on nutrients from hydrothermal vents. Some scientists think this is how life originated on Earth, and may also be a way for Europan life to evolve.
For a high-resolution look at Jupiter, click here to see our Photo of the Day.