Wednesday, September 22, 2010

Jupiter Opposition 2010

Better late than never. Check out Jupiter, now at opposition! 

I realize that I told you about the opposition of Uranus without evening mentioning the simultaneous opposition of one of the most prominent objects in our nighttime sky--the planet Jupiter. Jupiter’s opposition for this year occurs over September 20-21, but if you cannot see it tonight, check it out over the next evening or two. It will still be just as beautiful. Jupiter will be rising in the east as the sun sets in the west. Only Earth’s moon will be brighter than Jupiter.

A composite of 4 images of Jupiter, taken December 7, 2000 by the NASA Cassini spacecraft. The moon Europa is casting a shadow on the planet at the lower-left. Image Credit: NASA/JPL/University of Arizona

Earth’s encounters with Jupiter happen every 13 months when Earth--the inner planet--laps Jupiter in their race around the sun. Earth and Jupiter do not orbit the sun in perfect circles, so they are not aways the same distance apart when Earth passes. On September 20-21, Jupiter will be as much as 75 million km closer than in previous encounters and will not be this close again until 2022.

When viewed through a telescope, the disk of Jupiter can be seen in rare detail. For instance, the Great Red Spot, a cyclone about twice as wide as Earth, is bumping against a smaller storm which has been nicknamed “Red Spot Jr.” 

In addition, Jupiter’s distinctive South Equatorial Belt recently vanished, possibly submerged beneath high clouds. Astronomers suggest that it could reappear at any time, accompanied by many new spots and swirls, all visible in backyard telescopes.

And amateur astronomers have recently reported a significant number of fireballs in Jupiter’s atmosphere. This is the apparent result of many small asteroids or comet fragments that are hitting Jupiter and exploding among the clouds. Researchers of these events have suggested that observers could see visible flashes as often as a few times a month.

Of course, we must not forget the four largest moons of Jupiter, which are visible even with a modest pair of binoculars. Since Galileo Galilei’s discovery of these planet-sized worlds 400 years ago, we have learned that one has active volcanoes (Io), one possibly has underground oceans (Europa), one has vast fields of craters (Callisto), and one has mysterious global grooves (Ganymede). In modern amateur telescopes, these appear as planetary disks with colorful markings.

A “family portrait” of Jupiter and its four largest moons. From top to bottom, the moons shown are Io, Europa, Ganymede and Callisto. The image is a composite, with the size of the moons and the planet in scale. The images of all but Callisto were taken by the NASA Galileo spacecraft. The orbital path of Galileo and the nature of the study of Callisto prevented a good image of the moon as a whole. The image of Callisto seen here was taken in 1979 by the NASA Voyager spacecraft. Image Credit NASA

More on Jupiter

Jupiter is the fifth planet from our sun and the largest planet in our solar system. Jupiter is a gas giant, having a mass a little less than 1/1000 that of the sun while 2-1/2 times the mass of all the remaining gas giants--Saturn, Uranus, Neptune. These four are are sometimes described as the Jovian planets--the planets that share many of the characteristics of Jupiter (Jove).

Quick trivia, by Jove! The king of the Roman gods was first called Jove. Later he was described as Father Jove--in Old Latin, “Jovis Pater.” Over the generations this phrase was gradually slurred and abbreviated, becoming Jupiter.

As seen from Earth, Jupiter reaches an apparent magnitude of -2.94--on average, the third-brightest object in our sky after Earth’s moon and Venus. 

One quarter of Jupiter’s mass is helium, with rest being mostly hydrogen. Astronomers think there may be a rocky core of heavier elements. Jupiter has a very rapid rotation, causing the planet to bulge at the equator, a shape known as an oblate spheroid. Jupiter’s outer atmosphere is divided into several bands at different latitudes, with storms along the boundaries of each of the bands. One result is the prominent feature known as the Great Red Spot, a giant storm that has existed at least since the seventeenth century, when it was first observed by telescope. Jupiter is surrounded by a faint ring system and a powerful magnetosphere. And as of this writing, Jupiter has at least 63 moons, including the four large Galilean moons--those moons first observed in 1610 by Galileo Galilei. They are Ganymede, Callisto, Europa, and Io. The largest of these is Ganymede, having a diameter greater than the planet Mercury.

This time-lapse video records the Voyager 1 spacecraft’s approach to Jupiter during a period of over 60 days, prior to its closest approach on March 5, 1979. Image Credit: NASA/JPL

The planet Jupiter has been explored by several NASA robotic spacecraft. In chronological order, they are Pioneer 10 (flyby 1973), Pioneer 11 (flyby 1974), Voyager 1 (flyby 1979), Voyager 2 (flyby 1979), Galileo (orbiter 1995-2003), Cassini (flyby 2001), and New Horizons (flyby 2007). 

Future Mission, Juno

Currently in development is the NASA Juno mission to study how Jupiter formed and became the dynamic world we see today. The solar-powered Juno spacecraft will map the gravity field, magnetic field and atmospheric structure of Jupiter from a unique polar orbit. Juno's observations will lead to a better understanding of the formation of our solar system and planetary systems discovered around other stars.

Artist concept of the Juno spacecraft at Jupiter. Image Credit: NASA/JPL

The Juno mission launch window opens August 5, 2011. The spacecraft will then undergo a five-year cruise, arriving at Jupiter in July of 2016. Once at Jupiter, the spacecraft will spend the next year orbiting the planet 32 times. Specifically, Juno will...

1. Determine how much water is in Jupiter’s atmosphere, which helps determine which planet formation theory is correct, or whether a new theory is needed

2. Look deep into Jupiter’s atmosphere to measure composition, temperature, cloud motions and other properties

3. Map Jupiter’s magnetic and gravity fields, revealing the planet’s deep structure

4. Explore and study Jupiter’s magnetosphere near the planet’s poles, especially the auroras--Jupiter’s northern and southern lights--providing new insights about how the planet’s enormous magnetic force field affects its atmosphere.

To learn more about the planet Jupiter, past missions and future missions, check out these links.

NASA Solar System Exploration - Jupiter

NASA Solar System Exploration - Galileo Legacy Site

NASA Juno Mission


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