The Traveling Exhibit Science Background Part B: Meet the Giants

B. Meet The Giants KEY QUESTIONS: How do we explore the giant worlds of our Solar System? How do the giant worlds compare to Earth?

Let There Be Light The Electromagnetic Spectrum Newton’s Prism

Astronomers use light as a tool Jupiter at different wavelengths Ultraviolet images in the ultraviolet show Jupiter's auroral emissions Visible What our eyes would see from a spacecraft or a distant moon Infrared Bright areas in the infrared show heat escaping through gaps in the clouds

Giant Worlds are GIANT Compared to the rocky worlds of the inner Solar System, the giant worlds are enormous. The largest of them, Jupiter, is so big that more than 10 Earths could line up across its diameter; more than 1,000 Earths could fit inside; and all the other planets in the Solar System put together are less than half its tremendous mass. The other giant worlds are not as big as Jupiter, but they still dwarf rocky planets like Earth.

Some facts about the Giant Planets

Giant Planets have NO SOLID SURFACE You could not land a spaceship on a Giant Planet!

Storm Warnings The Great Red Spot on Jupiter is 20,000 km long and has been followed by observers on Earth since the telescope was invented 400 years ago. This huge storm is made visible by variations in the composition of the cloud particles.

The Greater a Planet’s Axial Tilt, the More Extreme its Seasons A planet has seasons if its axis of rotation is tilted relative to its orbital plane. The tilt causes the amount of sunlight reaching the planet to vary from place to place. Earth’s axis is tilted by 23.5°, producing our familiar pattern of seasons. By contrast, Uranus is tilted by more than 90°, which produces very extreme seasons indeed. Extreme Seasons - Uranus

Wild Weather on Neptune The Sun at Neptune is 900 times dimmer than at Earth. Since heat from the Sun drives weather, the winds on Neptune should be relatively mild. Instead, they whip around at more than 2,000 km per hour. The weather is correspondingly wild, with enormous dark storms that come and go, and high-altitude white thunderheads that bubble up from the depths of Neptune’s thick hydrogen atmosphere. Heat from Neptune itself may drive these storms.

Fran Bagenal University of Colorado Exploring the Giant Magnetosphere of Jupiter

Earth Jupiter's strong magnetic field makes a vast magnetosphere ~100 Jupiter Radii 1000 Suns would fit inside Jupiter's magnetosphere

Solar Wind Magnetosphere ~10 Earth Radii Earth

Earth Aurorae If you’ve ever seen the beautiful northern lights on Earth, then you’ve witnessed visible evidence of an enormous, invisible phenomenon: Earth’s magnetic field. Polar lights, or aurorae, happen on any planet that has a magnetic field and an atmosphere. The glow is caused when charged particles guided by the magnetic field collide with atoms in the atmosphere and stimulate the emission of light.

Earth Aurorae

Jupiter's 3 Types of Aurora Aurora associated with moons Steady Main Auroral Oval Variable Polar Aurora

Saturn also has a large magnetosphere and aurorae

All Giant Planets Have Rings Jupiter UranusNeptune Saturn but only Saturn’s are visible

Fun Facts Planetary rings are not solid. Instead, they are made of countless ice and rock fragments, ranging in size from dust particles to house-sized boulders. Saturn’s diameter is more than 9 times that of Earth, and yet its ring system is only about 50 meters thick! This means that if Saturn were the height of a 60-story building, the rings would be as thin as a sheet of paper.

Rings Up-close This false-color image of Saturn's main rings was made by combining data from multiple star occultations using the Cassini ultraviolet imaging spectrograph. During occultations, scientists observe the brightness of a star as the rings pass in front of the star. Cassini has given scientists the most detailed view yet of Saturn's densely packed B ring. Particles in the central yellow regions are too densely packed for any starlight to pass through. A Cassini image of Saturn. The Sun is behind the planet, putting Cassini in shadow. Earth is the bright dot outside the main rings at the ten o’clock position.

Many Moons The giant planets each have many moons ranging in size from rocky bodies only a few kilometers across to one that is larger than Mercury. New moons are being found all the time. Let’s meet some of them. Saturn’s Moon Rhea

Europa An icy moon of Jupiter, Europa is covered with a thick layer of ice. Beneath the ice lies a massive saltwater ocean which might harbor life. Image taken by Voyager 2 spacecraft Credit: NASA/JPL

Io This moon of Jupiter is the most volcanically active body in the solar system. Eruptions tower over the surface, as seen here in this edge-on view of a 90-mile high plume. The surface of Io is constantly changing, so no craters exist today. Image taken by Voyager 2 spacecraft Credit: NASA/JPL

Enceladus An icy moon of Saturn, Enceladus boasts a myriad of large fractures – dubbed “tiger stripes” by the imaging scientists – that appear to spout massive geysers of liquid water, as seen in the false color image below. Like Jupiter’s Europa, Enceladus is now a potential habitat for life within our Solar System. Images taken by Cassini spacecraft Courtesy NASA/JPL/Space Science Institute

Titan This moon of Saturn, bigger than the planet Mercury, boasts a thick, methane-rich atmosphere, seen here as the purple band around the limb. It is believed that our primordial Earth had an environment very similar to Titan’s. Image taken by Cassini spacecraft, courtesy NASA/JPL.

B. Meet the Giants SUMMARY Jupiter, Saturn, Uranus, and Neptune are mini solar systems. Each has a collection of many moons and a ring system. Planetary rings are not solid. Instead, they are made of countless ice and rock fragments, ranging in size from dust particles to house-sized boulders. Each giant planet is surrounded by an enormous magnetic field that is invisible except near the poles, where magnetized particles show up as spectacular aurorae. Our eyes see only a narrow range of the light filling the Universe. However instruments allow us to detect light waves that are longer or shorter than our eyes can see. Wavelengths of light reveal different things about an object such as what it’s made of. We might be more likely to find life on or in some of the moons of the giant planets than on any of the terrestrial planets besides Earth.

CONCLUSION Re-visiting the Big Ideas of the Introductory Presentation We study the giant planets of our Solar System because they tell us about the formation of solar systems, our planet, and the conditions necessary for life. Someday we may answer the age- old question of whether there is life beyond Earth. We are developing extraordinary new tools, techniques, and insights for exploring these extraordinary worlds – mini solar systems that include many moons and spectacular rings.

There are two possibilities: Maybe we’re alone… Maybe we’re not… Both are equally amazing…

We shall not cease from exploring, And the end of all our exploration Will be to arrive where we started And to know the place for the first time. - T.S. Eliot, Little Gidding