Infrared + visual-wavelength images

493

A montage of images of Jupiter

and its volcanic moon Io taken

in 2007 by the New Horizons

spacecraft during its Jupiter

fl yby on the way to Pluto and

the Kuiper belt. The prominent

bluish-white oval in the near

infrared image of Jupiter is the

Great Red Spot. The Io image

combines visual and near

infrared data, showing a major

eruption in progress on Io’s

night side at the northern

volcano Tvashtar. Incandescent

lava glows red beneath a

330-kilometer-high volcanic

plume, whose uppermost

portions are illuminated by

sunlight. The plume appears

blue due to scattering of

sunlight by small particles in

the plume. (NASA/Johns Hopkins

University Applied Physics Laboratory/

Southwest Research Institute)

Comparative

Planetology of Jupiter

and Saturn

23

Guidepost

As you begin this chapter, you leave behind the psychological security of planetary

surfaces. You can imagine standing on the moon, on Mars, or even on Venus, but

Jupiter and Saturn have no surfaces. Here you face a new challenge—to use compara-

tive planetology to study worlds so unearthly you cannot imagine really being there.

On the other hand, Jupiter and Saturn also have extensive systems of moons and rings.

Someday humans may walk on some of the moons and watch erupting volcanoes or

stroll through methane rain storms, and then journey to the rings and fl oat among

the ring particles. As you study these worlds you will fi nd answers to four essential

questions:

How do the outer planets compare with the inner planets?

How did Jupiter and Saturn form and evolve?

How is Saturn different from Jupiter?

How did Jupiter’s and Saturn’s systems of moons and rings form and evolve?

After learning about the two largest Jovian planets, in the next chapter you will

continue your trip away from the sun and visit their two smaller, and in some ways

even stranger, siblings, Uranus and Neptune. It will be interesting, but there is no place

like home.