Aspetti didattici. 2. Attività

You are cruising in the troposphere of Saturn under the most magnificent ring structure in the solar system. Few sights are more astounding. The white, icy rings soar 75,000 kilometers above your head. Ringshine illuminates everything around you. No fewer than six crescent moons rise in the sky. The light from the setting sun scatters against a mist of ammonia crystals, forming a beautiful sun dog. You are buffeted by ammonia clouds that stream by you at speeds greater than 1,500 kilometers an hour. These are some of the fastest winds in the solar system. More than 30,000 kilometers below you, with pressures no human-made thing could survive, is a global ocean of liquid metallic hydrogen. There will be no landing on this planet.

The sheer scale of the solar system's largest anticyclone is difficult for a traveler to grasp. From this vantage point, only a small part of Jupiter's Great Red Spot (left) can be seen. It rises at least eight kilometers above the surrounding clouds. Lightning bolts that could pulverize a city crackle at its base into the lower clouds. Winds at the outer edge of the anticyclone swirl at more than 400 kilometers an hour. The spot rotates counterclockwise once every seven days. The turbulence created by this mega storm is brutal, the sound, deafening. At least two planets the size of Earth could fit inside this monstrous storm, which has been spinning in Jupiter's southern hemisphere for at least 400 years. There is no sign that it will stop.

People have been known to fall to their knees and weep at the sight of Arizona's Grand Canyon. One wonders what the first traveler to the Mariner Valley will do when gazing into this canyon. At almost four miles deep and so wide that in some places you would have to strain to see the other side, this gigantic tectonic crack would span the U.S. from New York to California—a quarter of the way around the planet—so that sunrise at one end happens six or so hours before sunrise at the other. Water once ran through large segments of this expanse. In this image the traveler views an icy mist filling the valley as the suns sets over the north rim.

You feel it before you see it: an ominous rumble, reverberating deep in your chest and up from your feet. There is no sound here. And then the eruption comes: two huge ice plumes explode through the surface of Enceladus, spewing ice crystals into space at more than 1,000 miles per hour. The silent violence is lit by our distant sun. With just 1/16 of our own moon's gravity, Enceladus will not be an easy world to tread on; hikers may need to strap on jetpacks and take care to avoid the valleys that give birth to the powerful geysers.

The Geysers of Triton

Visitors to the largest of Neptune's moons, Triton, will be treated to an array of cryogeysers that are probably composed of nitrogen frost and dark organic compounds. The smoky-looking geysers might be heard from kilometers away as they stream more than 8,000 meters into the thin atmosphere before their tops are whisked away by prevailing winds. Methane and nitrogen ice cover this world whose surface temperature plummets to almost —200 degrees Celsius.

Peaks of Eternal Light

Not far from home, on our own moon, a unique condition exists (below). Discovered in 1994 on Peary crater near the north pole, the so-called peaks of eternal light are the only known region in the solar system where the sun never sets. (Other such regions may exist on Mercury but have not been seen yet.) This unusual condition arises because the moon's rotational axis is barely tilted relative to the plane of its and Earth's orbit around the sun. Certain to become a tourist attraction, this site may one day also house the first moonbase. Temperatures in the area fluctuate comparatively little, perhaps by 20 degrees, making it an ideal place to settle. The possibility of water ice here is an added bonus.

Herschel Crater on Mimas

Adventurous climbers who ascend the peak at the center of Herschel crater (left) on Saturn's moon Mimas will find themselves more than 6,000 meters above the chasm's floor. Surrounded by the crater walls, which rise majestically to almost 5,000 meters, and with Saturn setting in the background, travelers might wonder how Mimas survived the impact that formed this 139-kilometer-wide depression, which is almost a third of the satellite's diameter.

Sunrise on Mercury

Sunrise and sunset on Mercury are spectacles to behold. Two and one half times larger in the sky than seen on Earth, the sun appears to rise and set twice during a Mercurian day. It rises, then arcs across the sky, stops, moves back toward the rising horizon, stops again, and finally restarts its journey toward the setting horizon. These aerial maneuvers occur because Mercury rotates three times for every two orbits around the sun and because Mercury's orbit is very elliptical.