Page 21 - Curriculum Visions Dynamic Book

 Io, the most volcanic body in the solar system, is seen in the highest resolution obtained to date by the Galileo spacecraft.
The smallest features that can
be seen—rugged mountains—are
2.5 kilometres across and several kilometres high. There are also plateaus and many irregular depressions, called volcanic calderas.
Several of the dark, flowlike features correspond to hot spots and may be active lava flows.
There are no landforms resembling impact craters, since the vulcanism covers the surface with new deposits much more rapidly than impacting comets and asteroids can create new craters. The picture is centreed on the side of Io that always faces away from Jupiter; north is at the top.
Io
Until the Voyager probe (page 27) reached Io, it had seemed from Earth to be an orangy-coloured moon. It is, in fact, slightly larger than the Earth’s Moon, with a diametre of 3,630 km. However, it turns out to be quite unexpected
in character. Thus, while Earth has an inactive Moon with a cratered surface that has remained unchanged for billions of years, Io is almost free of impact craters, which tells us that the surface renews itself in a geologically short time.
In fact, Io proves to be the most geologically active rocky body in the solar system, renewing its surface completely every few thousand years.
The orangy colour seen from afar also hides the great variety of colours that adorn the surface. Since sulfur can appear in yellow, black, or red forms, it is likely that the red poles are covered in one form of sulfur, while yellow sulfur dominates nearer the equator.
asteroid Any of the many small objects within the solar system.
caldera A large pit in the top of a volcano produced when the top of the volcano explodes and collapses in on itself.
comet A small object, often described as being like a dirty snowball, that appears to be very bright in the night sky and has a long tail when it approaches the Sun.
crater A deep bowl-shaped depression in the surface of a body formed by the high- speed impact of another, smaller body.
lava flow A river or sheet of liquid volcanic rock.
plateau An upland plain or tableland.
voyager A pair of U.S. space probes designed to provide detailed information about the outer regions of the solar system.
 Io is shown here as a small disk to the right of Jupiter.
/Io
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