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With Explore the Planets, investigate the planets, their moons, and understand the processes that shape them. By G. Jeffrey Taylor, Ph.D. See our DVD collection.
This Galileo image of Prometheus is similar to the original Voyager picture.
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NASA

Io Discoveries with Voyager

When Voyager flew by Jupiter, there was little expectation that the moon, Io, would exhibit active volcanism. The exception was a prediction, by three brave scientists, that Voyager would find evidence that Io might be hot enough for volcanoes. The paper explained reasons for the excess heating of Io, and was published just two weeks prior to the Io encounter.

To everyone's surprise, when Voyager passed by, it actually caught the Prometheus geyser going off.

Later the three scientists who made the prediction were asked why they had not waited 2 weeks, until after Voyager's encounter, to publish the paper, to avoid the risk of being wrong. They replied that they had full confidence in their prediction.

The Galileo mission to Jupiter continues the exploration of the volcanism of Io.


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Traveling Nitrogen Classroom Activity Kit

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Voyager

The rare geometric arrangement of planets Jupiter, Saturn, Uranus, and Neptune in the 1980's made it possible for the Voyager spacecrafts to visit them over a 12 year span instead of the normal 30. They...more

Galileo

The Galileo spacecraft was launched on October 19, 1989. Galileo had two parts: an orbiter and a descent probe that parachuted into Jupiter's atmosphere. Galileo's primary mission was to explore the Jovian...more

Amalthea

Amalthea was discovered by E Barnard in 1872. Of the 17 moons it is the 3rd closest to Jupiter, with a standoff distance of 181,300 km. Amalthea is about the size of a county or small state, and is just...more

Callisto

Callisto was first discovered by Galileo in 1610, making it one of the Galilean Satellites. Of the 60 moons it is the 8th closest to Jupiter, with a standoff distance of 1,070,000 km. It is the 2nd largest...more

Evolution of Callisto

Most of the moons and planets formed by accretion of rocky material and volatiles out of the primitive solar nebula and soon thereafter they differentiated. Measurements by the Galileo spacecraft have...more

Very Large Impact Crater

Many examples of the differing types of terrain are shown in this image. In the foreground is a huge impact crater, which extends for almost an entire hemisphere on the surface. This crater may be compared...more

Surface of Callisto

The surface of Callisto is deeply pockmarked with craters. It looks to be perhaps the most severely cratered body in the solar system. There are also very large craters to be found there. The severity...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF