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50 Years of Robotic Planetary Exploration: William Sjogren, Senior Research Scientist (Retired), Jet Propulsion Laboratory
28 Dec 2012
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What do you think are the most significant events that have occurred in the past fifty years of robotic planetary exploration? Why?

Many exciting things were made known through robotics.

For example, the moon's surface was solid and not like a place in a fairy tale where one would sink into nowhere. It is true that we did not find any aliens on the moon or Mars. However, we now know about the detailed structure of the atmosphere and ionosphere of Mars and Venus, the soil composition of the moon and Mars, the attributes of the many satellites of Jupiter and Saturn, and about the volcanoes on Jupiter's moon Io.

We also know what the far-side of the moon looks like, how different Jupiter's Galilean satellites are and that there may be oceans beneath the surface of Europa. It sure was an exciting time or me: 1962 - 1999, of course it still is an exciting time for me.

In your field of work, what are some examples of the great achievements and discoveries in planetary science and robotic exploration throughout the past 50 years?

The most exciting planetary finding, for me, was the discovery of the Mascons on the moon and Mars with my colleague, Paul Muller; for it changed geologists and geophysicists' ideas about the interior structure of these bodies.

Gravity highs were supposed to be in the mountains and highlands, and not in the lowlands or large basins with depressed topography -- a completely new phenomenon. And from this, many new ideas emerged to explain these results.

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