There are eight impact sites visible in this image of Jupiter by NASA's Hubble Space Telescope's Planetary Camera.

What do you think are the most significant events that have occurred in the past fifty years of robotic planetary exploration? Why?
I think the Voyager 1 and 2 grand tour would have to be my choice for one of the greatest moments in NASA robotic history from the past 50 years. It is significant for several reasons. First of all, it was really our first foray into very deep space exploration.

"I think some of the greatest discoveries have come when we found the unexpected, or were just in the right place at the right time."

The Voyagers were engineering and mathematical marvels to be able to survive the trip, and to take advantage of the unique planetary alignment to visit all four giant planets (Voyager 2). They also communicated over such vast distances back to us. The triumph of their design is that we still hear from them today as they are poised to enter interstellar space!

The Voyagers have also provided great scientific advances: they were the first to explore worlds very different from Earth and give us views of their intriguing atmospheres, rings and moons. They really set the stage for planetary Flagship missions to follow, like Galileo and Cassini.

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?

I think some of the greatest discoveries have come when we found the unexpected, or were just in the right place at the right time. In my field, Jovian planet atmospheric study, there have been several events that come to mind:

1) Comet Shoemaker-Levy 9, and the impact of its fragments into Jupiter, followed by smaller impacts 15 years later. While they helped us understand parts of the atmosphere, they also allowed us to better illustrate that the solar system isn't static; it is a dynamic place where storms rage, impacts happen and volcanoes erupt.

These NASA Hubble Space Telescope snapshots reveal an impact scar on Jupiter fading from view over several months between July 2009 and November 2009.

2) New Horizons viewing Jupiter during a global cloud "upheaval," where usual thick clouds at the equator had disappeared. This allowed us to see clear high altitude waves and measure their speed for the first time. This helps us understand motions and structure below the clouds, where we can't usually probe.

With its Multispectral Visible Imaging Camera (MVIC), half of the Ralph instrument, New Horizons captured several pictures of mesoscale gravity waves in Jupiter's equatorial atmosphere as seen in this image.

3) The unprecedented coverage of Saturn by Cassini. The amount of data has been incredible, and we will be analyzing it for years to come, but we've already seen a warm, hurricane-like, polar vortex at the south pole, a hexagon shaped flow structure around the north pole and a massive, planet-encircling storm in the northern spring season.

NASA's Cassini spacecraft captures a composite near-true-color view of the huge storm churning through the atmosphere in Saturn's northern hemisphere.

I also like Cassini's image of the water ice plumes from the south pole of Enceladus.

Giant plumes of ice were photographed in dramatic fashion by the Cassini spacecraft during a flyby of Saturn's moon Enceladus. Numerous plumes are seen rising from long tiger-stripe canyons across Enceladus' craggy surface.

Read More:

• Amy Simon-Miller's People Profile
• Voyager 1 Mission Page
• Voyager 2 Mission Page
• Cassini Mission Page
• Jupiter's Planet Page
• Saturn's Planet Page
• Enceladus' Moon Page

Last Updated: 12 April 2013