This image shows the tracks left by two comet particles after they impacted the Stardust spacecraft's comet dust collector. The collector is made up of a low-density glass material called aerogel.

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 would also rate the Epoxi mission high on the list, mainly because of its flyby of comet Hartley 2. What a great view of an active comet nucleus."

In my field, the most significant robotic mission was the Stardust mission to comet Wild 2. By bringing back particles of the comet, we learned that comets are not that fundamentally different from outer belt asteroids. That opened up new ideas about the formation and early evolution of the solar system.

What do you think are the most significant events that have occurred in the past fifty years of robotic planetary exploration? Why?

Going back further in time, ESA's Giotto mission to comet 1P/Halley was a milestone, showing for the first time that comets have nuclei. This was the first time a spacecraft came close enough to look through the fog surrounding a comet. Hard to believe that was only in 1986.

In 1986, Giotto's encounter with Comet Halley provided the first ever opportunity to take images of a comet nucleus. Credits: Halley Multicolor Camera Team, Giotto Project, ESA

I would also rate the Epoxi mission high on the list, mainly because of its flyby of comet Hartley 2. What a great view of an active comet nucleus. Also, the first direct evidence of CO2 driven ejection of ice-laden dust in hyperactive comets is high on my list of favorites.

This image from the High-Resolution Instrument on NASA's EPOXI mission spacecraft shows part of the nucleus of comet Hartley 2.

Of course, the Tempel 1 impact made a big splash also.

This spectacular image of comet Tempel 1 was taken 67 seconds after it obliterated Deep Impact's impactor spacecraft.

Read More:

• Peter Jenniskens' People Profile
• Stardust Mission Page
• Giotto Mission Page
• EPOXI Mission Page
• Comets Planet Page

Last Updated: 8 August 2012