NASA's Hubble Space Telescope took this iconic image of the Eagle nebula, dubbed the "Pillars of Creation," highlighting its finger-like pillars where new stars are thought to be forming.

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

"I never cease to be impressed, as Carl Sagan was, at how well the two Voyager spacecraft performed."

Hubble is robotic in a sense, but it was serviced by humans. I am a big admirer of both manned and unmanned spaceflight. They both have their purposes and sometimes, as with Hubble, they can combine and produce really spectacular results.

Several hundred never before seen galaxies are visible in this "deepest-ever" view of the universe, called the Hubble Deep Field (HDF), made with NASA's Hubble Space Telescope.

The Hubble has done more for the field of astronomy than any other mission. It's, on a scientific basis, easily NASA's most successful science mission ever. Of course it has been up there for 20 years, so it should be.

Jupiter's faint ring system is shown in this color composite as two light orange lines protruding from the left toward Jupiter's limb. The Voyager 2 spacecraft was at a range of 1,450,000 km (900,000 miles) and about two degrees below the plane of the ring when it took this image.

There have been some other very spectacularly successful missions. I think that I would rank the Voyager missions to the outer planets right up there.

This is an enhanced, false-color view of Saturn by Voyager.

Voyager was a tremendous technical achievement. It was thirty years ago when they did the grand tour of the solar system.

This farewell shot of crescent Uranus was taken by Voyager 2 as it departed from the planet on 25 January 1986. This image was taken at a range 600,000 miles.

"Look again at that dot," Carl Sagan wrote in his book "Pale Blue Dot." "That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every 'superstar,' every 'supreme leader,' every saint and sinner in the history of our species lived there -- on a mote of dust suspended in a sunbeam."

I never cease to be impressed, as Carl Sagan was, at how well the two Voyager spacecraft performed.

The existence of oceans or lakes of liquid methane on Saturn's moon Titan was predicted more than 20 years ago. But with a dense haze preventing a closer look it was not possible to confirm their presence; that is until the Cassini flyby on 22 July 2006.

I think the Cassini mission to Saturn and the Huygens probe were also spectacularly successful.

Infrared images by the robotic Cassini spacecraft of the north pole of Saturn have uncovered aurora unlike any other seen previously in our solar system. The strange auroras are shown in blue in the above image, while the underlying clouds are shown in red.

Also, the Mars Exploration Rovers (MER): They did much more than we thought that they were going to be capable of doing on Mars.

NASA's Mars Exploration Rover Opportunity spent its seventh anniversary of its landing on Mars investigating a crater called "Santa Maria," which has a diameter of about the length of a football field.

I think that it is just cool that we are able to go around and explore the Martian surface. We learned some interesting things about the Martian chemistry from MER, but MER was basically a proof of concept -- that we could design automated rovers to go around and explore the Martian surface. Of course Mars Science Laboratory is a bigger version thereof, and I hope that it will do fabulously.

"The Blueberries are my favorite discovery by the MER rovers." --Jim Kasting

Another one of my favorite images from space is the Crab Nebula from the Very Large Telescope (VLT). It is pretty spectacular -- I keep a copy of it in my home office.

The Crab Nebula, filled with mysterious filaments, is the result of a star that was seen to explode in 1054 AD.

Read More:

People:

• Jim Kasting's People Profile

Missions:

• Hubble Space Telescope Mission Page
• Voyager 1 Mission Page
• Voyager 2 Mission Page
• Cassini Mission Page
• Mars Exploration Rovers Mission Page

Planets/Moons:

• Jupiter's Planet Page
• Saturn's Planet Page
• Uranus' Planet Page
• Neptune's Planet Page
• Titan Moon Page
• Mars' Planet Page

Last Updated: 30 October 2012