Half a century ago, when the only images of Mars came from artists' imaginations, few would have predicted two camera-equipped rovers -- and hundreds of thousands of real images -- just one generation later.

"The last 50 years have been stunning," said Jim Bell as the 2007 Olin lecturer before a near-capacity Bailey Hall audience, June 8, during Cornell Reunion. And the next 50, he added, could be even better.

Bell, Cornell associate professor of astronomy and developer of the panoramic cameras (pancams) on the Mars rovers Spirit and Opportunity, spoke on "Postcards From the Solar System: The Next 50 Years of Space Exploration." It was a guided tour of Earth and its neighbors, a look back at the discoveries of the last 50 years -- and thoughts on what might be ahead.

Bell began with Oct. 4, 1957: the day the Soviet Union launched Sputnik, the first man-made object into orbit. That launch, Bell said, was a defining moment for a generation. Space exploration was no longer just about science; it was about national pride.

In the half century that followed, scientists from around the world made discoveries that surpassed expectations. "To call our first 50 years of space exploration a golden age is truly an understatement," Bell said. "We've really completed a reconnaissance of our solar system."

Bell continued with a metaphorical planet-hopping trip through the solar system; pausing to recount recent discoveries -- from the oddly icy poles of Mercury to the detection of planets outside our solar system.

The space program has been particularly valuable for what it has revealed about Earth, he said.

"We have obtained a perspective of ourselves that we never had before," Bell said. "And it's important to use observations from above to understand how the planet is changing."

And NASA's Mars Exploration Rover Mission, meanwhile, is still yielding breakthroughs -- more than three years into its 90-day mission.

The mission has had remarkable luck, he said. "We turn a corner, and we find something new that nobody anticipated. It's been a wonderful mission of discovery that way."

As for the future of space exploration, Bell said the possibilities are vast -- as long as younger generations are motivated to pursue them. The next generation might be motivated by the prospect of space tourism or a desire to protect the Earth from climate change or errant asteroids.

"We need to get this generation excited, inspired about space exploration," he said. "Because, ultimately, they're the ones that are going to have to carry it out. They are going to have to be to invested in it to make it happen."

Though making predictions can be risky, Bell said, he predicted that humans will likely be spending weeks on the moon in the next 15-20 years. And by the 100th anniversary of Sputnik's launch, he added, Spirit and Opportunity may have company.

"People are going to visit and explore Mars within the next 25 to 50 years," he said.

Which is why, Bell added, he has already asked his children a simple favor.

"I told my kids, when my wife and I have our 50th wedding anniversary -- don't go crazy," he said. "Just a weekend on the moon. A week on Mars, maybe?"