ROBERT SIEGEL, host:
Scientists are gleefully rummaging through some treasures from outer space. NASA's Messenger spacecraft flashed past Mercury on Monday and took more than 1,200 pictures of the planet - it's still beaming them down to Earth.
NPR's Richard Harris visited the project's lead scientist today.
RICHARD HARRIS: The first thing you notice when you walk into Sean Solomon's office at the Carnegie Institution of Washington is the Millar balloon in the shape of a giant champagne bottle. It celebrates Messenger's first big success at Mercury, the flyby. The next thing you notice is a technicolored globe on the table of some place that's definitely not Earth.
Mr. SEAN SOLOMON (Director, Carnegie Institution of Washington): That's Mars.
HARRIS: Oh, that's Mars. Do you have one of Mercury?
Mr. SOLOMON: Ah, Mercury effects - just look at this.
HARRIS: Solomon picks up a dented brown orb the size of a giant grapefruit. It's a relic from long ago.
Mr. SOLOMON: All the images came from Mariner 10; that's more than 30 years old, and half the globe is a complete blank because Mariner 10 only saw 45 percent of the surface.
HARRIS: That globe is on its way out. Monday, Messenger took breathtaking photos of a big chunk of Mercury including a lot of terrain that's never been seen up close before.
Mr. SOLOMON: In the words of Bob Strom, who is the only member of our science team who was also a participant on Mariner 10, this is a whole new planet.
HARRIS: Scientists haven't even finished downloading all the images yet, but the first glance is providing real food for thought.
Mr. SOLOMON: Let's see.
HARRIS: Solomon pops open a photo on his computer screen. At first glance, Mercury looks like the Moon, but it's actually quite different to a trained eye. He points out a dramatic fault that cuts a dark jag across the surface.
Mr. SOLOMON: This is like a kind of fault that, on the Earth, you might see it at the base of a great mountain range or that - the kind of fault that's sometimes buried underneath basin sediments, like in the Los Angeles area.
HARRIS: Here, it's an important clue about how Mercury formed. One thought is faults, like this, cropped up because Mercury actually shrank as it evolved. Solomon's also puzzled by dark splotches on the surface splashed up by meteor impacts. But at the moment, he says his reaction to the new images is mostly in his heart, not his head.
Mr. SOLOMON: It's a very strongly emotional reaction when even the scientific team sees these images for the first time because it's like being a tourist in a place that no one has gone.
HARRIS: And the exploration has just begun. Solomon is also anxious to see whether there are signs of water ice in the permanently dark craters near the planet's pole; that, however, will have to wait 'til 2011 when Messenger returns to Mercury for a full year of observations.
Richard Harris, NPR News, Washington.