美国国家公共电台 NPR Another July 4th Anniversary: Pathfinder's Landing On Mars（在线收听）

ROBERT SIEGEL, HOST:

Twenty years ago tomorrow, a plucky little NASA probe called Pathfinder landed on Mars. Actually, it didn't so much land as bounce down to the surface. Its final descent was cushioned by giant airbags. Pathfinder carried with it a pint-sized, six-wheeled rover called Sojourner. NPR science correspondent Joe Palca was at Mission Control at NASA's Jet Propulsion Laboratory on landing day. He spoke with me then and he's back with me now. You're still here. Hi, Joe.

JOE PALCA, BYLINE: Yeah, I can't get away. No, it was an amazing day.

SIEGEL: Pathfinder wasn't the first NASA spacecraft to land on Mars. It wasn't the last. What was so important about this one?

PALCA: Well, it had been a long dry spell. It had been 21 years since NASA had landed a serious spacecraft or a serious probe on Mars. And there was a lot of excitement. This airbag landing system was, like, pretty wacky. The thing came in at 30 miles an hour and bounced 50 feet in the air. Fifteen times it bouncy, bouncy, bouncy before it came to rest and opened itself up and then spread out its petals, which had solar panels in them.

SIEGEL: After it got to work, what were the most exciting things that we learned about Mars thanks to Pathfinder?

PALCA: Well, it landed in a place where water seemed to have once flowed. And the kinds of rocks it was seeing and some of the chemical composition that it detected seemed to suggest that Mars was once a warmer, wetter place, as opposed to the dry, cold place it is today.

SIEGEL: Back in 1997, you were at the Jet Propulsion Lab in Pasadena, Calif., when Pathfinder touched down on Mars. Remind us what it was like that day.

PALCA: Well, it was so intensely exciting because this mission was a smallish mission. I mean, it was put together in three years. I don't remember the exact number - $265 million, you know, chump change for a space mission. And so I - all the people who worked on it, it was like they had built it in a garage and taken it down to Kennedy Space Center and launched it into space. And it had - so it had that sort of, wow, is this really going to work quality to it. And when it did, you just cannot believe the excitement that the scientists and engineers felt. And there's a clip here from Matt Golombek, Matthew Golombek, who was the lead scientist. And it captures that exactly.

(SOUNDBITE OF ARCHIVED RECORDING)

MATTHEW GOLOMBEK: We have basically the perfect site. We have the perfect spacecraft. We have the perfect instruments. And we have the perfect rover. And now we're just more excited than you could possibly believe to go out there and start to investigate what's there.

SIEGEL: And 20 years after all that, where are we when it comes to Mars exploration?

PALCA: Well, Pathfinder set the path for the two rovers that came next in 2003, Spirit and Opportunity. They used air bags. Curiosity, which landed a few years ago, didn't because it was too big. So the days of airbags seem to be gone. But there's another mission to be launched next year that's going to measure the geophysics of the planet and a couple more in 2020. So NASA and ESA, the European Space Agency, everybody loves Mars.

SIEGEL: Now, there's something that you've been embarrassed about for 20 years.

PALCA: Yes.

SIEGEL: And I ought to be equally embarrassed, but for some reason less so. I read in the introduction to our conversation on that July Fourth a number of how far Pathfinder had traveled that had been supplied by you...

PALCA: That's right.

SIEGEL: ...And edited by the NPR Science Unit and gotten past my editor here.

PALCA: Yep.

SIEGEL: And I applied not full brain power and read it. I said that this - it had gone farther than New York City is from Washington, D.C...

PALCA: That's right. You said...

SIEGEL: ...Three hundred miles.

PALCA: That's right. You said it had traveled for seven months and more than 300 miles.

SIEGEL: Yes.

PALCA: And of course, we left off the million.

SIEGEL: It had gone more than 300 miles, though.

PALCA: We were - strictly speaking we were right. But it does leave a measure of...

(LAUGHTER)

PALCA: ...What shall I say - misleading people. I mean - and I don't - I mean, I'm sure most people know that Mars is further than 300 miles away. But I didn't want people to think that I thought or you thought it was something like 300 miles away. And that's been - I've felt bad about that for 20 years. So I really - I really appreciate you giving me a chance...

(LAUGHTER)

PALCA: ...To rectify that. Oh, you know, who says you get another chance? But you get another chance.

SIEGEL: Joe Palca. Thanks for talking with us.

PALCA: You're welcome.