A view of Mars taken by the Mars Exploration Rover Spirit
TIME.com: Have any of the initial discoveries been surprising?
Kluger: The biggest surprise so far is the dark patch of dirt that was dragged by Spirit's airbags during landing. It resembles mud, but it can't be mud, because of the absence of water, and therein lies the mystery. Mars may have at one time held water, and one place it might be found is the Gusev Crater, an area about the size of Connecticut that was Spirit's landing spot. The crater may have once been a lake, and scientists feel that spot gives us the best chance to try to determine if any part of Mars was ever hospitable to life.
TIME.com: Will Mars mean anything more to us in our lifetimes?
Kluger: Anytime you go somewhere it means more to you. The more contact you have with something, the more you learn about it. Does it mean that it might in time be common for people to go to Mars? With an unlimited amount of money and resources and time, there are scenarios which could make that a possibility.
The biggest hurdle right now in terms of sending humans to Mars is the exposure to radiation. But all of this is simply scaling up on existing technology. It took only nine years to send a man to the moon after starting from scratch, so we're in a better position here.
TIME.com: How much did the Spirit mission cost, and has it been worth it?
Kluger: The cost is $850 million, and we won't know whether it was worth it until the science is returned. But we do know that it's possible to get a spacecraft bigger and more sophisticated than Pathfinder there. And don't forget the old axiom that says there's no such thing as a failed experiment, because failures teach you what doesn't work.
TIME.com: Will space exploration ever captivate the public again like it did in the 1960s?
Kluger: The landing of Pathfinder on Mars in the summer of 1997 was the closest I've seen to people really gathering around TVs and being as excited as they were in the 1960s. There is potential for that feeling to return this summer, when the Cassini-Huygens spacecraft arrives at Titan, a moon circling Saturn.
Having a human onboard of course makes for a much more captivating mission. That's why I feel that even a trip to the moon, which we became nonchalant about as early as 1972, would bring back a sense of wonderment about space exploration. A large segment of the population has not seen a human walk on the moon. And getting a person anywhere close to Mars would be thrilling.
TIME.com: What's next on NASA's to-do list?
Kluger: First, a continuation of the Mars program. The idea is to have a spacecraft ready to explore every two years, when Earth and Mars grow closer.
An unmanned mission to Pluto, which would take about nine to 11 years for arrival, is back on the drawing board. It probably should've happened already, and it remains a possibility.
Also, further study on Jupiter's moon, Europa, which is about the size of the Earth's moon, and is believed to possibly contain water beneath its icy crust.
For now, manned space programs are in kind of a black hole. The space shuttle program and the International Space Station were both troubled and costly.
Next week in TIME and on TIME.com, more photos, graphics and what's next for Spirit's exploration of Mars.
More Mars-Related Links:
Mars Exploration Rover Mission — NASA official, user-friendly mission site, with photos, explainers and sections for kids and students.
Mars: Dead or Alive — A resourceful companion site the TV special that aired on PBS on Jan. 6.
Look Up There — William Safire writes in the New York Times that "the cooperative competition in space is inspiring" as "the desire to be first is there, but the fear of being beaten is less."
Most Detailed Image of Mars Shows Mysterious Substance — A Washington Post report on the mud-like substance that has proven to be a mystery on a surface that was expected to have been bone-dry.