RAY SUAREZ: As part of its mission to understand the history and properties of the Martian arctic, the Phoenix Lander took several pictures earlier this week of a trench near the spacecraft. Those photos, as highlighted here, showed eight small chunks of white material.
Four days later, the Lander took photos of the same spot again, but this time the material was gone. And as the researchers say, there’s only one explanation: ice that evaporated.
To help us understand these findings, we turn to the lead scientist for the mission, Peter Smith of the University of Arizona.
And when did you get the first signs that you may have located ice so close to the Martian surface?
PETER SMITH, University of Arizona: The first chance we had to see the surface itself was looking underneath the Lander with our robotic arm and its camera.
And we saw that the thrusters had pushed away the local soil, the dry soil that we see around us, and exposed an underlying layer, which was both bright and hard. Some of us thought that was ice, but we couldn’t prove it from just that picture.
RAY SUAREZ: How do you know it’s frozen water, as opposed to another substance, like frozen carbon dioxide, what people call dry ice?
PETER SMITH: Frozen carbon dioxide is certainly a logical choice here, because in the winter it’s probably 30 centimeters deep in frozen carbon dioxide. But as the temperatures warm up in the arctic summer, it gets way too warm for carbon dioxide ice. It would be like finding snow in the desert in the summer. So it’s very unlikely, if not impossible.
The discovery's significance
RAY SUAREZ: Now, I was thinking back to when I was kid, and I thought scientists always knew there was ice on Mars. Why is this being treated as such an important milestone?
PETER SMITH: Well, this is certainly not the final goal of our mission. We've known there's an exposed ice cap in the northern pole of Mars for over a hundred years.
And only six years ago, the odyssey orbiters made some discoveries that scientists interpreted as being an abundance of hydrogen inside of the arctic circle on Mars. And hydrogen is not usually found by itself, so they assumed it was water ice near the surface.
But they didn't have high resolution; their resolution's about the size of the state of Arizona. So our mission was inspired by that discovery, and we have landed in a place where we think there's going to be lots of ice, but it's only today that we are sure that we are going to be able to interact with this ice and learn its history.
RAY SUAREZ: So you uncovered what looked like ice. Then it, what, melted or evaporated? What happened to it after you exposed it?
PETER SMITH: Well, in the temperature regime we're at on Mars, it's quite cold there. It's between minus 22 Fahrenheit and minus 120 Fahrenheit, depending on whether it's noon or midnight.
And we were expecting that the ice would not go through a liquid phase, but would either just evaporate directly into vapor or to somehow change its properties, and so that's exactly what we saw, is these little chunks of the white material evaporated into vapor and disappeared.
And that's a very common property for ice at this temperature. And, in fact, we can't think of anything else that would do that.
RAY SUAREZ: So you've got tools aboard the Lander that will help you collect some ice samples and take a better look at them?
PETER SMITH: Exactly. What we want to do is get these ice samples and the soil above it into our instruments to analyze the minerals, the chemistry, and the microscopic shapes and sizes of these little grains that we see.
And it's through this analysis that we learn whether the ice has melted, that we understand the history of the ice. And water by itself in a frozen form doesn't interact with the soil, but as a liquid it changes it rapidly. It will add salts, and it will change the minerals into carbonates, and sulfates, and perhaps clays.
And by looking for those sort of secondary materials that are formed by the action of liquid water, we can understand whether this was a place where it was once wet.
Temperatures shorten the mission
RAY SUAREZ: Well, you mentioned it's very cold. You'll be able to melt it yourself using tools on the Lander?
PETER SMITH: Yes, we have little ovens. We can heat those samples up to 1,800 degrees Fahrenheit. And as we heat them up, we drive off the different vapors for the different minerals that are inside of these soils. And we'll be able to tell very exactly just what the composition is.
And in addition, we can tell if there's any organic material associated with this ice, because liquid water and organic materials are the basis of what we call a habitable zone. And it's this habitable zone that we're looking for on Mars.
RAY SUAREZ: Do you have a limited time window? When does Martian winter come and make it tougher for you to do your work?
PETER SMITH: Well, you're absolutely right. We're there at the height of summer. In fact, next week is the Martian solar solstice, the summer solstice, and that's the hottest time of year in this area.
And as we progress through our mission, by the time we get to next February, we'll be frozen into this two-foot-deep layer of carbon dioxide ice and we'll have no solar power. So that's the end of our mission.
RAY SUAREZ: Peter Smith, thanks for explaining what you've found so far. Good to talk to you.
PETER SMITH: Good to talk to you, Ray. Thank you very much.