Early in his career, Professor Craig Kochel, geology, examined evidence that water existed on Mars billions of years ago, and he conducted research suggesting that groundwater, not dry sand movement, could have caused the land formations captured in images by NASA. He discusses that work, along with the significance of the NASA's recent announcement that water currently exists on Mars, the technology that made it possible and the next steps the scientific community might take.
Q: What's the significance of the NASA's recent announcement that water exists on Mars?
A: We have known for decades that water existed on Mars billions of years ago, and we've known that water in the form of ice exists there, but this new announcement suggests that there are a large number of places around the planet where water is seasonally active. It's a hugely significant discovery for geologists because it suggests that water is still an active surface landform modifier on Mars. But in terms of the ultimate reason NASA is interested in water on Mars — it's the potential for life there. You can't have life as we know it without water. The discovery is also a big deal because now we know there's a potential source of water if we put humans on Mars. It's poisonous, you can't drink it, but you could modify it and get regular water out of it, and it could be used for rocket fuel. To me, it's a big deal because we've been fooling with this question of water on Mars for a long time and seeing lots of circumstantial evidence.
Q: The search for water on Mars stretches back to the 1970s and '80s. Can you tell us a bit about the history of the search and your involvement in it?
A: This recent discovery brought me back to my graduate school days in Texas in 1977, when I worked with Victor Baker, a prominent researcher on Earth rivers but on Mars water as well. He came into my office with orbital photos of Mars from NASA's Viking program. He brought in a wheelbarrow of boxes of those images and said he was going to Australia for a month and wanted me to put the images together, figure out where they were on Mars, and map and interpret them.
One set of photos shows part of a large channel called Kasei Valles, which is about 5,000 miles long. It has all these streamlined features in it indicative of catastrophic floods at one point. From that we made the first geomorphic maps of Mars channels and suggested an analog to the biggest floods known on Earth, the Missoula floods that took place in the Pleistocene era in what is present-day Washington State (an area known as the Channeled Scablands). We did a detailed analysis of the shapes and the forms, which pointed to water erosion. Based on the density of craters in the channel areas, we knew that water had been on Mars more than a billion years ago, but no one knew where the water came from or where it went.
In the 1980's, researchers mapped small channels all around the planet that weren't related to floods but maybe to rainfall. There came this idea that a lowland in northern Mars might have been once an ocean that these channels emptied into some kind of a salty ocean, and that Mars actually previously had sort of a water cycle. Several rovers, including Curiosity, also found evidence of past water — mineral salts, cross-bedded sand and other sedimentary features suggesting they were formed by flowing water. Recently, rovers have found evidence of large lakes in some of the Martian craters. All along researchers kept seeing features on hillslopes known as gullies (particularly common along the insides of steep crater walls). Gullies eroded recently into hillslopes are widespread on Mars. Related features news with the recent discovery, the recurring slope linae, coming down the sides of craters. There was a big argument: Were these dry sand falls, or were they caused by modern water coming to the surface? Even with detailed pictures from the HiRise camera on the Mars Reconnaissance Observer, the scientific community couldn't agree.
When I was a faculty member at Southern Illinois University, I was awarded a couple of NASA grants to look at whether those channels could form through water seeping out of the ground. The idea was that whatever water might have been on Mars early on might have gone into the subsurface and existed there as permafrost — and that was backed up by looking at impacts of asteroids making craters. Instead of the spray pattern of ejecta we get on the dry moon from crushed up rock, we see a flow pattern coming out of the crater. We suggested, along with a lot of other people, that there still could be groundwater present that's liquid, and that it could come out on the surface and maybe flow for a little bit before it evaporates and freezes in the cold Mars atmosphere, which is almost a vacuum. So we conducted experiments in a flume similar to the one we have Bucknell (and we've done some of those experiments at Bucknell since) where we allowed water to seep through wedges of sand. Springs start to emerge on the slope and form canyons without rainfall, showing that those sorts of configurations can be caused by groundwater seepage (called sapping). Interestingly, the sapping canyons formed had a morphology distinct from channeled formed from surface runoff but very similar to that in the Martian channels.
Then we went to places around Earth where we could see this process happening, including some of the driest places on Earth in the Colorado plateau of Arizona and Utah. We put together a field guide for NASA and took representatives on a field trip to show them features that are formed by groundwater sapping. We found similar formations in Hawaii, too. So, way back in the 1980s, we were suggesting that maybe even in the present environment, groundwater could be seeping out. But we didn't have the resolution of photographs prove anything conclusively.
Q: What changed to allow scientists to confirm the existence of water now?
A: Better technology. With the images from the HiRise camera, researchers were seeing these dark areas (streaks) on the slopes come and go with the seasons, and those slopes didn't have an ice source above them, so they thought the water was coming from a permeable zone in the rocks allowing water to flow out. The water hits the cliff and flows for a short period of time until it evaporates. In the wintertime, these marks disappear and in the summer, when it's warmer and the ice can thaw, they reappear again. But that still wasn't enough proof.
What sealed it up was, in addition to the pictures from the HiRise camera, was another instrument on board the Observer: the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). CRISM did spectral analysis to confirm what the material was made of. When CRISM shot in the winter, it didn't see any evidence of water, and when it shot in the summer overtop of those dark areas, it proved it was water. It's not pure water — it's a salty perchlorate — but it's something that would have a much lower melting point than water and could exist for a while in the Mars environment. You can look at photographs, but you still can't know quite what the material is made of until you get that chemical analysis.
Q: What do you think researchers will do next?
A: It's hard to say, but I think the researchers will try to find more places where they can get the spectral analysis to use as backup proof of what they're seeing visually in the photographs. Then they will have a really strong argument that these aren't anomalous areas. They're probably already looking for patterns of latitude and longitude or topography that show whether these lineae are more common in one location than others. They may also see if their location relates to some of the thermally active areas on the crust of Mars, perhaps where there may be remnant geothermal activity related to ancient volcanism keeping certain areas warmer than others. They could also look for patterns to suggest there areas of active near-surface water, while other areas might just simply be too cold or too deep. The study that came out was a really nice example of how scientists can make observations for years, but they can't come out and make a definitive statement until a they have gone through a long-term, careful period of observation paired with chemical signatures or other evidence.