So here's what we did: we went around the AAAS exhibit hall and took pictures of any sign that made us think of something sexual or made us want to yell the word "dude!" really loudly. When we took the picture of the PNAS sign, the guy in the booth looked all suspicious and said, "Are you making fun of our sign?" We admitted that we were, but he was really nice about it. Nobody else even noticed that their signs were dirty. Even the chick whose poster said "talking dirty" on it.

OK, fine. So what we did wasn't really that mean and just shows that we are a bunch of immature dorks. But in our defense, we did do a public service. We took a stack of "pocket guides" on WMDs from the FBI's booth and handed them out at the airport. You know, for science education.

* Actually, we didn't really steal the skulls. That guy in the picture did.

• Richard Cook, designer of MSL, said that it's three times heavier than Spirit and Opportunity, the two rovers currently on Mars right now. It's powered by nuclear energy, designed to last 20 years, travel 10 km, and comes equipped with a laser for vaporizing rocks so it can do chemical and mineralogical analysis on them. "We call it the death ray," he confessed. Joked NASA Jet Propulsion Lab Director Charles Elachi, "In a few years people will be visiting Mars and see bullet holes all over the place [from the laser]."
• When Cook and his team were designing Spirit and Opportunity, they wanted to do what he called a "built to print," meaning to the specs on paper. They wanted to base it on the model they'd developed for Sojourner, the previous generation Martian rover. But immediately they figured out that wouldn't work, especially with the more-complicated MER rovers, since they still had to fit inside a small lander. "it's hard to take a rover and put it inside a tetrahedron," Cook said with a laugh, referring to the shape of the lander.
• The MSL rover, which will blast off next year, will be able to do experiments that tell us a lot more about Martian water sources. It can do gas chromatography mass spectrometry (GCMS). It has an onboard camera.
• Steve Squyres said he was disappointed when Spirit landed in Gusev Crater, which he hoped would be a lakebed. Instead, it was covered in a layer of lava rocks. "I believe the lakebed is there, but it's covered in lava," he said. Luckily, Spirit was able to make it to the Columbia Hills nearby to study a wide variety of rocks.
• Some of the rocks that Spirit studied show strong evidence of having been saturated by water, probably steam. Most likely, the hit that created the Gusev Crater shot a bunch of superhot rocks out to the Columbia Hills, and these melted ground water into steam.
• "When we talk about water on Mars, what we really mean is sulfuric acid," Squyres explained with a grin.
• There is absolutely no doubt that there has been water on Mars, Squyres said, but the fact is that the ratio of water to rocks has always been very low. One piece of compelling visual evidence he showed us was from a study of the sorts of patterns water leaves in soil over years of flowing on it. He compared images of a characteristic, smile-shaped pattern created by waters from the Colorado River with images from rocks on Mars. The smile shapes and sizes were nearly exactly the same.
• The rover Opportunity is currently at the Victoria Crater, where it is studying layers in the cliffs to learn more about the geological history of Mars. Some layers make it clear that water did at one point saturate the planet's surface. The walls of the crater are so steep that scientists have to pilot the rover based on satellite images taken by a recently-arrived spacecraft. He showed us images from the spacecraft, which are so high-resolution that you can see Opportunity and the shadow of its antenna at the edge of the crater.
• About the Victoria Crater mission, Squyres said, "It takes a lot of guts to drive an 8 hundred million dollar piece of equipment along the edge of a cliff on another planet."
• Andrew Knoll said that the real question isn't whether there has been water on Mars, because surely there has been. The question is whether that water is habitable for life as we know it.
• Unfortunately for people who want to meet alien life, the prognosis is not good. Chemical and mineral evidence suggests that water on the planet is so salty and acidic that it wouln't support any organisms we know. "Water on Mars would be challenging for life as we know it," he said.
• Knoll added that water could have flowed on Mars if it was extremely salty because salt lowers the freezing point of water. Or it could have flowed as a result of asteroid hits that temporarily melted ice.
• MSL will do more definitive mineral analysis to determine what the chemical composition of Martian water might have been (or might be).
• There has been a lot of debate over the Martian "gullies," structures that look like they were cut into the Martian surface with water. Squyres said, "Some were created during the last five years and look like they've been created by water. But all the ones we've looked at have slopes that suggest they were probably caused by avalanche not water."