Each year's meeting of the American Association for the Advancement of Science (AAAS) seems to include at least one session on the search for ET. This year was no exception, with some very interesting presentations on what astrobiologists look for, the plans for the next Mars rover, and the role of NASA's Planetary Protection Officer. You can read about that final one in a later post, but for now, let's take a look at what astrobiologists spend their days doing, and how the new Mars rover, to be named Curiosity, will help them do it.

At the AAAS meeting, Dr. Michael Meyer, lead scientist for the Mars Exploration Program, discussed some of the greatest hits and biggest challenges in astrobiology. At a basic level, astrobiologists look for signs of life on other planets, in part as a way of better understanding life on Earth. We know that life on our planet is extremely resourceful; the same year that the Viking missions went to Mars, we discovered life miles underwater around geothermal vents. Microorganisms have also been found living more than a mile and half underground, sustained not by sunlight but by the heat of radioactive decay, and we know from experiments on the International Space Station that lichen can survive the vacuum of space.

But recognizing life can be harder than you might think. There is still disagreement over whether or not the meteorite ALH84001 shows signs of bacterial life on Mars. There's a bit of a kerfuffle going on right now over whether or not NASA astrobiologist Richard Hoover has found fossilized bacteria in another meteorite. The problem is that if you make a Venn diagram representing features created by life and features created by nonbiological processes, there's a significant overlap.

Many of these and other key questions in Solar System science can be addressed by Mars; Solar System history, planetary evolution, and the potential for life. The planet has a well-preserved record of its climate and geologic evolution, much better in fact than on Earth, where plate tectonics, glaciations, and weather have eroded much of its history. It's also the most accessible place in the Solar System to study these questions.

Andrew Steele, of the Carnegie Institution for Science, took to the podium to go into some detail about the Mars Science Laboratory and Mars Sample Return missions, the next two steps in our exploration of the Red Planet. As with Dr. Meyer, Dr. Steele emphasized that the primary motivation for searching for life on Mars is to help us understand more about life on Earth: What can Mars tell us about early life on Earth? What do Martian and terrestrial organic chemistry have in common with each other? If there isn't any life on Mars, why is that? And if there is (or was), what is (or was) it like?

The current Mars rovers, Spirit and Opportunity, have been amazing successes. Operating well beyond their planned 90-day lifespans, Opportunity continues to be a mobile science platform, 2532 Earth days after landing on the surface of Mars. The next rover, Curiosity, will be much larger and much more advanced, about the size of a Mini. Working as a robotic field geologist, it is designed to have a long life, with the ability to traverse miles over rocky terrain, and then survey the composition of bedrock and regolith. It will also have mobile geochemical and environmental labs on board, and will acquire and process multiple samples.

Curiosity has four potential landing sites: Mawrth Vallis, Gale Crater, Eberswale Crater, and Holden Crater. Each has been chosen because they show signs of ancient flowing water. As Curiosity travels around, it's going to measure the spectrum of surface radiation on Mars; look at the role of water, geology, and geochemistry; and look for biological potential. However, it won't attempt to detect life in the way that the Viking landers did.

Actually engineering a semiautonomous robot to do all of this is quite complicated, as you might imagine. There's a 7-minute radio lag from Earth to Mars, so remotely driving it around won't work. To see where it's going, Curiosity will be equipped with stereoscopic cameras and programming that let it conduct 3D models of the terrain and find the best possible route to its point of interest. It has a "chemcam," a device that pulses lasers at rocks of interest, vaporizing bits of them to let it study the rock chemistry without even touching the sample.

But Curiosity will also have a core-sampling drill that will be able to store samples for return to Earth on a future mission, Mars Sample Return. Bringing samples back to Earth is important because there's a real limit to the kinds of assays you can conduct with the size, power, and durability constraints that need to be taken into account with a rover.

Dr. Steele discussed the actual decision loop that Curiosity's team will go through every day, and it's rather interesting. It starts with looking at the previous day's uploaded data. The team then decides where they are in the science plan and have an engineering meeting to give feedback to the controllers ("move lens A to angle X," and so on). Instructions are then sent to the rover to execute different bits of pre-written code. The rover wakes up, performs its system checks, then follows the day's instructions, finally uplinking its data to a satellite in Mars orbit, which relays that back to the team on Earth, enabling the process to start all over again. Since computation is pretty energy intensive, that's all done on Earth.

Curiosity is in testing on Earth right now, and you can follow it on its adventures via Twitter, just like its predecessors. I don't know about you, but I can't wait to see the results start coming in. Curiosity is set to launch in November this year, and should land in 2012.

Listing image by NASA