The experiments, which will fill a $32-million payload aboard the spacecraft, will attempt to study radiation dangers on Mars, search for signs of life, examine dust devils and possible electrical storms and demonstrate that breathable air and rocket fuel can be produced from the planet's carbon dioxide atmosphere.

The forward-looking project is being developed under NASA's Human Exploration and Development of Space (HEDS) unit as the lander's secondary payload. The spacecraft's primary mission is to drill rock cores from the surface, load them into a small rocket and blast them into Mars orbit for an eventual return to Earth.

As little as scientists know about Mars, they know even less about the dangers astronauts might face when traveling there. The prospect of sending humans to Mars raises volumes of questions that need to be answered before any such mission can be realistically considered. For instance:

What is the cancer risk to astronauts on Mars? Could high radiation levels cause chromosomal damage that could affect an astronauts' ability to have healthy children? Is that planet home to dangerous bugs -- bacterial or viral life forms -- that could infect visiting astronauts? Will astronauts need hurricane shelters to protect them from dust storms that rip across the planet? Do electrical storms and lightning-type discharges threaten spacecraft computer systems?

And if astronauts do get to Mars, what will they breathe? Can breathable air be produced on Mars? What about rocket fuel?

NASA announced the provisional selection of the four HEDS packages last week, but requested significant changes in two of them. This week scientists, engineers and project managers are meeting at the Jet Propulsion Laboratory in Pasadena, California to work out the details of fitting it all together.

"We'll be hashing out a lot of the technical details and also the funding issues," said Peter Ahlf, who leads HEDS projects in NASA's Life in Microgravity Science and Applications Office. "That will be followed up with some work over the holidays and we'll try to bring it to closure by mid-January." Ahlf set January 13 as the target date for when the exact anatomy of the package should be finalized.

The four proposals that have been tentatively approved are:

• A radiation experiment called the Martian Neutron Energy Spectrometer, or MANES. The device is designed to test for potential radiation dangers caused by the interaction of cosmic rays with the martian atmosphere and with spacecraft structures. Click for more.
• The Mars Organic Detector, or MOD. This experiment will test surface samples for organic molecules that may hold clues about whether life ever existed on the Red Planet. Click for more.
• A portion of an atmospheric dust experiment called the Mars Investigation of Total Climatological Hazards, or MITCH. The selected part incorporates a sort of laser radar with an imaging camera to scan the landscape for dust devils and take pictures of them. In addition, NASA wants to include a set of instruments that will test the electrical charge of dust storms and the martian atmosphere. Click for more.
• A miniature production plant to make oxygen, nitrogen and methane from the planet's mostly carbon dioxide atmosphere. These gasses can be used to produce breathable air and rocket fuel. The package is being called PROMISE, which stands for Production of Resources on Mars In Situ (on site) for Exploration. Click for more.