Embassy of the United States Ottawa, Canada

An instrument the size of a soda can that is gathering data on the surface of Mars was provided to the Curiosity rover and the Mars Science Laboratory by the Canadian Space Agency (CSA).

The Alpha Particle X-ray Spectrometer (APXS), mounted on the end of the rover's robot arm, is used to identify the elements in the rocks and soils on the Martian surface. APXS may detect iron, sulfur, chlorine or any of 24 other elements it is designed to spot. Each one might tell part of the story about the geologic history of the red planet.

Spectrometers identify materials by measuring the interaction of light wave reflection, emission, absorption and diffraction. Many spectrometers have surveyed the Martian surface from orbit and from the surface. APXS, which measures X-rays emitted from surface materials, was included in the science instrument suite on two previous unmanned missions to Mars.

This newest, fastest version of APXS contributes to the primary objective of the Curiosity mission: to look for signs of a once-habitable environment in the landing zone of Gale Crater. APXS, on the end of Curiosity's rover arm, makes measurements when the arm puts it in contact with a soil or rock target. Interesting soil or rock samples the rover finds can be fed into instruments for analysis.

"There can be different proportions of elements there," said Victoria Hipkin, CSA's senior program scientist for planetary explorations, "and different trace elements that we haven't seen or seen rarely" in samples taken during previous missions.

CSA supports a Canadian team led by Ralf Gellert at the University of Guelph who is the principal investigator for APXS. The team includes the University of New Brunswick, NASA's Jet Propulsion Laboratory, Cornell University, the Rensselaer Polytechnic Institute and the Australian National University. The prime contractor for APXS is MacDonald, Dettwiler and Associates, a multinational communications and information company.

Hipkin said about 50 Canadian scientists and engineers have worked on development of APXS since NASA selected the mission in 2004. The team built a compact, sensitive electronic instrument that has to perform in extreme conditions of temperature and barometric pressure. Hipkin said Gellert and the CSA team watching the first several months of the APXS's performance are "extremely happy" with how it is functioning.

APXS is one of 10 scientific instruments aboard the Mars Science Laboratory (MSL). The MSL analysis may allow the ground team to detect, Hipkin said, "the presence of key minerals that formed in water and will only form under certain conditions." Those results, in turn, would allow some deductions about how much water once existed where a soil sample is taken and how long it stayed there.

Tracking down those elements and deciphering the story they tell is "a big part of this mission," Hipkin said. She said APXS is also good at analyzing the different types of salts that are likely to be detected in the soil. "By then trying to interpret these different salt compositions, we get to more of the story about what has happened to water on Mars," Hipkin said.

Curiosity landed on Mars in early August 2012 for what is supposed to be an almost-two-year mission. NASA reports that the craft is carrying the most advanced array of scientific equipment ever used on Mars.

The mission has broad international participation, with other MSL instruments provided by Spain's Ministry of Education and Science and Russia's Federal Space Agency.

Some of the early photos sent back by Curiosity provided evidence of what scientists say was a streambed, a site of flowing water, at some point in the Martian past. The unmanned craft has also sent back vast panoramic photos of a dry landscape that resembles some desert environments on Earth.

Understanding Mars' transition from a warm, wet planet to a dry, cold one may also provide greater insight on how changing environmental conditions could affect our home planet.