Mars within Los Alamos' Neutron Spectrometer's Reach
20 Oct 2001
(Source: Los Alamos National Laboratory)
Los Alamos National Laboratory
LOS ALAMOS, N.M., - A neutron spectrometer designed and built at the U.S. Department of Energy's Los Alamos National Laboratory is closing in on Mars aboard NASA's 2001 Mars Odyssey.
A similar Los Alamos instrument aboard NASA's Lunar Prospector provided compelling evidence for water-ice at the moon's poles.
The 2001 Mars Odyssey mission is designed to map the mineral and chemical make-up of the Martian surface and the location of water and shallow buried ice, and for the first time study the radiation environment of the planet to gauge the risk for future astronauts.
Los Alamos' neutron spectrometer will map the water table in the upper meter of the Martian soil, helping scientists to understand the climatic history of the planet and also providing information on the location and quantity of water available for future exploration and possible colonization. The neutron spectrometer will also map the basaltic lava cover, measure the seasonal variation of dry ice snowfall at the poles and help convert gamma ray data from another instrument that will determine the quantity and composition of various elements on the planet.
"I am nervous as heck," said Bill Feldman, Los Alamos' principal investigator on the design and construction of the neutron spectrometer. "We've been here before in 1993 with the Mars Observer, and that spacecraft was lost. But everything is going great with the Odyssey's approach so far. NASA did the last trajectory prediction calculation on Oct. 18 and Mars Odyssey is right on target, right on the money. It is within one kilometer of where they want it to be."
Mars Odyssey, after a six and one-half month, 286 million-mile journey, is scheduled to enter into orbit around the red planet at 8:30 p.m. Mountain Time on Tuesday. Once in orbit, the spacecraft will gradually tighten its elliptical path to get into an orbit appropriate for science mapping. By late January or early February all instruments aboard Mars Odyssey, including the neutron spectrometer, will begin sending data about Mars back to Earth for a planned 917 days.
The neutron spectrometer also collected background and calibration data while cruising to Mars. The neutrons were created when galactic cosmic rays bombarded the spacecraft. "We've already analyzed data from the cruise and it is really beautiful. Our instrument is working great," said Feldman. "The cruise data will be extremely useful for calculating the amount of radiation exposure astronauts might receive traveling to and from Mars." Feldman and his colleagues are preparing a paper for the scientific publication Geophysical Research that analyzes these data.
For planetary measurements, neutrons are generated when galactic cosmic rays slam into the nuclei of atoms on the planet's surface, ejecting neutrons skyward with enough energy to reach an orbiting spacecraft. Elements create their own unique distribution of neutron energy - fast, thermal or epithermal - and these neutron flux signatures allow scientists to determine the general distribution of the soil's elemental composition based on the data received from the instruments.
By looking for a decrease in epithermal neutron flux the scientists can locate hydrogen. Hydrogen in the soil efficiently absorbs the energy from neutrons, preventing them from escaping the surface and being detected by the spectrometer. Since hydrogen is most likely in the form of water-ice, the spectrometer will be able to measure directly, a meter deep into the Martian surface, the amount of ground ice and how it changes with the seasons.
Los Alamos' neutron spectrometer will map Mars' basaltic lava by measuring fast neutrons indicative of iron, a major component of the lava. Studying Mars will help answer questions about Earth's formation and the origin and evolution of the solar system.
Other instruments aboard NASA's 1,600-pound spacecraft include a thermal-emission imaging system, a gamma-ray spectrometer, a high-energy neutron detector and a radiation monitor.
Los Alamos has been flying neutron spectrometers in space since 1963 in support of the U.S. nuclear treaty verification program. The present design used for Mars Odyssey was developed in mid-1980 in support of the U.S. strategic defense initiative.